Chapter XXVII: Part VI: Alkaloids and Poisonous Vegetable Principles Separated for the (1)

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MOST PART BY ALCOHOLIC SOLVENTS.

DIVISION I.--VEGETABLE ALKALOIDS.

I.--General Methods of Testing and Extracting Alkaloids.

§ 301. =General Tests for Alkaloids.=--In order to ascertain whether an alkaloid is present or not, a method of extraction must be pursued which, while disposing of fatty matters, salts, &c., shall dissolve as little as possible of foreign substances--such a method, _e.g._, as the original process of Stas, or one of its modern modifications.

If to the acid aqueous solution finally obtained by this method a dilute solution of soda be added, drop by drop, until it is rendered feebly alkaline, _and no precipitate appear_, whatever other poisonous plant-constituents may be present, all ordinary alkaloids[324] are absent.

[324] In the case of morphine tartrate, this test will not answer. See the article on Morphine.

In addition to this negative test, there are also a number of substances which give well-marked crystalline or amorphous precipitates with alkaloids.

§ 302. These may be called “group reagents.” The chief members of the group-reagents are--Iodine dissolved in hydriodic acid, iodine dissolved in potassic iodide solution, bromine dissolved in potassic bromide solution, hydrargo-potassic iodide, bismuth-potassic iodide, cadmic potassic iodide; the chlorides of gold, of platinum, and mercury; picric acid, gallic acid, tannin, chromate of potash, bichromate of potash, phospho-molybdic acid, phospho-tungstic acid, silico-tungstic acid, and Fröhde’s reagent. It will be useful to make a few general remarks on some of these reagents.

=Iodine in hydriodic acid= gives either crystalline or amorphous precipitates with nearly all alkaloids; the compound with morphine, for example, is in very definite needles; with dilute solutions of atropine, the precipitate is in the form of minute dots, but the majority of the precipitates are amorphous, and all are more or less coloured.

=Iodine dissolved in a solution of potassic iodide= gives with alkaloids a reddish or red-brown precipitate, and this in perhaps a greater dilution than almost any reagent. When added to an aqueous solution, the precipitates are amorphous, but if added to an alcoholic solution, certain alkaloids then form crystalline precipitates; this, for example, is the case with berberine and narceine. By treating the precipitate with aqueous sulphurous acid, a sulphate of the alkaloid is formed and hydriodic acid, so that by suitable operations the alkaloid may readily be recovered from this compound. A solution of bromine in potassic bromide solution also gives similar precipitates to the above, but it forms insoluble compounds with phenol, orcin, and other substances.

=Mercuric potassic iodide= is prepared by decomposing mercuric chloride with potassic iodide in excess. The proportions are 13·546 grms. of mercuric chloride and 49·8 of potassic iodide, and water sufficient to measure, when dissolved, 1 litre. The precipitates from this reagent are white and flocculent; many of them become, on standing, crystalline.

=Bismuthic potassic iodide= in solution precipitates alkaloids, and the compounds formed are of great insolubility, but it also forms compounds with the various albuminoid bodies.

=Chloride of gold= forms with the alkaloids compounds, many of which are crystalline, and most admit of utilisation for quantitative determinations. Chloride of gold does not precipitate amides or ammonium compounds, and on this account its value is great. The precipitates are yellow, and after a while are partly decomposed, when the colour is of a reddish-brown.

=Platinic chloride= also forms precipitates with most of the alkaloids, but since it also precipitates ammonia and potassic salts, it is inferior to gold chloride in utility.

§ 303. (1.) =Phosphomolybdic Acid as a Reagent for Alkaloids.=--_Preparation_; Molybdate of ammonia is precipitated by phosphate of soda; and the well-washed yellow precipitate is suspended in water and warmed with carbonate of soda, until it is entirely dissolved. This solution is evaporated to dryness, and the ammonia fully expelled by heating. If the molybdic acid is fairly reduced by this means, it is to be moistened by nitric acid, and the heating repeated. The now dry residue is warmed with water, nitric acid added to strong acid reaction, and the mixture diluted with water, so that 10 parts of the solution contain 1 of the dry salt. The precipitates of the alkaloids are as follows:--

