Chapter XXXI: Appendix: B

RADIO-ACTIVE MINERALS.

Those natural mineral substances which possess marked radio-active properties have been found to contain either uranium or thorium, one of these elements being always present in sufficient proportion readily to permit its chemical separation and identification by the ordinary analytical methods[455].

A large number of uranium and thorium minerals are known at the present time, but they are for the most part found very sparingly, and some of them have been observed to occur only in a single locality. The chief commercial sources of uranium are uraninite, gummite, and carnotite, while thorium is obtained almost exclusively from monazite.

Rutherford and Soddy (_Phil. Mag._ 65, 561 (1903)), were the first to call attention to the important fact that the relations between the various radio-active substances and the other elements could best be determined from the study of the natural minerals in which these bodies occur, since these minerals represent mixtures of extreme antiquity, which have remained more or less undisturbed for almost countless ages. In dealing with these matters, however, it is highly important that we bring to our aid the data furnished by geology and mineralogy, from which it is often possible to determine the relative ages of the different substances with at least a rough degree of approximation. Thus, for example, if a certain mineral occurs as a primary constituent of a rock of remote geological period, it can safely be assumed that its age is greater than that of a similar or different mineral occurring in a later formation. It is, moreover, quite evident that those minerals which are obviously produced by the decomposition and alteration of the primary minerals, through the action of percolating water and other agencies acting from the surface downward, are of less antiquity than the primary minerals from which they originated. Through the application of these considerations it should, in general, be possible to arrange the various minerals roughly in the order of their probable ages.

The most familiar and widely known uranium mineral is uraninite, commonly called pitchblende, which consists essentially of uranium dioxide (UO₂), uranium trioxide (UO₃), and lead oxide (PbO), present in varying proportions. The uraninites can be distinguished as primary, namely, those which occur as a primary constituent of pegmatitic dikes and coarse granites, and secondary, when they occur in metalliferous veins associated with the sulphides of silver, lead, copper, nickel, iron, and zinc. The former varieties are quite frequently crystalline in character, contain a larger proportion of the rare earths and helium, and have a higher specific gravity than the latter, which are always massive and botryoidal.

The following are the most prominent localities in which primary uraninites occur:

1. North Carolina, U.S.A. (especially in Mitchell and Yancey counties). The uraninite is found in a coarse pegmatitic dike which is mined for the mica constituent. The associated feldspar of the dike is considerably decomposed through the action of meteoric waters and gases, and the uraninite itself is largely altered into the secondary minerals gummite and uranophane through the same agencies. Among the associated primary minerals are allanite, zircon, columbite, samarskite, fergusonite and monazite, while the secondary minerals include gummite, thorogummite, uranophane, autunite, phosphuranylite, hatchettolite, and cyrtolite. The geological period of this formation is difficult to establish with certainty, but is stated to be perhaps Archean, or possibly to correspond with the close of the Ordovician or with the Permian.

2. Connecticut, U.S.A. The best known localities are Glastonbury, where the uraninite is found in the feldspar quarries, and Branchville, where it occurs in an albitic granite. Both of these localities have furnished fine crystals. The geological period probably corresponds with the close of the Ordovician or Carboniferous eras, and is stated to be certainly Post-Cambrian and Pre-Triassic. Among the associated minerals are (primary) columbite, (secondary) torbernite and autunite.

3. Southern Norway, particularly in the neighbourhood of Moss. Here uraninite occurs in the augite-syenite and pegmatite. The varieties found are known as cleveite and bröggerite, and among the primary associated minerals are orthite, fergusonite, monazite, and thorite. The period is stated to be Post-Devonian.

4. Llano County, Texas. The variety of uraninite known as nivenite is found here in a quartzose pegmatite, associated with the primary minerals gadolinite, allanite and fergusonite, and the secondary minerals cyrtolite, yttrialite, gummite, and thorogummite.

Secondary uraninite is found at Johanngeorgenstadt, Marienberg and Schneeberg in Saxony, at Joachimsthal and Pribam in Bohemia, at Cornwall in England, and at Black Hawk, Colorado, and in the Black Hills, South Dakota, in the United States. The exact geological period of most of these secondary occurrences is somewhat uncertain, but they are undoubtedly very much later than the primary occurrences mentioned above.

As a matter of general interest the analysis of a typical primary uraninite (No. 1) and of a typical secondary uraninite (No. 2) is given below[456]:

No. 1 No. 2
Glastonbury, Johanngeorgenstadt,
Conn. Saxony

Sp. Gr. 9·59 6·89

UO₃ 26·48 60·05

UO₂ 57·43 22·33

ThO₂ 9·79 ...

CeO₂ 0·25 ...

La₂O 0·13 ...

Y₂O₃ 0·20 ...

PbO 3·26 6·39

CaO 0·08 1·00

He und. und.

H₂O 0·61 3·17

Fe₂O₃ 0·40 0·21

SiO₂ 0·25 0·50

Al₂O₃ ... 0·20

Bi₂O₃ ... 0·75

CuO ... 0·17

MnO ... 0·09

MgO ... 0·17

Na₂O ... 0·31

P₂O₅ ... 0·06

SO₃ ... 0·19

As₂O₃ ... 2·34

Insoluble 0·70 ...

The following list comprises the more important radio-active minerals, with their approximate chemical composition and some notes on their occurrence and probable origin.

Name Composition Remarks

Uraninite, Oxides of Occurs primary
Cleveite, uranium and as a
Bröggerite, lead. Usually constituent of
Nivenite, contains rocks and
Pitchblende thorium, secondary in
other rare veins with
earths and metalliferous
helium. sulphides
Uranium
50-80%.
Thorium 0-10%

Gummite (Pb, Ca) An alteration
U₃SiO₁₂ product of
. 6H₂O? uraninite.
Uranium Formed by the
50-65% action of
percolating
waters

Uranophane, CaO . 2UO₃ An alteration
Uranotil . 2SiO₂ . product of
6H₂O uraninite
Uranium through
44-56% gummite

Carnotite A vanadate of Occurs as a
uranium and secondary
potassium. mineral
Uranium impregnating a
42-51% porous,
sedimentary
sandstone.
Found in
Colorado and
Utah

Uranosphaerite Bi₂O₃ . Alteration
2UO₃ . product of
3H₂O. other uranium
Uranium 41% minerals

Torbernite, CuO . 2UO₃ „ „
Cuprouranite . P₂O₅
. 8H₂O.
Uranium
44-51%

Autunite, CaO . 2UO₃ „ „
Calciouranite . P₂O₅
. 8H₂O.
Uranium
45-51%

Uranocircite BaO . 2UO₃ „ „
. P₂O₅
. 8H₂O.
Uranium 46%

Phosphuranylite 3UO₃ . „ „
P₂O₅ .
6H₂O.
Uranium
58-64%

Zunerite CuO . 2UO₃ „ „
. As₂O₅
. 8H₂O.
Uranium 46%

Uranospinite CaO . 2UO₃ „ „
. As₂O₅
. 8H₂O.
Uranium 49%

Walpurgite 5Bi₂O₃ „ „
. 3UO₃ .
As₂O₅ .
12H₂O.
Uranium 16%

Thorogummite UO₃ . A variety of
3ThO₂ . gummite
3SiO₂ .
6H₂O?
Uranium 41%

Thorite, ThSiO₄. A primary
Orangite, Uranium constituent of
Uranothorite 1-10%. pegmatite
Thorium oxide dikes
48-71%

Thorianite Oxide of Occurs as a
thorium, primary
uranium, the constituent of
rare earths a pegmatite
and lead. dike in
Contains a Ceylon.
relatively Geological age
large probably
proportion of Archean
helium.
Uranium
9-10%.
Thorium oxide
73-77%

Samarskite Niobate and Primary
tantalate of constituent of
rare earths. pegmatite
Uranium 8-10% dikes

Fergusonite Metaniobate „ „
and tantalate
of rare
earths.
Uranium 1-6%

Euxenite Niobate and „ „
titanate of
rare earths.
Uranium 3-10%

Monazite Phosphate of „ „
the rare
earths,
chiefly
cerium.
Uranium
0·3-0·4%

Footnote 455:

An apparent exception has been observed by Danne in the case of
certain lead minerals which occur under peculiar conditions at
d’Issy-l’Évêque, France. See p. 465.

Footnote 456:

Hillebrand, _Am. J. Sci._ 40, 384 (1890); _ibid._ 42, 390 (1891).

INDEX.