Aniline, Bright-yellow, flocculent.
Morphine, „ „
Narcotine, Brownish-yellow, „
Quinine, Whitish-yellow, „
Cinchonine, „ „
Codeine, Brownish-yellow, voluminous.
Strychnine, White-yellow, „
Brucine, Yelk-yellow, flocculent.
Veratrine, Bright-yellow, „
Jervine, „ „
Aconitine, „ „
Emetine, „ „
Theine, Bright-yellow, voluminous.
Theobromine, „ „
Solanine, Citron-yellow, pulverulent.
Atropine, Bright-yellow, flocculent.
Hyoscyamine, „ „
Colchicine, Orange-yellow, „
Delphinine, Grey-yellow, voluminous.
Berberine, Dirty-yellow, flocculent.
Coniine, Bright-yellow, voluminous.
Nicotine, „ „
Piperine, Brownish-yellow, flocculent.

(2.) =Silico-Tungstic Acid as a Reagent for Alkaloids.=--Sodium tungstate is boiled with freshly precipitated gelatinous silica. To the solution is added mercurous nitrate, which precipitates the yellow mercurous silico-tungstate. This is filtered, well-washed, and decomposed by an equivalent quantity of hydrochloric acid; silico-tungstic acid then goes into solution, and mercurous chloride (calomel) remains behind. The clear filtrate is evaporated to drive off the excess of hydrochloric acid, and furnishes, on spontaneous evaporation, large, shining, colourless octahedra of silico-tungstic acid, which effloresce in the air, melt at 36°, and are easily soluble in water or alcohol.

This agent produces no insoluble precipitate with any metallic salt. Cæsium and rubidium salts, even in dilute solutions, are precipitated by it; neutral solutions of ammonium chloride give with it a white precipitate, soluble with difficulty in large quantities of water. It precipitates solutions of the salts of quinine, cinchonine, morphine, atropine, &c.; if in extremely dilute solution, an opalescence only is produced: for instance, it has been observed that cinchonine hydrochlorate in 1/200000, quinia hydrochlorate in 1/20000, morphia hydrochlorate in 1/15285 dilution, all gave a distinct opalescence.--_Archiv der Pharm._, Nov., Dr. Richard Godeffroy.

(3.) =Scheibler’s Method for Alkaloids: Phospho-Tungstic Acid.=--Ordinary commercial sodium tungstate is digested with half its weight of phosphoric acid, specific gravity 1·13, and the whole allowed to stand for some days, when the acid separates in crystals. A solution of these crystals will give a distinct precipitate with the most minute quantities of alkaloids, 1/200000 of strychnine, and 1/100000 of quinine. The alkaloid is liberated by digestion with barium hydrate (or calcium hydrate); and if volatile, may be distilled off, if fixed, dissolved out by chloroform. In complex mixtures, colouring-matter may be removed by plumbic acetate, the lead thrown out by SH₂, and concentrated, so as to remove the excess of SH₂.

§ 304. =Schulze’s reagent= is phospho-antimonic acid. It is prepared by dropping a strong solution of antimony trichloride into a saturated solution of sodic phosphate. The precipitation of the alkaloids is effected by this reagent in a sulphuric acid solution.

§ 305. =Dragendorff’s reagent= is a solution of potass-bismuth iodide; it is prepared by dissolving bismuth iodide in a hot solution of potassium iodide, and then diluting with an equal volume of iodide of potassium solution. On the addition of an acid solution of an alkaloid, a kermes-red precipitate falls down, which is in many cases crystalline.

=Marm’s reagent= is a solution of potass-cadmium iodide. It is made on similar principles.

=Potass-zinc iodide= in solution is also made similarly. The precipitates produced in solutions of narceine and codeine are crystalline and very characteristic.

§ 306. =Colour Tests.=--=Fröhde’s reagent= is made by dissolving 1 part of sodic molybdate in 10 parts of strong sulphuric acid; it strikes distinctive colours with many alkaloids.

=Mandelin’s reagent= is a solution of meta-vanadate of ammonia in mono- or dihydrated sulphuric acid. The strength should be 1 part of the salt to 200 of the acid. This reagent strikes a colour with many alkaloids, and aids to their identification. It is specially useful to supplement and correct other tests. The following table gives the chief colour reactions, with the alkaloids. (See also p. 55 for the spectroscopic appearances of certain of the colour tests.)