_The numbers refer to the pages._

α rays
discovery of, 141
nature of, 141
magnetic deviation of, 142 _et seq._
electrostatic deviation of, 146
velocity of, 148
value of _e_/_m_ for, 148
charge carried by, 151 _et seq._
number of α particles expelled from one gram of radium, 155
mass and energy of, 156
origin of, in atomic disintegration, 157
scintillations produced by, 158 _et seq._
absorption of, by matter, 161 _et seq._
increase of absorption with thickness of matter traversed, 163
relative absorption of α rays from radio-elements, 164
absorption of, by gases, 165 _et seq._
connection between absorption and density, 169
relation between ionization and absorption, 170
theory of absorption of, 170 _et seq._
range of ionization of, 172 _et seq._
complexity of α rays from radium, 174 _et seq._
effect of thickness of layer of radiating matter on emission of, 195
relative ionization produced by α and β rays, 196 _et seq._
phosphorescence by α rays, 202 _et seq._
connection of, with radio-active changes, 235, 444 _et seq._, 455
from the emanations, 263
emission of energy from radio-elements in form of α rays, 419 _et
seq._
connection of heat emission of radium with α rays, 421 _et seq._
number of ions produced by an α particle, 433
absence of, in rayless changes, 454
emission from active products, 454 _et seq._
loss of weight due to expulsion of, 473
α particles consist of helium, 479 _et seq._
magnetic deflection of, from radium C, 543
velocity and _e_/_m_ for, from radium C, 543 _et seq._
diminution of velocity of, in passing through matter, 545
diminution in velocity of, in passing through aluminium, 545
velocity of, when ionization ceases, 545 _et seq._
connection of phosphorescent, photographic, and ionization effects
produced by, 546 _et seq._
energy required to produce an ion by α rays, 551

Abraham
apparent mass of moving charged body, 71, 127

Absorption
law of, in gases, 64 _et seq._
relative absorption of α, β and γ rays by matter, 111
connection between absorption and ionization, 134 _et seq._, 170 _et
seq._
of β rays by solids, 134 _et seq._
connection between absorption and density for β rays, 137
of β rays in radio-active matter, 140
of α rays by solids, 161 _et seq._
of α rays in gases, 167, 170 _et seq._
connection between absorption and density for α rays, 169
theory of, 170 _et seq._
of γ rays by solids, 179 _et seq._
connection between absorption and density for γ rays, 181
of rays from the emanations, 263
of penetrating rays from the earth, 520, 540

Actinium
methods of separation of, 20 _et seq._
properties of, 21
similarity to “emanating substance” of Giesel, 21
possible connection with radio-activity of thorium, 28
emanation from, 249
excited activity produced by, 311
effect of magnetic field on excited activity from, 324
separation of actinium X, 365
decay of actinium X, 365
source of actinium emanation, 365
analysis of active deposit of, 366
radiations from products of, 368
penetrating power of β and γ rays from, 368
products of, 369
table of products of, 449
possible origin of, 464

Actinium A
separation and period of, 367 _et seq._

Actinium B
period of, 368
properties of, 368

Actinium X
separation and decay of, 364 _et seq._
production of emanation by, 365

Adams
decay of activity of emanation from well water, 511
decay of excited activity from the emanation, 511

Age
of radium, 457
of sun and earth, 492 _et seq._

Allan, S. J.
increase with time of excited activity from atmosphere, 505
radio-activity of snow, 506
effect of conditions on decay of activity from air, 519, 523

Allan and Rutherford
decay of excited activity from the atmosphere, 503
ionization of air in closed vessels, 534

Allen, H. S. and Lord Blythswood
radium emanation in Bath springs, 513

Anderson and Hardy
action of radium rays on the eye, 217

Armstrong and Lowry
radio-activity and phosphorescence, 444

Arnold
rays from phosphorescent substances, 4

Aschkinass and Caspari
action of radium rays on microbes, 216

Atmosphere
excited activity from, 501 _et seq._
radio-activity of, due to emanations, 504
diffusion of emanations into, from the earth, 507
effect of temperature, pressure, &c. on radio-activity of, 517 _et
seq._
presence of very penetrating radiation in, 520
comparison of radio-activity of, with radio-elements, 521 _et seq._
amount of radium emanation in, 524 _et seq._
ionization of, due to radium emanation, 526

Atom
number of per c.c., 54
disintegration of, 234 _et seq._
complex nature of, 235
changing atoms, 444 _et seq._
possible causes of disintegration of, 486
evolution of, 496

Atomic weight
of radium by chemical methods, 17
from spectroscopic evidence, 18
emanations, 273
of radio-elements and connection with radio-activity, 445

β rays
discovery of, 113
magnetic deflection of, 114
complexity of, 116
examination by the electrical method, 118
effect of, on a fluorescent screen, 119
charge carried by the, 120 _et seq._
electrostatic deviation of, 124
velocity of, and value of _e_/_m_ for, 126
variation of _e_/_m_ with velocity of, 127 _et seq._
distribution of velocity amongst β particles, 131
absorption of, 134 _et seq._
variation of absorption with density, 136 _et seq._
number of β particles stopped by matter, 137 _et seq._
variation of intensity of, with thickness of layer, 140
secondary β rays, 189 _et seq._
relative ionization produced by α and β rays, 196
relative energy emitted in form of α and β rays, 196 _et seq._
phosphorescent action of, 201 _et seq._
physical action produced by, 207 _et seq._
chemical action of, 213
physiological action of, 216
from Ur X, 347
from active deposit of radium, 377 _et seq._
significance of appearance of, only in last radio-active changes, 455
change of weight due to expulsion of, 473

Barium platinocyanide
phosphorescence of, under radium rays, 203
change of colour due to radium rays, 205

Barkla
polarization of X rays, 80

Barnes and Rutherford
heating effect of radium emanation, 421, 429
connection of heating effect with radio-activity, 421
heating effect of active deposit, 425
heating effect of γ rays, 429
heating effect of emanation, 431
division of heating effect among active products, 433

Bary
phosphorescence under radium rays, 202

Baskerville
activity of thorium, 29
phosphorescence of kunzite under radium rays, 203

Baskerville and Kunz
phosphorescence of substances under radium rays, 204

Beattie, Smolan and Kelvin
discharging power of uranium rays, 7

Becquerel
rays from calcium sulphide, 4
rays from uranium, 5 _et seq._
permanence of uranium rays, 6
discharging power of uranium rays, 6
magnetic deflection of radium rays by photographic method, 114 _et
seq._
curvature of radium rays in a magnetic field, 115 _et seq._
complexity of radium rays, 116 _et seq._
electrostatic deflection of β rays of radium, 124 _et seq._
value of _e_/_m_ for β rays of radium, 126 _et seq._
magnetic deviation of α rays of radium and polonium, 145
trajectory of rays of radium in magnetic field, 148
scintillations due to cleavage of crystals, 160
γ rays from radium, 179
secondary rays produced by active substances, 187
phosphorescence produced by radium rays, 201
conductivity of paraffin under radium radiation, 210
effect of temperature on uranium rays, 210
chemical action of radium rays, 214
removal of activity from uranium by precipitation with barium, 219
theory of radio-activity, 438

Bemont et M. et Mme Curie
discovery of radium, 13

Berndt
spectrum of polonium, 23

Blanc
thorium in sediments from hot springs, 514

Blythswood, Lord and Allen, H. S.
radium emanation in Bath springs, 513

Bödlander and Runge
evolution of gases from radium, 215

Boltwood
origin of radium, 460
amount of radium in minerals, 460
proportionality of uranium and radium in minerals, 461
production of lead by uranium, 484
radium emanation in spring water, 514
method of standardization of amount of emanation in waters, 514

Boys
rate of dissipation of charge, 531

Bragg and Kleeman
theory of absorption of α rays, 172 _et seq._
relation between ionization and absorption, 174 _et seq._
range of α rays in air, 174
four sets of α rays from radium, 174 _et seq._

Bronson
use of steady deflection method with an electrometer, 104
decay of thorium emanation, 242
decay of excited activity from actinium, 312

Brooks, Miss
variation of excited activity from thorium for short exposures, 304
effect of dust on distribution of excited activity, 305
decay curves of excited activity of radium measured by α and β rays,
307 _et seq._
decay curves of excited activity from actinium, 312

Brooks and Rutherford
absorption of α rays by matter, 161
comparison of absorption of α rays from radio-elements, 164
diffusion of radium emanation, 270
decay of excited activity from radium, 306

Bumstead
presence of thorium emanation in atmosphere, 512

Bumstead and Wheeler
diffusion of radium emanation, 273
emanation from surface water and the soil, 512, 522
identity of emanation from soil with radium emanation, 512, 522

Burton
radium emanation in petroleum, 516

Burton and McLennan
penetrating radiation from the earth, 520
radio-activity of ordinary materials, 537
emanation from ordinary matter, 538

Campbell
radio-activity of ordinary materials, 540

Canal rays
discovery of, 78
magnetic and electric deflection of, 78
value of _e_/_m_ for, 78
similarity of, to α rays, 110

Capacity
of electroscopes, 87
of electrometers, 94, 102
standards of, 102

Carbonic acid
radio-activity of natural, 516

Caspari and Aschkinass
action of radium rays on microbes, 216

Cathode rays
discovery of, 73
magnetic and electric deflection of, 74
value of _e_/_m_ for, 75
radiation of energy from, 79
comparison of, with β rays, 120
absorption of, by matter, 136, 137
_see also_ β rays

Caves
radio-active matter present in air of, 514 _et seq._
radio-activity of air of, due to emanation from the soil, 515

Changes
(_see_ Transformations)

Charge
carried by the ions, 50 _et seq._
negative charge carried by β rays, 120
measurement of charge carried by β rays, 121 _et seq._
positive charge carried by α rays, 145
measurement of charge carried by α rays, 151 _et seq._

Chemical nature
of emanation, 267
of active deposit, 312

Chemical actions of radium rays
production of ozone, 213
coloration of glass and rock-salt, 213
on phosphorus, 214
on iodoform, 214
on globulin, 214
evolution of hydrogen and oxygen, 215

Child
potential gradient between electrodes, 65
variation of current with voltage for surface ionization, 66

Clouds
formation of, by condensation of water round ions, 46 _et seq._
difference between positive and negative ions in formation of, 49

Collie and Ramsay
spectrum of emanation, 292

Collision
ionization by, 39, 57
number of ions produced by β rays per cm. of path, 434
total number of ions produced by collisions of α particles, 434

Coloration
of crystals of radiferous barium, 15
of bunsen flame by radium, 15
of glass by radium rays, 213
of rock-salt, fluor-spar and potassium sulphate by radium rays, 213

Concentration
of excited activity on negative electrode, 297
activity of radium independent of, 466

Condensation
of water round the ions, 46 _et seq._
of emanations, 277
experimental illustration of, 279
temperature of, 280
difference between point of, for emanations of thorium and radium,
283
from air sucked up from the earth, 510

Conductivity
of gases exposed to radiations, 31 _et seq._
variation of, with pressure, 61 _et seq._
variation of, with nature of gas, 64
comparison of, for gases exposed to α, β, and γ rays, 64
comparison of, when exposed to γ rays and to hard X rays, 184
of insulators, 209
of air in caves and cellars, 507 _et seq._
of air in closed vessels, 531 _et seq._
variation of, in closed vessels with pressure and nature of gas, 534
variation of, with temperature for air in closed vessels, 536
increase of, with time, in a closed vessel, 537

Conservation of radio-activity
examples of, 469 _et seq._

Cooke, H. L.
penetrating rays from the earth, 520
number of ions per c.c. in closed vessels, 534
radio-activity from ordinary matter, 536

Cooke, W. T. and Ramsay
radio-activity produced by radiations of radium, 472

Corpuscle
(_see_ Electron)

Crookes, Sir W.
spectrum of radium, 17
spectrum of polonium, 23
nature of cathode rays, 73
nature of α rays, 142
scintillations produced by radium, 158
spinthariscope, 158
number of scintillations independent of pressure and temperature, 159
phosphorescence of diamond, 204
separation of Ur X, 219
theory of radio-activity, 441

Crookes and Dewar
absence of nitrogen spectrum in phosphorescent light of radium at low
pressures, 206

Crystallization
effect of, on activity of uranium, 349

Curie, Mme
permanence of uranium rays, 6
discovery of radio-activity of thorium, 10
radio-activity of uranium and thorium minerals, 11
relative activity of compounds of uranium, 12
coloration of radium crystals, 15
spectrum of radium, 16
discovery of polonium, 22
nature of a rays, 142
absorption of α rays from polonium, 163
secondary radiation tested by electric method, 188
slowly decaying excited activity from radium, 311
recovery of activity of radium, 375
bismuth made active by solution of barium, 417

Curie, P.
magnetic deviation of radium rays by electric method, 114
conductivity of dielectrics under radium rays, 209
radio-activity of radium unaffected by temperature, 210
decay of activity of radium emanation, 247
discovery of excited radio-activity from radium, 295
heat emission of radium at low temperature and variation of heat
emission with age of radium, 419
nature of the emanation, 439

Curie, M. et Mme
discovery of radium, 13
charge carried by β rays, 121
luminosity of radium compounds, 205
production of ozone by radium rays, 213
coloration of glass by radium rays, 213
theory of radio-activity, 439
possible absorption by radio-elements of unknown radiations, 442

Curie, J. et P.
quartz piezo-électrique, 105 _et seq._

Curie, P. et Danne
diffusion of radio-active emanation, 272
decay of excited activity from radium, 309
decay curves of radium and equation, 309
occlusion of radium emanation in solids, 310
changes in radium, 381
effect of temperature on active deposit, 390

Curie, P. and Debierne
evolution of gas from radium, 215
active gases evolved from radium, 251
phosphorescence produced by radium emanation, 252
distribution of luminosity, 252
rate of production of emanation independent of pressure, 266
effect of pressure on amount of excited activity, 266, 317

Curie and Dewar
production of helium by radium, 479

Curie, P. and Laborde
heat emission of radium, 419
origin of heat from radium, 440
radium emanation in waters of hot springs, 514

Current
through gases, 31 _et seq._
variation of, with distance between the plates, 59 _et seq._
variation of, with pressure of gas, 61 _et seq._
variation of, with nature of gas, 64
measurement of, by galvanometer, 84
measurement of, by electroscope, 85 _et seq._
measurement of, by electrometer, 90 _et seq._
measurement of, by quartz piezo-électrique, 105

Dadourian
presence of thorium emanation in the earth, 512

Danne
on deposit of radium not containing uranium, 465

Danne et Curie
diffusion of radio-active emanation, 272
decay of excited activity from radium, 309
decay curves of radium and equation, 309
occlusion of radium emanation in solids, 310
changes in radium, 381
effect of temperature on active deposit, 390

Danysz
action of radium rays on skin, 216

Darwin, G. H.
age of sun, 492

Debierne
actinium, 21
emanation from actinium, 249
decay of excited activity from actinium, 311
effect of magnetic field on activity excited from actinium, 324
barium made active by actinium, 417

Debierne and Curie
evolution of gas from radium, 215
active gases evolved from radium, 251
phosphorescence produced by radium emanation, 252
distribution of luminosity, 252
rate of production of emanation independent of pressure, 266
effect of pressure on amount of excited activity, 266, 317

Decay
of activity of Th X, 221
of activity of Ur X, 223
significance of law of, 229
effect of conditions on the rate of, 232
of activity of thorium emanation, 241
of activity of radium emanation, 247
of activity of actinium emanation, 249
of excited activity due to thorium for long exposure, 302
of excited activity due to thorium for short exposure, 304
of excited activity due to radium, 306 _et seq._
excited activity of slow decay due to radium, 311
of excited activity from actinium, 311
of radium A, B and C, 377 _et seq._
of radium D, E and F, 397 _et seq._
of heating effect of emanation, 423
of excited activity from atmosphere, 502
of activity of rain and snow, 506
of emanation from the earth, 508
differences in, of excited activity from atmosphere, 521 _et seq._

Demarçay
spectrum of radium, 16

Deposit, active
connection of, with excited activity, 301
physical and chemical properties of, 312
electrolysis of, 313
effect of temperature on, 315
effect of pressure on distribution of, 317
transmission of, by positive carriers, 318 _et seq._
nomenclature of, 328
theory of changes in, 331 _et seq._
theory of activity due to, 337 _et seq._
theory of rayless change in, 341 _et seq._
of thorium, 302 _et seq._, 351 _et seq._
analysis of, 351
rayless change in, 352
effect of temperature on, 354
period of products of, 355
of actinium, 311 _et seq._
decay curves of, 311
analysis of, 367
rayless change in, 367
period of products of, 368
radiations from, 368
of radium, 376 _et seq._
connection of excited activity with, 306
general analysis of, 376 _et seq._
analysis of, of rapid change, 377 _et seq._
analysis of α ray curves, 377
α ray curves of, 378
β ray curves of, 379
analysis of β ray curves, 381
equations of activity curves, 389
effect of temperature on, 390
volatility of, 391
of slow transformation, 311, 397
variation of α ray activity of, 398
variation of β ray activity of, 399
separation of constituents of, 401 _et seq._
successive products in, 402
variation of activity of, for long periods, 407
presence in old radium, 408
effect of, on variation of activity of radium with time, 409
presence in pitchblende, 410
connection with radio-tellurium, 411
connection with polonium, 411, 412
connection with radio-lead, 413
connection of, with radio-active induction, 415 _et seq._
heat emission of, 425 _et seq._
use of, to determine number of β particles from radium, 435
use of, as source of α rays, 543

Des Coudres
magnetic and electric deviation of α rays, 148
determination of _e_/_m_ for α rays, 148