METHODS OF SEPARATION.

§ 307. =Stas’s Process.=--The original method of Stas[325] (afterwards modified by Otto)[326] consisted in extraction of the organic matters by strong alcohol, with the addition of tartaric acid; the filtered solution was then carefully neutralised with soda, and shaken up with ether, the ethereal solution being separated by a pipette. Subsequent chemists proposed chloroform instead of ether,[327] the additional use of amyl-alcohol,[328] and the substitution of acetic, hydrochloric, and sulphuric for tartaric acid.

[325] _Annal d. Chem. u. Pharm._, 84, 379.

[326] _Ib._, 100, 44. _Anleitung zur Ausmittel. d. Gifte._

[327] Rodgers and Girwood, _Pharm. Journ. and Trans._, xvi. 497; Prollin’s _Chem. Centralb._, 1857, 231; Thomas, _Zeitschr. für analyt. Chem._, i. 517, &c.

[328] Erdmann and v. Ushlar, _Ann. Chem. Pharm._, cxx. pp. 121-360.

COLOUR REACTIONS[329] OF CERTAIN ALKALOIDS.

[329] Caustic potash also gives characteristic colours with certain alkaloids. Out of seventy-two alkaloids (using 0·5 mgrm.), the following alone gave characteristic colours when fused with KHO:--Quinine, grass-green, and peculiar odour; quinidine, becoming yellower and finally brown; cinchonine, at first brownish-red to violet, with green edges, later, bluish-green; cinchonidine, blue passing into grey; cocaine, greenish-yellow, turning to blue, and then dirty red on strong heating.--W. Lenz, _Zeit. f. anal. Chem._, 25, 29-32.

§ 308. =Selmi’s Process for Separating Alkaloids.=--A method of separating alkaloids from an ethereal solution has been proposed by Selmi.[330] The alcoholic extract of the viscera, acidified and filtered, is evaporated at 65°; the residue taken up with water, filtered, and decolorised by basic acetate of lead. The lead is thrown out by sulphuretted hydrogen; the solution, after concentration, repeatedly extracted with ether; and the ethereal solution saturated with dry CO₂, which generally precipitates some of the alkaloids. The ethereal solution is then poured into clean vessels, and mixed with about half its volume of water, through which a current of CO₂ is passed for twenty minutes; this may cause the precipitation of other alkaloids not thrown down by dry CO₂. If the whole of the alkaloids are not obtained by these means, the solution is dehydrated by agitation with barium oxide, and a solution of tartaric acid in ether is added (care being taken to avoid excess); this throws down any alkaloid still present. The detection of any yet remaining in the viscera is effected by mixing with barium hydrate and a little water, and agitating with _purified_ amylic alcohol; from the alcohol the alkaloids may be subsequently extracted by agitation with very dilute sulphuric acid.

[330] F. Selmi, _Gazett. Chim. Ital._, vj. 153-166, and _Journ. Chem. Soc._, i., 1877, 93.

Another ingenious method (also the suggestion of Selmi) is to treat the organic substance with alcohol, to which a little sulphuric acid has been added, to filter, digest with alcohol, and refilter. The filtrates are united, evaporated down to a smaller bulk, filtered, concentrated to a syrup, alkalised by barium hydrate, and, after the addition of freshly ignited barium oxide and some powdered glass, exhausted with dry ether; the ether filtered, the filtrate digested with lead hydrate; the ethereal solution filtered, evaporated to dryness, and finally again taken up with ether, which, this time, should leave on evaporation the alkaloid almost pure.

§ 309. =Dragendorff’s Process.=--To Dragendorff we owe an elaborate general method of separation, since it is applicable not only to alkaloids, but to glucosides, and other active principles derived from plants. His process is essentially a combination of those already known, and its distinctive features are the shaking up--(1) of the acid fluid with the solvent, thus removing colouring matters and certain non-alkaloidal principles; and (2) of the same fluid made alkaline. The following is his method in full. It may be advantageously used when the analyst has to search generally for vegetable poison, although it is, of course, far too elaborate for every case; and where, from any circumstance, there is good ground for suspecting the presence of one or two particular alkaloids or poisons, the process may be much shortened and modified.[331]

[331] Dragendorff’s _Gerichtlich-chemische Ermittelung von Giften_, St. Petersburg, 1876, p. 141.

I. The substance, in as finely-divided form as possible, is digested for a few hours in water acidified with sulphuric acid, at a temperature of 40° to 50°, and this operation is repeated two or three times, with filtering and pressing of the substances; later, the extracts are united. This treatment (if the temperature mentioned is not exceeded) does not decompose the majority of alkaloids or other active substances; but there are a few (_e.g._, solanine and colchicine) which would be altered by it; and, if such are suspected, maceration at the common temperature is necessary, with substitution of acetic for sulphuric acid.[332]

[332] When blood is to be examined, it is better to dry it, and then powder and extract with water acidified with dilute sulphuric acid. However, if the so-called volatile alkaloids are suspected, this modification is to be omitted.

II. The extract is next evaporated until it begins to be of a syrupy consistence; the residue mixed with three to four times its volume of alcohol, macerated for twenty-four hours at about 34°, allowed to become quite cool, and filtered from the foreign matters which have separated. The residue is washed with alcohol of 70 per cent.

III. The filtrate is freed from alcohol by distillation, the watery residue poured into a capacious flask, diluted (if necessary) with water, and filtered. Acid as it is, it is extracted at the common temperature, with frequent shaking, by freshly-rectified petroleum ether; and, after the fluids have again separated, the petroleum ether is removed, carrying with it certain impurities (colouring matter, &c.), which are in this way advantageously displaced. By this operation ethereal oils, carbolic acid, picric acid, &c., which have not been distilled, besides piperin, may also be separated. The shaking up with petroleum ether is repeated several times (as long as anything remains to be dissolved), and the products are evaporated on several watch-glasses.

RESIDUE OF PETROLEUM ETHER FROM THE ACID SOLUTION.

1. IT IS CRYSTALLINE. 2. IT IS AMORPHOUS. 3. IT IS VOLATILE,
with a powerful
odour;
_ethereal oil,
carbolic acid, &c._

A. _It is yellowish_, A. It is fixed.
and with difficulty
volatilised.

α. The crystals are α. Concentrated sul-
dissolved by concen- phuric acid dissolves
trated sulphuric it immediately--
acid, with the pro- violet, and later
duction of a clear greenish-blue.
yellow colour, pass- _Constituents of the
ing into brown and black hellebore._
greenish-brown.
_Piperin._

β. The solution in sulphuric acid β. It dissolves with a yellow
remains yellow; potassic cyanide colour, changing into fallow-
and caustic potash colour it, on brown.
warming, blood-red. _Constituents of aconite plant
_Picric acid._ and products of the decomposition
of Aconitine._

B. IT IS COLOURLESS, LIQUEFIES B. IT IS WHITE, SHARP-TASTING,
EASILY, AND SMELLS STRONGLY. AND REDDENS THE SKIN.
_Camphor and similar matters._ _Capsicin._

It may be expected that the substances mentioned under the heads 1, 2, and 3 will be, in general, fully obtained by degrees. This is not the case, however, as regards piperin and picric acid.

IV. The watery fluid is now similarly shaken up with benzene, and the benzene removed and evaporated. Should the evaporated residue show signs of an alkaloid (and especially of theine), the watery fluid is treated several times with a fresh mixture of benzene, till a little of the last-obtained benzene extraction leaves on evaporation no residue. The benzene extracts are now united, and washed by shaking with distilled water; again separated and filtered, the greater part of the benzene distilled from the filtrate, and the remainder of the fluid divided and evaporated on several watch-glasses.

The evaporated residue may contain theine, colchicine, cubebin, digitalin, cantharidin, colocynthin, elaterin, caryophylline, absinthin, cascarillin, populin, santonin, &c., and traces of veratrine, delphinine, physostigmine, and berberine.

A remnant of piperin and picric acid may remain from the previous treatment with petroleum ether.

THE BENZENE RESIDUE FROM THE ACID SOLUTION.