Dewar
emission of heat from radium in liquid hydrogen, 420

Dewar and Crookes
absence of nitrogen spectrum in phosphorescent light of radium at low
pressures, 206

Dewar and Curie
production of helium by radium, 479

Dielectrics
condition of, under radium rays, 209

Diffusion
of ions, 51 _et seq._
of radium emanation into gases, 270
of thorium emanation into gases, 275
of radium emanation into liquids, 276

Discharge
action of rays on spark and electrodeless, 208

Disintegration
account of theory of, 234, 325, 445
list of products of, 449
rate of, in radio-elements, 457
emission of energy in consequence of, 474 _et seq._
helium a product of, 476 _et seq._
possible causes of, 486 _et seq._
of matter in general, 496 _et seq._

Dissipation of charge
in caves and cellars, 514 _et seq._
in closed vessels, 531
effect of pressure and nature of gas on, 534 _et seq._
effect of material of vessel on, 536 _et seq._

Dolezalek
electrometer, construction of, 94 _et seq._

Dorn
charge carried by β rays, 122
electrostatic deflection of β rays from radium, 124
discovery of radium emanation, 246
effect of moisture on emanating power of thorium, 255
electrolysis of radium solution, 313
loss of weight of radium, 474
radium emanation in springs, 513

Dreyer and Salomonsen
coloration of quartz by radium rays, 213

Dunston
analysis of thorianite, 486

Durack
ionization by collision of electrons of great velocity, 171

Dust
effect of, on recombination of ions, 42
effect of, on distribution of excited activity, 305

Earth
amount of radium in, 493 _et seq._
age of, 496
excited activity deposited on, 504
activity concentrated on peaks of, 504
emanation from, 507
very penetrating radiation from, 520

Ebert
condensation of emanation from the earth, 510
apparatus for determining number of ions per c.c. in air, 527
velocity of ions in air, 528

Ebert and Ewers
emanation from the earth, 508

Electrolysis
separation of radio-tellurium by, 25
of solutions of active deposit, 313
of radium solutions, 313
of thorium solutions, 314

Electrometer
description of, 90 _et seq._
use of, in measurements, 90
construction of, 91 _et seq._
Dolezalek, 94
adjustment and screening of, 95
special key for, 97
application of, to measurements of radio-activity, 97 _et seq._
measurement of current by, 100
capacity of, 101
use with steady deflection, 103
use with quartz piezo-électrique, 105

Electron
definition of, 56
production of, under different conditions, 76 _et seq._
identity of β rays with electrons, 120 _et seq._
variation of apparent mass of electron with velocity, 127 _et seq._
evidence that mass of electron is electromagnetic, 129 _et seq._
diameter of, 131

Electroscope
description of, used by Curie, 85
construction of, for accurate measurements, 86
use of, in measurements of minute currents, 86
of C. T. R. Wilson, 89
use of, in measuring conductivity of air in closed vessels, 531 _et
seq._
use of, for determining radio-activity of ordinary matter, 537

Elster and Geitel
radio-active lead, 27
effect of magnetic field on conductivity produced in air by β rays,
113
scintillations produced by active substances, 158
action of radium rays on spark, 208
photo-electric action of body, coloured by radium rays, 214
radio-active matter in earth, 494
discovery of excited activity in atmosphere, 501
emanations from the earth, 507
radio-activity of air in caves, 507
radio-activity of the soil, 515
radio-activity of fango, 516
variation of radio-activity in atmosphere with meteorological
conditions, 517
effect of temperature and pressure on atmospheric radio-activity, 518

Emanation
of thorium, discovery and properties of, 238
methods of measurement of, 240
decay of activity of, 241
effect of thickness of layer on amount of, 243
increase of, with time to a maximum, 245
of radium, 246
decay of activity of, 247
of actinium, properties of, 249
of radium, phosphorescence produced by, 251
rate of emission of, 254
effect of conditions on rate of emission of, 255
regeneration of emanating power, 256
continuous rate of production of, 257
source of thorium emanation, 261
source of radium and actinium emanation, 263
radiations from, 263
effect of pressure on production of, 265
chemical nature of, 267
experiments to illustrate gaseous nature of, 268
rate of diffusion of radium emanation, 269
rate of diffusion of thorium emanation, 275
diffusion of, into liquids, 276
condensation of, 277
temperature of condensation of, 280
volume of, from one gram of radium and thorium, 288
measurement of volume of, from radium, 289
diminution of volume of, 290
spectrum of emanation, 292
connection between emanation and excited activity, 298
effect of removal of, on activity of radium, 371 _et seq._
fraction of activity of radium due to, 374
effect of rate of escape of, on activity of radium, 374
heat emission of, 420, 431
variation of heat emission with time, 421 _et seq._
enormous emission of energy from emanation, 431
radio-activity of atmosphere due to emanations, 504
sucked up from the earth, 507
in caves, 507 _et seq._
rate of decay of activity of, from the earth, 508
condensation of, from the atmosphere, 510
in well water and springs, 510 _et seq._
from “fango,” 516
effect of meteorological conditions on amount of, in atmosphere, 517
_et seq._
from metals, 538

Emanating power
measurement of, 254
effect of conditions on, 255
regeneration of, 256

Emanium or “emanating substance” of Giesel (_see_ Actinium)
discovery of, 21
separation and properties of, 21
similarity of, to actinium, 21
emanation from, 249
excited activity produced by, 311
action of an electric field on, 323

Energy
of α particle, 156
of β particle, 196
comparison of, for α and β particles, 196
emitted from radium in form of heat, 419 _et seq._
emission of, from the emanation, 431
emission of, from radio-active products of radium, 433
total emission of, from 1 gram of radio-elements, 474 _et seq._
latent store of, in matter, 475

Eve
conductivity of gases exposed to X rays, 64
conductivity of gases exposed to X rays and γ rays, 183, 184
secondary rays produced by β and γ rays, 189 _et seq._
magnetic deflection of secondary rays from γ rays, 193
variation of activity of radium with concentration, 467
amount of radium emanation in the atmosphere, 524 _et seq._
ionization due to emanation in atmosphere, 526 _et seq._

Evolution of matter
evidence of, 497

Ewers and Ebert
emanation from the earth, 508

Excited radio-activity
discovery and properties of, 295 _et seq._
concentration of, on negative electrode, 297
connection of, with the emanations, 298
removal of, by acids, 300
decay of, due to thorium, 302
decay of, for short exposure to thorium, 304
effect of dust on distribution of, 305
decay curves for different times of exposure, 306 _et seq._
decay of, from radium, 306
decay curves of, measured by α rays, 308
decay curves of, measured by β rays, 309
decay curves of, from actinium, 311
of radium, of very slow decay, 311
effect of solution on, 312
electrolysis of active solutions, 313
effect of temperature on, 315
variation with electric field, of amount of, 316
effect of pressure on distribution of, 317
transmission of, 318
from actinium and emanium, 323
heat emission due to, 425 _et seq._
from the atmosphere, 501 _et seq._
decay of, 502
due to emanation in atmosphere, 504
distribution of, on surface of the earth, 504
concentration of, on prominences of the earth, 504
of rain and snow, 506
produced by emanation from tap water, 510
effect of meteorological conditions on amount of, 517 _et seq._
amount of, at Niagara Falls, 520
rate of decay of, dependent on conditions, 522 _et seq._

Exner and Haschek
spectrum of radium, 17

Eye
action of radium rays on, 217

Fehrle
distribution of excited activity on a plate in electric field, 318

Fluorescence
produced in substances by radium rays, 18
produced in substances by radium and polonium rays, 201 _et seq._

Fog
large amount of excited activity during, 518

Forch
loss of weight of radium, 474

γ rays
relative conductivity of gas exposed to γ and hard X rays, 64, 184
discovery of, 179
absorption of, by matter, 179 _et seq._
connection between absorption of, and density, 182
discussion of nature of rays, 182 _et seq._
secondary rays produced by γ rays, 189
measurement of radio-activity by means of, 442, 467
conservation of radio-activity measured by, 471

Gases
evolved by radium, 215
presence of helium in gases from radium, 216

Gates, Miss F.
effect of temperature on excited activity, 315
discharge of quinine sulphate, 530

Geitel
natural conductivity of air in closed vessels, 501, 531

Geitel and Elster
radio-active lead, 27
effect of magnetic field on conductivity produced by radium rays, 113
scintillations produced by active substances, 158
action of radium rays on spark, 208
photo-electric action of bodies coloured by radium rays, 214
radio-active matter in earth, 494
discovery of radio-active matter in atmosphere, 501
emanations from the earth, 507
radio-activity of air in caves, 507
radio-activity of the soil, 515
radio-activity of fango, 516
variation of radio-activity of air with meteorological conditions,
517
effect of temperature and pressure on radio-activity in atmosphere,
518