1. IT IS CRYSTALLINE. 2. IT IS AMORPHOUS.

A. WELL-FORMED, COLOURLESS A. COLOURLESS OR PALE YELLOW
CRYSTALS. RESIDUE.

α. Sulphuric acid dissolves the α. Sulphuric acid dissolves it at
hair-like crystals without change first yellow; the solution be-
of colour; evaporation with chlo- coming later red. Fröhde’s re-
rine water, and subsequent treat- agent does not colour it violet.
ment with ammonia, gives a _Elaterin._
murexide reaction. _Theine._

β. Sulphuric acid leaves the β. Sulphuric acid dissolves red;
rhombic crystals uncoloured. The Fröhde’s reagent violet-red;[333]
substance, taken up by oil, and tannic acid does not precipitate.
applied to the skin, produces a _Populin._
blister. _Cantharidin._

γ. Sulphuric acid leaves the γ. Sulphuric acid dissolves it
scaly crystals at first un- with a red colour; Fröhde’s
coloured, then slowly develops a reagent[334] a beautiful cherry-
reddening. It does not blister. red; tannic acid precipitates a
Warm alcoholic potash-lye colours yellowish-white. _Colocynthin._
it a transitory red. _Santonin._

δ. Sulphuric acid colours the δ. Sulphuric acid colours it
crystals almost black, whilst it gradually a beautiful red, whilst
takes itself a beautiful red tannin does not precipitate.
colour. _Cubebin._ _Constituents of the Pimento._

B. CRYSTALS PALE TO CLEAR YELLOW. B. PURE YELLOW RESIDUE.

α. _Piperin._ α. Sulphuric acid dissolves it
yellow; on the addition of nitric
acid, this solution is green,
quickly changing to blue and
violet. _Colchicine._

β. _Picric Acid._ β. Sulphuric acid dissolves with
separation of a violet powder;
caustic potash colours it red;
sulphide of ammonia violet, and,
by heating, indigo-blue.
_Chrysammic acid._

γ. Caustic potash dissolves it
purple. _Aloetin._

C. MOSTLY UNDEFINED COLOURLESS C. A GREENISH BITTER RESIDUE,
CRYSTALS. which dissolves brown in concen-
trated sulphuric acid; in
Fröhde’s reagent, likewise, at
first brown, then at the edge
green, changing into blue-violet,
and lastly violet. _Constituents
of wormwood, with absynthin,
besides quassiin, menyanthin,
ericolin, daphnin, cnicin, and
others._

α. Sulphuric acid dissolves it
green-brown; bromine colours this
solution red; dilution with water
again green. The substance
renders the heart-action of a
frog slower. _Digitalin._

β. Sulphuric acid dissolves it
orange, then brown, lastly red-
violet. Nitric acid dissolves it
yellow, and water separates as a
jelly out of the latter solution.
Sulphuric acid and bromine do not
colour it red. _Gratiolin._

γ. Sulphuric acid dissolves it
red-brown. Bromine produces in
this solution red-violet
stripes. It does not act on
frogs. _Cascarillin._

D. GENERALLY UNDEFINED YELLOW CRYSTALLISATION.--Sulphuric acid dis-
solves it olive-green. The alcoholic solution gives with potassic
iodide a colourless and green crystalline precipitate. _Berberin._

[333] Fröhde’s reagent is described at page 239.

[334] Fröhde’s reagent is described at page 239.

V. As a complete exhaustion of the watery solution is not yet attained by the benzene agency, another solvent is tried.

THE WATERY SOLUTION IS NOW EXTRACTED IN THE SAME WAY BY CHLOROFORM.

In chloroform the following substances are especially taken up:--Theobromine, narceine, papaverine, cinchonine, jervine, besides picrotoxin, syringin, digitalin, helleborin, convallamarin, saponin, senegin, smilacin. Lastly, portions of the bodies named in Process IV., which benzene failed to extract entirely, enter into solution, as well as traces of brucine, narcotine, physostigmine, veratrine, delphinine. The evaporation of the chloroform is conducted at the ordinary temperature in four or five watch-glasses.

THE CHLOROFORM RESIDUE FROM THE ACID SOLUTION.[335]

[335] Chloroform removes small portions of acetate of aconitine from acid solution, Dunstan and Umney, _J. C. S._, 1892, p. 338.

1. THE RESIDUE IS MORE OR LESS 2. THE RESIDUE IS AMORPHOUS.
MARKEDLY CRYSTALLINE.

A. _It gives in the sulphuric A. _In acetic acid solution it
acid solution evidence of an renders the action of the frog’s
alkaloid by its action towards heart slower, or produces local
iodine and iodide of potassium._ anæsthesia._

_aa_. It does not produce local
anæsthesia.

α. Sulphuric acid dissolves it α. Sulphuric acid dissolves it
without the production of colour, red-brown, bromine produces a
and chlorine and ammonia give no beautiful purple colour, water
murexide reaction. _Cinchonine._ changes it into green, hydro-
chloric acid dissolves it
greenish-brown. _Digitalin._

β. Sulphuric acid dissolves it β. Sulphuric acid dissolves it
without colour, chlorine and yellow, then brown-red; on ad-
ammonia give, as with theine, a dition of water this solution be-
murexide reaction. _Theobromine._ comes violet. Hydrochloric acid,
on warming, dissolves it red.
_Convallamarin._

_bb_. It produces local anæsthe-
sia.

α. Sulphuric acid dissolves it
brown. The solution becomes, by
extracting with water, violet,
and can even be diluted with two
volumes of water without losing
its colour. _Saponin._

β. Sulphuric acid dissolves it
yellow. On diluting with water
the same reaction occurs as in
the previous case, but more
feebly. _Senegin._

γ. Sulphuric acid does not colour γ. Sulphuric acid dissolves
in the cold; on warming, the brown, and the solution becomes
solution becomes a blue violet. red by the addition of a little
_Papaverine._ water. The action is very weak.
_Smilacin._

_cc_. Sulphuric acid dissolves it
with the production of a dirty
red, hydrochloric acid, in the
cold, with that of a reddish-
brown colour, and the last solu-
tion becomes brown on boiling.
_Constituents of the hellebore,
particularly Jervine._

δ. Sulphuric acid dissolves it in
the cold with the production of a
blue colour. _Unknown impurities,
many commercial samples of
Papaverine._

ε. Sulphuric acid dissolves it at
first grey-brown; the solution
becomes in about twenty-four
hours blood-red. Iodine water
colours it blue. _Narceine._

B. IT GIVES NO ALKALOID REACTION. B. Is inactive, and becomes blue
by sulphuric acid; by Fröhde’s
reagent[336] dark cherry-red.
Hydrochloric acid dissolves it
red. The solution becomes, by
boiling, colourless. _Syringin._

α. Sulphuric acid dissolves it
with a beautiful yellow colour;
mixed with nitre, then moistened
with sulphuric acid, and lastly
treated with concentrated soda-
lye, it is coloured a brick-red.
_Picrotoxin._

β. Sulphuric acid dissolves it
with the production of a splendid
red colour. The substance renders
the heart-action of a frog slower.
_Helleborin._

[336] Described at p. 239.

VI. THE WATERY FLUID IS NOW AGAIN SHAKEN UP WITH PETROLEUM ETHER,

in order to take up the rest of the chloroform, and the watery fluid is saturated with ammonia. The watery solution of _aconitine_ and _emetine_ is liable to undergo, through free ammonia, a partial decomposition; but, on the other hand, it is quite possible to obtain, with very small mixtures of the substances, satisfactory reactions, even out of ammoniacal solutions.

VII. THE AMMONIACAL WATERY FLUID WITH PETROLEUM ETHER.

In the earlier stages Dragendorff advises the shaking up with petroleum ether at about 40°, and the removal of the ether as quickly as possible whilst warm. This is with the intention of separating by this fluid strychnine, brucine, emetine, quinine, veratrine, &c. Finding, however, that a full extraction by petroleum ether is either difficult or not practicable, he prefers, as we have seen, to conclude the operation by other agents, coming back again upon the ether for certain special cases. Such are the volatile alkaloids; and here he recommends treatment of the fluid by _cold_ petroleum ether, taking care _not_ to hasten the removal of the latter. Strychnine and other fixed alkaloids are then only taken up in small quantities, and the greater portion remains for the later treatment of the watery fluid by benzene.