Giesel
coloration of bunsen flame by radium, 15
separation of radium by crystallization of bromide, 15
emanating substance, 21
radio-active lead, 27
magnetic deviation of β rays, 113
decrease with time of luminosity of radio-active screen, 205
spectrum of phosphorescent light of emanium due to didymium, 206, 207
coloration of bodies by radium rays, 213
evolution of gases from radium, 215
action of radium rays on the eye, 217
emanation from the emanating substance, 250
luminosity produced by radium emanation, 251
decay of excited activity of emanium, 312
activity of radium dependent on age, 371
bismuth made active by radio-active solution, 417
temperature of radium bromide above air, 420

Gimingham and Rossignol
decay of thorium emanation, 242

Glass
coloration produced in, by radium rays, 213
phosphorescence produced in, by emanation, 252

Glew
simple form of spinthariscope, and scintillations, 159

Globulin
action of radium rays on, 214

Godlewski
effect of crystallization on activity of uranium, 349
diffusion of uranium X, 350
separation of actinium X, 365
source of actinium emanation, 365
recovery and decay curves of actinium, 366
penetrating power of β and γ rays from actinium, 368
radiations from active products, 368

Goldstein
canal rays, 78
coloration of bodies by radium rays, 213

Gonder, Hofmann, and Wölfl
properties of radio-active lead, 27, 413

Grier and Rutherford
magnetic deviation of β rays of thorium, 114
relative current due to α and β rays, 195
nature of rays from Ur X, 347

Hardy
coagulation of globulin by radium rays, 214

Hardy and Miss Willcock
coloration of iodoform solutions by radium rays, 214

Hardy and Anderson
action of radium rays on the eye, 217

Harms
number of ions per c.c. in closed vessel, 534

Hartmann
spectrum of phosphorescent light of emanium, 206

Haschek and Exner
spectrum of radium, 17

Heat
rate of emission of, from radium, 419 _et seq._
emission of, from radium at low temperatures, 420
connection of heat emission with the radio-activity, 421 _et seq._
source of heat energy, 421 _et seq._
rate of emission of, after removal of the emanation, 422 _et seq._
rate of emission of, by emanation, 423, 431
variation with time of heat emission of radium, and of its emanation,
423
heating effect of the emanation, 423, 431
heating effect of active deposit, 425
proportion of heating effect due to radio-active products, 433
origin of, in radium, 442 _et seq._
total heat emission during life of radio-elements, 474 _et seq._
heating of earth by radio-active matter, 493

Heaviside
apparent mass of moving charged body, 71, 127

Helium
produced by radium and its emanation, 476 _et seq._
amount of, from radium, 480
origin of, 480

Helmholtz and Richarz
action of ions on steam jet, 47

Hemptinne
action of rays on spark and electrodeless discharge, 208

Henning
resistance of radium solutions, 208
effect of voltage on amount of excited activity, 316

Henning and Kohlrausch
conductivity of solutions of radium bromide, 208

Hertz
electric deviation of cathode rays, 73

Heydweiler
loss of weight of radium, 474

Himstedt
action of radium rays on selenium, 208
radium emanation in springs of Baden, 513

Himstedt and Meyer
production of helium by radium, 479

Himstedt and Nagel
action of radium rays on the eye, 217

Hofmann, Gonder, and Wölfl
properties of radio-active lead, 27, 413

Hofmann and Strauss
radio-active lead, 27

Hofmann and Zerban
connection of activity of thorium with uranium, 29

Huggins, Sir W. and Lady
spectrum of phosphorescent light of radium bromide, 205

Hydrogen
production of, by radium rays, 215

Induced radio-activity (_see_ Excited radio-activity)

Induction
radio-active, 24
meaning and examples of, 415 _et seq._

Insulators
conduction of, under radium rays, 209

Iodoform
coloration produced in, by radium rays, 214

Ionization
theory of, to explain conductivity of gases, 31 _et seq._
by collision, 39, 57
variation of, with pressure of gas, 61 _et seq._
variation of, with nature of gas, 64
comparison of, produced by rays, 111, 194
production of, in insulators, 209
total, produced by 1 gram of radium, 433 _et seq._
natural ionization of gases, 531 _et seq._
connection of, with phosphorescent and photographic actions, 549

Ions
in explanation of conductivity of gases, 31 _et seq._
production of, by collision, 39, 57
rate of recombination of, 40 _et seq._
mobility of, 42 _et seq._
difference between mobility of positive and negative, 43 _et seq._
condensation of water around, 46 _et seq._
difference between positive and negative, 49
charge carried by, 50
diffusion of, 51 _et seq._
charge on an ion same as on hydrogen atom, 54
number of, produced per c.c., 54
size and nature of, 55 _et seq._
definition of, 56 _et seq._
velocity acquired by, between collisions, 58
energy required to produce, 58, 551
comparative number of, produced in gases, 65
disturbance of potential gradient by movement of, 65
production of, in insulators, 209
number of, produced by α particle, 433
number produced per c.c. in closed vessels, 533 _et seq._

Joly
motion of radium in an electric field, 211
absorption of radium rays by atmosphere, 492 (see foot-note)

Kaufmann
velocity of cathode rays, 75
variation of _e_/_m_ with velocity of electron, 127 _et seq._

Kelvin
theory of radio-activity, 441
age of sun and earth, 492, 493

Kelvin, Smolan and Beattie
discharging power of uranium rays, 7

Kleeman and Bragg
theory of absorption of α rays, 172 _et seq._
relation between ionization and absorption, 174 _et seq._
range of α rays in air, 174
four sets of α rays from radium, 174 _et seq._

Kohlrausch
conductivity of water altered by radium rays, 208

Kohlrausch and Henning
conductivity of solutions of radium bromide, 208

Kunz
phosphorescence of willemite and kunzite, 203

Kunz and Baskerville
phosphorescence of substance under radium rays, 204

Kunzite
phosphorescence of, under radium rays, 203

Laborde and Curie
heat emission of radium, 419
origin of heat from radium, 440
radium emanation in waters of hot springs, 514

Langevin
coefficient of recombination of ions, 41
velocity of ions, 45 _et seq._
energy required to produce an ion, 58
secondary radiation produced by X rays, 187
slow moving ions in air, 528

Larmor
radiation theory, 77
radiation of energy from moving electron, 79
structure of the atom, 157

Lead, radio-active
preparation of, 26
radiations from, 26

Le Bon
rays from bodies exposed to sunlight, 5
discharging power of quinine sulphate, 9, 530

Lenard
ionization of gases by ultra-violet light, 9
action of ions on a steam jet, 47
penetrating power of cathode rays, 73
negative charge carried by Lenard rays, 120
absorption of cathode rays proportional to density, 136, 137

Lerch, von
chemical properties of active deposit of thorium, 313
electrolysis of solution of active deposit, 313
effect of temperature on excited activity, 315
temporary activity of active deposit from thorium, 415

Lockyer
inorganic evolution, 499

Lodge, Sir Oliver
electronic theory, 69
instability of atoms, 487

Lorentz
structure of atoms, 157

Lowry and Armstrong
radio-activity and phosphorescence, 444

Luminosity
of radium compounds, 205
change of, in radium compounds with time, 205
spectrum of phosphorescent light from radium bromide, 206
of radium compounds unaffected by temperature, 210

Mache
radium emanation in hot springs, 513

Mache and von Schweidler
velocity of ions in air, 528

Makower
diffusion of radium emanation, 274
diffusion of thorium emanation, 276

Marckwald
preparation of radio-tellurium, 25
rate of decay of radio-tellurium, 411

Mass
apparent mass of electron, 71, 127
variation of mass of electron with speed, 127 _et seq._
of α particle, 147 _et seq._

Materials
radio-activity of ordinary, 528, 536 _et seq._

Matteucci
rate of dissipation of charge in closed vessels, 531

McClelland
absorption of γ rays, 181
secondary rays from β and γ rays from radium, 192

McClung
coefficient of recombination of ions, 41
conductivity of gases exposed to X rays, 64
ionization by α rays from radium C, 550

McClung and Rutherford
energy required to produce an ion, 58
variation of current with thickness of layer of uranium, 195
estimate of energy radiated from radio-elements, 418
radiation of energy from radium, 438

McLennan
absorption of cathode rays, 65
radio-activity of snow, 506
excited radio-activity at Niagara Falls, 519

McLennan and Burton
penetrating radiation from the earth, 520
radio-activity of ordinary materials, 537
emanation from ordinary matter, 538

Metabolon
definition of, 446
table of metabolons, 449
radio-elements as metabolons, 457

Meteorological conditions
effect of, on radio-activity of atmosphere, 517

Methods of measurement
in radio-activity, 82 _et seq._
comparison of photographic and electrical, 83 _et seq._
description of electrical, 84 _et seq._

Meyer and Himstedt
production of helium by radium, 479

Meyer and Schweidler
magnetic deviation of β rays by electrical method, 113
absorption of β rays of radium by matter, 136
activity proportional to amount of uranium, 195
emanation from uranium, 348
effect of crystallization on activity of uranium, 349
rate of decay of radio-tellurium, 411

Minerals, radio-active
constant ratio of radium to uranium, 459 _et seq._
list of minerals, 461
age of, 485
composition of, 554 _et seq._

Mobility
of ions, 43 _et seq._

Moisture
effect of, on velocity of ions, 43, 45
effect of, on emanating power, 255

Molecule
number of, in 1 c.c. of hydrogen, 54

Molecular weight
of radium emanation, 273
of thorium emanation, 275

Nagel and Himstedt
action of radium rays on the eye, 217

Niewenglowski
rays from sulphide of calcium, 4

Nomenclature
of successive products, 328 _et seq._

Number
of molecules per c.c. of hydrogen, 54
of ions produced in gas by active substances, 55
of β particles expelled from 1 gram of radium, 124
of α particles emitted per gram of radium, 155
of ions produced per c.c. in closed vessels, 534

Occlusion
of emanation in thorium and radium, 258
of radium emanation by solids, 310

Owens
saturation current affected by dust, 42
penetrating power of rays independent of compound, 164
absorption of α rays varies directly as the pressure of gas, 169
effect of air currents on conductivity produced by thorium, 238

Oxygen
change into ozone, by radium rays, 213
production of, from radium solutions, 215

Ozone
production of, by radium rays, 213

Paraffin
objection to, as an insulator, 96
conductivity of, under radium rays, 210

Paschen
distribution of velocity amongst β particles, 131 _et seq._
absence of magnetic deflection of γ rays, 183
γ rays and electrons, 185
heating effect of γ rays, 186, 429

Patterson
number of ions per c.c. in closed vessel, 534
natural conductivity of air due to an easily absorbed radiation, 536
effect of temperature on natural conductivity of air, 536

Peck and Willows
action of radium rays on spark, 208

Pegram
electrolysis of thorium solutions, 314
temporary activity of substances separated from thorium, 415

Penetrating power
comparison of, for α, β and γ rays, 111
variation in, of β rays, 134 _et seq._
variation of, with density for β rays, 137
comparison of, for α rays from radio-elements, 164
variation of, with density for α rays, 169
variation of, with density for γ rays, 182

Penetrating radiation
from the earth and atmosphere, 520

Perrin
charge carried by cathode rays, 73
theory of radio-activity, 437

Phosphorescence
production of, by radium, 19
production of, by radium and polonium rays, 201 _et seq._
comparison of, produced by α and β rays, 202
of zinc sulphide, 202
of barium platinocyanide, 203
of willemite and kunzite, 203
produced by radium emanation in substances, 203, 252
diminution of, with time, 205
of radium compounds, 205
spectrum of phosphorescent light of radium bromide, 205
spectrum of phosphorescent light of “emanium,” 206
production of by heat (thermo-luminescence), 207
use of, to illustrate condensation of emanations, 279
connection of with ionization, 547 _et seq._

Phosphorus
action of radium rays on, 214
ionization produced by, 529

Photo-electric action
produced by radium rays in certain substances, 214

Photographic
method, advantages and disadvantages of, 83
relative photographic action of rays, 83
connection of photographic action with ionization, 546

Physical action of radium rays
on sparks, 208
on electrodeless discharge, 208
on selenium, 208
on conductivity of insulators, 209

Physiological action of radium rays
production of burns, 216
effect on bacteria, 216
effect on eye, 217

Piezo-électrique of quartz
description of, 105

Pitchblendes
comparison of radio-activity of, 11
radio-elements separated from, 13 _et seq._
radium continually produced from, 459
constitution of, 557

Polarization of uranium rays
absence of, 7

Polonium
methods of separation of, 22
rays from, 23
decay of activity of, 23
discussion of nature of, 24
similarity to radio-tellurium, 26
magnetic deviation of α rays from, 146, 150
slow moving electrons, 153
increase of absorption with thickness of matter traversed, 163
connection of, with radium F, 411

Potential
required to produce saturation, 32 _et seq._
fall of potential needed to produce ions at each collision, 58
gradient due to movement of ions, 65

Precht and Runge
spectrum of radium, 17
atomic weight of radium, 18
heating effect of radium, 420

Pressure
effect of, on velocity of ions, 46
effect of, on current through gases, 61 _et seq._
production of emanation independent of, 265
effect of, on distribution of excited activity, 317
effect of, on natural conductivity of air in closed vessels, 534

Products, radio-active
list of, from radio-elements, 449
properties of, 449
amount of in radium, 452 _et seq._
radiations from, 455

Quartz piezo-électrique
use of, in measurement of current, 105

Quinine sulphate
discharging power of, 530
phosphorescence of, 530

Radiations
emitted by uranium, 8
emitted by thorium, 10
emitted by radium, 18
emitted by actinium, 21
emitted by polonium, 23
method of measurement of, 82 _et seq._
methods of comparison of, 108
three kinds of, 109
analogy to rays from a Crookes tube, 110
relative ionizing and penetrating power of, 111
difficulties of comparative measurement of, 112
β rays, 113
α rays, 141
γ rays, 179
secondary rays, 187
comparison of ionization of α and β rays, 194
phosphorescent effect of, 201 _et seq._
physical actions of, 207 _et seq._
chemical actions of, 213 _et seq._
physiological actions of, 216
from the emanation, 263
from Ur X, 347
connection of, with heat emission, 421 _et seq._
from different active products, 455
conservation of energy of each specific type of, 469 _et seq._

Radio-lead
connection of, with polonium, 411 _et seq._
connection of, with radium D, 413

Radio-tellurium
rate of decay of, 411
connection of with radium F, 411

Radium
discovery of, 13
separation of, 13
spectrum of, 16
atomic weight of, 17
radiations from, 18
compounds of, 19
nature of radiations from, 109
β rays from, 113
α rays from, 141
γ rays from, 179
secondary rays from, 187
production of phosphorescence by, 201 _et seq._
spectrum of phosphorescent light of, 206
physical actions of, 207 _et seq._
chemical actions of, 213 _et seq._
physiological actions of, 216
emanation from, 246
properties of emanation from, 247 _et seq._
chemical nature of emanation from, 267
diffusion of emanation from, 269
condensation of emanation from, 277
amount of emanation from, 288
volume of emanation from, 289
spectrum of emanation from, 292
excited radio-activity from, 295 _et seq._
decay of excited activity from, 306 _et seq._
difference in properties of radium and the emanation, 327
nomenclature of products, 328
theory of successive changes in, 330
alteration of activity of, by removal of emanation, 371 _et seq._
recovery of activity of, after removal of emanation, 372
effect of escape of emanation on recovery of activity of, 374
non-separable activity of, 375
period and properties of radium A, B and C, 376 _et seq._
analysis of active deposit of rapid changes of radium, 377
analysis of β ray curves, 381 _et seq._
analysis of α ray curves, 386 _et seq._
equations of activity curves, 389
effect of temperature on active deposit of, 390
relative activity due to products of, 395
active deposit of slow transformation, 397
physical and chemical properties of radium D, E and F, 398 _et seq._
effect of temperature on active deposit of slow change, 401
separation of radium F by bismuth, 402
products of, 402 _et seq._
rate of transformation of radium D, 404 _et seq._
variation of the activity of the active deposit over long periods of
time, 407
amounts of radium D, E and F in old radium, 408
variation of activity of, with time, 409
products of in pitchblende, 410
origin of radio-tellurium, 411
origin of polonium, 411, 412
origin of radio-lead, 413
temporary activity of inactive matter separated from pitchblende, 415
_et seq._
heat emission of, 419 _et seq._
heat emission of emanation from, 420, 431
heating effects due to products of, 433
theories of radio-activity of, 437 _et seq._
discussion of theories of radio-activity of, 441 _et seq._
energy of radiations, not derived from external source, 442 _et seq._
theory of radio-active change, 444 _et seq._
list of active products of, 449
amount of products of, 452
rate of change of, 457
life of radium, 457
origin of, 459 _et seq._
production of, by uranium, 459 _et seq._
amount of in 1 gram of uranium, 461
amount of, in minerals, 461
radio-activity of, independent of concentration, 466 _et seq._
disappearance of, 467
life of, independent of concentration, 468
conservation of radio-activity of, 469 _et seq._
loss of weight of, 473
experiments to determine loss of weight of, 474
total emission of energy from 1 gram of, 474 _et seq._
production of helium from, 476
helium, disintegration product of, 479 _et seq._
amount of helium from, 480
possible causes of disintegration of, 486 _et seq._
amount of, to account for heat of sun, 491
possible connection of with heat of sun, 491
possible connection of with heat of earth, 493
probable amount of, in earth, 495
amount of, in atmosphere, 495, 524
presence of, in atmosphere, 521 _et seq._