A portion of the petroleum ether, supposed to contain in solution volatile alkaloids, is evaporated in two watch-glasses; to the one, strong hydrochloric acid is added, the other being evaporated without this agent. On the evaporation of the petroleum ether, it is seen whether the first portion is crystalline or amorphous, or whether the second leaves behind a strongly-smelling fluid mass, which denotes a volatile alkaloid. If the residue in both glasses is without odour and fixed, the absence of volatile acids and the presence of fixed alkaloids, strychnine, emetine, veratrine, &c., are indicated.

THE PETROLEUM ETHER RESIDUE FROM AMMONIACAL SOLUTION.

1. IT IS FIXED AND 2. IT IS FIXED AND 3. IT IS FIXED AND
CRYSTALLINE. AMORPHOUS. ODOROUS.

A. _The crystals are A. _On adding to the
volatilised with watch-glass a little
difficulty._ hydrochloric acid,
crystals are left
behind._

_aa._ Sulphuric acid _aa._ Its solution is
dissolves it without not precipitated by
colour. platin chloride.

α. Potassic chromate α. The purest sulphuric α. The crystals of the
colours this solution acid dissolves it hydrochloric compound
a transitory blue, almost without colour; act on polarised
then red. sulphuric acid con- light; and are mostly
_Strychnine._ taining nitric acid, needle-shaped and
red quickly becoming columnar. _Coniine
orange. and Methyl-Coniine._
_Brucine._

β. Potassic chromate β. Sulphuric acid dis- β. The crystals are
does not colour it solves it yellow, cubical or tetra-
blue; with chlorine becoming deep red. hedral. _Alkaloid
water and ammonia it _Veratrine._ from Capsicum._
gives a green colour.
_Quinine._

γ. Sulphuric acid dis-
solves it brown-green;
Fröhde’s reagent red,
changing into green.
_Emetine._

_bb_. The solution of
the hydrochlorate of
the alkaloid is pre-
cipitated by platin
chloride.
_Sarracinin._

γ. Sulphuric acid B. The residue of the
dissolves it yellow, hydrochlorate of the
and the solution be- alkaloid is amor-
comes gradually a phous, or, by further
beautiful deep red. additions of HCl,
_Sabadilline._ becomes crystalline.

δ. The crystals are
easily volatilised.
_Coniine._

_aa._ Its diluted
aqueous solution is
precipitated by
platin chloride.

α. The hydrochlorate
salt, being quickly
treated with Fröhde’s
reagent, gives after
about two minutes a
violet solution which
gradually fades.
_Lobeliin._

β. The hydrochlorate
smells like nicotine,
and becomes by
Fröhde’s reagent
yellow, and after
twenty-four hours
pale red. _Nicotine._

γ. The hydrochlorate
is without odour, the
free base smells
faintly like aniline.
_Sparteine._

_bb._ The substance
is not precipitated
from a diluted solu-
tion by platin
chloride.

α. Its petroleum
ether solution pro-
duces no turbidity
with a solution of
picric acid in petro-
leum ether; but it
leaves behind, when
mixed with the above,
crystals mostly of
three-sided plates.
_Trimethylamine._

β. The petroleum
ether solution gives,
on evaporation, when
treated similarly,
moss-like crystals.
The substance is made
blue by chloride of
lime, as well as by
diluted sulphuric
acid and bichromate
of potash. _Aniline._

γ. The alkaloid does
not smell like
methylamine, and is
not coloured by chlo-
ride of lime, sul-
phuric acid, or chro-
mate of potash.
_Volatile alkaloid of
the Pimento._

VIII. THE AMMONIACAL SOLUTION IS SHAKEN UP WITH BENZENE.

In most cases petroleum ether, benzene, and chloroform are more easily separated from acid watery fluids than from ammoniacal, benzene and chloroform causing here a difficulty which has perhaps deterred many from using this method. Dragendorff, however, maintains that he has never examined a fluid in which he could not obtain a complete separation of the benzene and water. If the upper benzene layer is fully gelatinous and emulsive, the under layer of water is to be removed with a pipette as far as possible, and the benzene with a few drops of absolute alcohol and filtration. As a rule, the water goes through first alone, and by the time the greater part has run through, the jelly in the filter, by dint of stirring, has become separated from the benzene, and, finally, the jelly shrinks up to a minimum, and the clear benzene filters off. Dragendorff filters mostly into a burette, from which ultimately the benzene and the water are separated.