Radium A
decay curve of, 378
radiation from, 381
effect of, on activity curves, 386 _et seq._
connection with later changes, 392
activity supplied by, 393

Radium B
absence of rays in, 381
effect of, on activity curves, 381 _et seq._
effect of temperature on, 390
volatility of, 390
absence of heating effect of, 433
nature of rayless change in, 454, 552

Radium C
radiations from, 381
analysis of β ray curves of, 381 _et seq._
analysis of α ray curves of, 386 _et seq._
effect of temperature on, 390
activity supplied by, 394 _et seq._
heating effect of, 425
use of, as a source of β rays, 435
explosive nature of change in, 456
magnetic deflection of rays from, 543
velocity and value of _e_/_m_ for rays from, 544

Radium D
origin of name of, 376
connection of, with active deposit, 403
period of transformation of, 406
effect of, on variation of activity, 407
presence in old radium, 408
effect of, on activity of old radium, 409
presence in pitchblende, 410
connection with radio-lead, 413
amount of, in 1 ton of uranium, 454

Radium E
effect of temperature on, 401
connection of, with β ray activity active deposit, 403, 400
connection with radio-lead, 413

Radium F
variation of activity due to, 398
effect of temperature on, 401
separation of, on bismuth plate, 402
connection with active deposit, 403
variation of activity of, over long periods of time, 407
presence in old radium, 409
effect of, on activity of old radium, 409
presence in pitchblende, 410
connection with radio-tellurium, 411
connection with polonium, 411, 412
connection with radio-lead, 413

Rain
radio-activity of, 505
decay of activity of, 506

Ramsay, Sir W.
amount of helium in thorianite, 486

Ramsay and Collie
spectrum of emanation, 292

Ramsay and Cooke
radio-activity produced by radiation from radium, 472

Ramsay and Soddy
evolution of gas from radium, 215
production of hydrogen and oxygen from radium, 215
chemical nature of the emanation, 268
gaseous nature of the emanation, 268
volume of emanation, and change with time, 289
helium from radium emanation, 291
amount of helium produced by radium, 480

Ramsay and Travers
amount of helium in fergusonite, 486

Rayless changes
discussion of, 454, 552

Re, F.
theory of radio-activity, 441

Recombination
of ions, 40 _et seq._
constant of, 42

Recovery
of activity of thorium after removal of Th X, 221
of activity of uranium after removal of Ur X, 223
significance of law of, 224
effect of conditions on rate of, 232
of activity of radium after removal of emanation, 372
of heating effect of radium, 423

Reflection
no evidence of direct reflection for uranium rays, 7
diffuse reflection of rays, 7

Refraction
no evidence of, for uranium rays, 7

Regeneration
of emanating power, 256

Richarz and von Helmholtz
action of ions on steam jet, 47

Richarz and Schenck
theory of radio-activity, 441

Rossignol and Gimingham
decay of thorium emanation, 242

Runge
spectrum of radium, 17

Runge and Bödlander
evolution of gas from radium, 215

Runge and Precht
spectrum of radium, 17
atomic weight of radium, 18
heating effect of radium, 420

Russel
photographic action of substances, 83

Saake
amount of emanation in air at high altitudes, 519

Salomonsen and Dreyer
coloration of quartz by radium rays, 213

Saturation current
meaning of, 33 _et seq._
application of, to measurements of radio-activity, 84
measurement of, 100 _et seq._

Schenck
radium emanation in springs, 513

Schenck and Richarz
theory of radio-activity, 441

Schmidt
discovery of radio-activity of thorium, 10

Schmidt and Wiedemann
thermo-luminescence, 207

Schuster
number of ions per c.c. in air of Manchester, 528
radio-activity of matter, 529

Schweidler and Mache
velocity of ions in air, 528

Schweidler and Meyer
magnetic deviation of β rays by electrical method, 113
absorption of β rays of radium by matter, 136
activity proportional to amount of uranium, 195
emanation from uranium, 348
effect of crystallization on activity of uranium, 349
rate of decay of radio-tellurium, 411

Scintillations
discovery of, in zinc sulphide screen, 158
connection of, with α rays, 158
illustration of, by spinthariscope, 158
cause of, 160
production of, by action of electric field, 160

Searle
apparent mass of moving charged body, 71, 127

Secondary rays
examination of, by photographic method, 187
examination of, by electrical method, 188
production of, by β and γ rays, 189 _et seq._
from different materials, 191
amount of, depends upon atomic weight, 192
magnetic deflection of, 193

Seitz
absorption of electrons by matter, 137 _et seq._

Selenium
action of radium rays on, 208

Simon
value of _e_/_m_ for cathode rays, 75, 129

Simpson
amount of excited activity in north of Norway, 519

Slater, Miss
effect of temperature on active deposit of thorium, 354

Smolan, Beattie and Kelvin
discharging power of uranium rays, 7

Snow
radio-activity of, 506
decay of activity of, 507

Soddy
comparison of photographic and electrical action of uranium rays, 83
nature of rays from Ur X, 347
production of radium from uranium, 463

Soddy and Ramsay
evolution of gas from radium, 215
production of hydrogen and oxygen from radium, 215
chemical nature of the emanation, 268
gaseous nature of the emanation, 268
volume of the emanation, and change with time, 289
helium from radium emanation, 291
amount of helium produced by radium, 480

Soddy and Rutherford
separation of Th X, 220
decay of activity of Th X, 221
recovery of activity of thorium freed from Th X, 221
decay of activity of Ur X, 223
recovery of activity of uranium freed from Ur X, 223
explanation of decay and recovery curves, 224
rate of production of Th X, 227
theory of decay of activity, 229
influence of conditions on rate of decay and recovery of activity,
233
disintegration hypothesis, 234
decay of activity of radium emanation, 247
measurements of emanating power, 254
effect of temperature, moisture, and solution, on emanating power,
255
regeneration of emanating power, 256
constant rate of production of emanation of radium and thorium, 257
source of thorium emanation, 261
radiations from the emanation, 264
chemical nature of emanation, 267
condensation of emanations of radium and thorium, 277
temperature of condensation of emanation, 278
effect of successive precipitations on activity of thorium, 358
recovery of activity of radium, 372
theory of radio-activity, 439
theory of radio-active change, 445
conservation of radio-activity, 469

Soil
radio-activity of, 507 _et seq._
difference in activity of, 508 _et seq._

Solution
coloration of, by radium, 15
of active deposit in acids, 312
electrolysis of active, 313

Source
of thorium emanation, 261
of radium and actinium emanations, 263

Spark
action of radium rays on, 208

Spectrum
spark spectrum of radium, 15, 16
flame spectrum of radium, 17
effect of a magnetic field on spectrum of radium, 17
of polonium, 23
of phosphorescent light of radium bromide, 206
of emanation, 292
of helium in radium gases and emanation, 477

Spinthariscope
description of, 158

Springs
emanation from water of, 513

Stark
energy to produce an ion, 58

Stoney, Johnstone
use of term electron, 76

Strauss and Hofmann
radio-active lead, 27

Strutt
conductivity of gases for radiation, 63, 64
conductivity of gases produced by γ rays, 64, 183
negative charge carried by β rays, 122 _et seq._
absorption of β rays proportional to density, 136
nature of α rays, 142
attempt to measure charge of α rays, 153
constant ratio of uranium to radium in minerals, 462
connection of thorium with helium, 483
absorption of radium rays from sun by atmosphere, 492
presence of radium in Bath waters, 513
radio-activity of ordinary matter, 536

Sun
effect of radium in, 491
age of, 492

Temperature
effect of, on intensity of radiations from uranium and radium, 210
effect of, on luminosity, 210
rate of decay of radium emanation unaffected by, 249
of condensation of emanations, 283
rate of decay of thorium emanation unaffected by, 287
effect of, on excited activity, 315
effect of, on active deposit of thorium, 354
effect of, on active deposit of actinium, 368
effect of, on active deposit of rapid change of radium, 390
effect of, on active deposit of slow change, 401
of radium above surrounding space, 419
effect of, on amount of excited activity in atmosphere, 518
effect of, on natural ionization of air, 536

Theories
of radio-activity, review of, 437 _et seq._
discussion of, 441 _et seq._
disintegration theory, 445 _et seq._

Thermo-luminescence, 207

Thomson, J. J.
relation between current and voltage for ionized gases, 34
difference between ions as condensation nuclei, 49
charge on ion, 50
magnetic field produced by an ion in motion, 69
apparent mass of electron, 71
action of magnetic field on moving ion, 72
determination of _e_/_m_ for cathode stream, 73
origin of X rays, 80
slow velocity electrons from radio-tellurium, 153
charge carried by α rays, 154
theory of radio-activity, 440
cause of heat emission from radium, 442
structure of atom, 487
possible causes of disintegration of radium, 487
nature of electrons, 496
emanation from tap-water and deep wells, 510
radio-activity of ordinary materials, 539

Thomson, J. J. and Rutherford
ionization theory of gases, 31 _et seq._

Thorium
discovery of radio-activity of, 10
emanation from, 11
preparation of non-radio-active thorium, 29
nature of radiations from, 109
β rays from, 114
α rays from, 141
γ rays from, 180
separation of Th X from, 220
recovery of activity of, 221
disintegration of, 234
emanation from, 238
properties of emanation from, 239
diffusion of emanation from, 275
condensation of emanation from, 277
excited radio-activity from, 295 _et seq._
analysis of active deposit of, 351 _et seq._
rayless change in, 352
explanation of initial portion of decay curve, 358
explanation of initial portion of recovery curve, 358
effect of successive precipitations on, 358
recovery curve after large number of precipitations, 359
products of, 363
non-separable activity of, 363
radiations from active products of, 363
division of activity amongst active products of, 363
rate of emission of energy by, 432
theories of radio-activity of, 438
discussion of theories of radio-activity, 441 _et seq._
source of energy of radiations, 442 _et seq._
theory of radio-active change, 444 _et seq._
table of radio-active products of, 449
rate of change of, 458
life of, 458
conservation of radio-activity of, 469
total emission of energy from 1 gram of, 475
possible causes of disintegration of, 486 _et seq._

Thorium A
period and properties of, 352 _et seq._
absence of rays in, 352
effect of temperature on, 354

Thorium B
period and properties of, 352 _et seq._
effect of temperature on, 354
radiations from, 363

Thorium X
methods of separation of, 220
law of decay of activity of, 221
law of recovery of activity of, 221
theory to explain production of, 224
material nature of, 226
continuous production of, 227
explanation of decay of activity of, 229
effect of conditions on the rate of change of, 233
disintegration hypothesis to explain production of, 234
minute amount of, produced, 237
effect of successive separations of, on activity of thorium, 358 _et
seq._
analysis of decay and recovery curves of, 358
radiations from, 363

Tommasina
scintillations produced by electrification, 160

Townsend
ions by collision, 39, 57
coefficient of recombination, 41
diffusion of ions, 51 _et seq._
comparison of charge on ion with that on hydrogen atom in
electrolysis, 53
number of molecules per c.c. of gas, 54
ionization by collision for different speeds, 171

Transformations, successive
theory of, 325 _et seq._
nomenclature of, 328
activity due to, 337
detection of a rayless change in, 341
in uranium, 346 _et seq._
in thorium, 351 _et seq._
in actinium, 364 _et seq._
in radium, 371 _et seq._
list of, 449
origin of radium in, 459
helium, a result of, 476 _et seq._
possible cause of, 486 _et seq._
application of, to evolution of matter, 497 _et seq._

Transmission
of excited radio-activity of radium and thorium, 318 _et seq._
of excited radio-activity of actinium, 323

Travers and Ramsay
amount of helium in fergusonite, 486

Troost
rays from hexagonal blende, 4

Uranium
discovery of radio-activity of, 5
persistence of radiations of, 6
discharging power of rays, 7
absence of reflection, refraction and polarization, 7
examination of uranium minerals, 11 _et seq._
relative activity of compounds of uranium, 12
nature of radiations from, 109
β rays from, 114
α rays from, 141
γ rays from, 180
separation of Ur X from, 219
recovery of activity of, 219
changes in, 346 _et seq._
non-separable activity of, 347
radiations from Ur X, 347 _et seq._
method of measurement of activity of Ur X, 347
emission of energy by, 418
theories of radio-activity of, 437 _et seq._
discussion of theories of radio-activity, 441 _et seq._
source of energy of radiation, 442 _et seq._
theory of radio-active change, 444 _et seq._
table of active products, 449
rate of change of, 458
life of, 458
radium probable product of, 459 _et seq._
amount of radium in, 460 _et seq._
amount of, in radio-active minerals, 461
growth of radium in, 463
conservation of radio-activity of, 469
total emission of energy from 1 gram of, 475
possible causes of disintegration of, 486 _et seq._

Uranium X
separation of, by Crookes, 219
separation of, by Becquerel, 219
decay of activity of, 223
recovery of activity of, 223
theory to explain production of, 224 _et seq._
material nature of, 226
explanation of decay of activity of, 229
changes in, 346 _et seq._
radiations from, 347 _et seq._
method of measurement of radiations from, 347
effect of crystallization on activity of, 349
diffusion of, 350

Velocity
of ions in electric field, 42 _et seq._
difference between, of positive and negative ions, 43 _et seq._
of β particle or electron, 126 _et seq._
variation of mass of electron with, 127
of α particle, 148
of transmission of carriers of excited activity, 320 _et seq._
of ions in atmosphere, 528

Villard
discovery of γ rays from radium, 179
alteration of X ray screen with time, 205
activity produced by cathode rays, 530

Vincenti and Levi Da Zara
radium emanation in spring waters, 516

Voller
variation of activity of radium with concentration, 467

Volume
of radium emanation, calculation of, 289
decrease of, of radium emanation, 290

Walker, G. W.
theory of electrometer, 90

Walkhoff
action of radium rays on skin, 216

Wallstabe
diffusion of radium emanation into liquids, 276

Water
emanation from, 510 _et seq._
decay of activity of emanation from, 511 _et seq._

Water-falls
amount of excited activity produced at Niagara, 520
electrification produced near, 520

Watts, Marshall
atomic weight of radium, 18

Weichert
velocity of cathode rays, 76

Weight
loss of by radio-elements, 473
attempts to measure loss of in radium, 474

Wheeler and Bumstead
diffusion of radium emanation, 273
emanation from surface water and the soil, 512, 522
identity of emanation from soil with radium emanation, 512, 522

Whetham
effect of valency of ion on colloidal solutions, 215
production of radium from uranium, 463

Wiedemann
thermo-luminescence, 207

Wiedemann and Schmidt
thermo-luminescence, 207

Wien
value of _e_/_m_ for canal rays, 78
positive charge of canal rays, 78
amount of charge carried by β rays, 124

Willcock, Miss and Hardy
coloration of iodoform solution by radium rays, 214

Willemite
phosphorescence of, under radium rays, 203
use of, to show condensation of emanation, 279

Willows and Peck
action of radium rays on spark, 208

Wilson, C. T. R.
ions as nuclei of condensation, 47 _et seq._
difference between positive and negative ions as condensation nuclei,
49
equality of charges carried by positive and negative ions, 50
construction of electroscope, 86, 88
natural ionization of air in vessels, 501
radio-activity of rain and snow, 505, 506
loss of charge in closed vessels, 531 _et seq._, 534
presence of ions in dust-free air shown by condensation, 533
number of ions produced per c.c., 533
effect of pressure and nature of gas on ionization in sealed vessels,
534

Wilson, H. A.
charge on ion, 51

Wilson, W. E.
radium in sun, 491

Wölfl, Hofmann and Gonder
properties of radio-active lead, 27, 413

Wood, A.
radio-activity of ordinary materials, 540

Zara, Levi Da and Vincenti
radium emanation in spring waters, 516

Zeeman
action of magnetic field on light, 77

Zeleny
velocity of ions, 42 _et seq._
difference of velocity of ions, 45
potential gradient between electrodes, 65

Zerban and Hofmann
connection of activity of thorium with uranium, 29

Zinc Sulphide
scintillations produced in by α rays, 158
cause of luminosity of, 160, 549

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=Conduction of Electricity through Gases.= By J. J. THOMSON, D.Sc.,
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CONTENTS.

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II. Properties of a Gas when in the conducting state.

III. Mathematical Theory of the Conduction of Electricity through a
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IV. Effect produced by a Magnetic Field on the Motion of the Ions.

V. Determination of the Ratio of the Charge to the Mass of an Ion.

VI. Determination of the Charge carried by the Negative Ion.

VII. On some Physical Properties of Gaseous Ions.

VIII. Ionisation by Incandescent Solids.

IX. Ionisation in Gases from Flames.

X. Ionisation by Light. Photo-Electric Effects.

XI. Ionisation by Röntgen Rays.

XII. Becquerel Rays.

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XIV. The Electric Arc.

XV. Discharge through Gases at Low Pressures.

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XVII. Cathode Rays.

XVIII. Röntgen Rays.

XIX. Properties of Moving Electrified Bodies.

Supplementary Notes.

Index.

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