The principal alkaloids which are dissolved in benzene are--strychnine, methyl and ethyl strychnine, brucine, emetine, quinine, cinchonine, atropine, hyoscyamine, physostigmine, aconitine, nepalin, the alkaloid of the _Aconitum lycoctonum_, aconellin, napellin, delphinine, veratrine, sabatrin, sabadilline, codeine, thebaine, and narcotine.

THE BENZENE RESIDUE DERIVED FROM THE AMMONIACAL SOLUTION.

1. IT IS FOR THE MOST PART CRYS- 2. IT IS FOR THE MOST PART AMOR-
TALLINE. PHOUS.

_a._ Sulphuric acid dissolves it _a._ Pure sulphuric acid dis-
without colour, the solution solves it either whitish-red or
being coloured neither on stand- yellowish.
ing nor on the addition of nitric
acid.

_aa._ It dilates the pupil of a
cat.

α. Platin chloride does not pre- α. The solution becomes by nitric
cipitate the aqueous solution. acid immediately red, then quickly
The sulphuric acid solution gives, orange. _Brucine._
on warming, a peculiar smell.
_Atropine._

β. Platin chloride applied to the β. The solution becomes by little
solution precipitates. and little brownish-red. The sub-
_Hyoscyamine._ stance is coloured red by chlo-
ride of lime solution, and it
contracts the pupil.
_Physostigmine._

_bb._ It does not dilate the
pupil.

α. The sulphuric acid solution
becomes blue by chromate of
potash.

αα. The substance applied to a
frog produces tetanus.
_Strychnine._

ββ. It lowers the number of res-
pirations in a frog. _Ethyl and
Methyl Strychnine._

β. Sulphuric acid and bichromate
of potash do not colour it blue.

αα. The sulphuric acid watery so-
lution is fluorescent, and be-
comes green on the addition of
chlorine water and ammonia.
_Quinine and Cinchonine._

(The last is more difficult to
dissolve in petroleum ether than
quinine.)

ββ. The solution is not fluores-
cent. _Cinchonine._

_b._ Sulphuric acid dissolves it _b._ Pure sulphuric acid dis-
at first colourless; the solution solves it yellow, and the solu-
takes on standing a rose or tion becomes later beautiful red
violet-blue; on addition of (with delphinine, more quickly a
nitric acid, a blood-red or brown darker cherry-red.)
coloration.

α. A solution in diluted sulphuric α. The hydrochloric acid solution
acid becomes, on heating, deep gradually becomes red on heating.
blood-red, and, when cooled,
violet, with nitric acid. The
aqueous solution is precipitated
by ammonia. _Narcotine._

αα. The substance acts on a
frog, causing, in large doses,
tetanus. _Veratrine._

ββ. It is almost without action
on frogs. _Sabatrin._

β. The solution in diluted sul- β. The hydrochloric acid solution
phuric acid becomes, on heating, does not, on heating, become red.
a beautiful blue. Excess of ammo- _Delphinine._
nia does not precipitate in a
diluted watery solution.
_Codeine._

_c._ Sulphuric acid dissolves it _c._ Pure sulphuric acid dis-
with the production of a yellow solves it yellow, and the solu-
colour. tion becomes later red-brown, and
gradually violet-red.

α. The solution remains yellow α. The substance even in small
on standing. _Acolyctin._ doses paralyses frogs, and
dilates the pupil of a cat’s eye.
Ether dissolves it with diffi-
culty. _Nepalin._

β. It becomes beautifully red. β. It is easily soluble in ether,
_Sabadilline._ its effects are not so marked,
and it does not dilate the pupil.
_Aconitine._

γ. Its effects are still feeble;
it does not dilate the pupil, and
is with difficulty dissolved by
ether. _Napellin._

_d._ Sulphuric acid dissolves it _d._ Sulphuric acid dissolves it
with an immediate deep red-brown with a dark green colour, and the
colour. _Thebaine._ solution becomes, even after a
few seconds, a beautiful blood-
red. _Alkaloidal substances out
of the Aconitum lycoctonum._

_e._ Sulphuric acid dissolves it _e._ Sulphuric acid dissolves it
immediately blue. _Substances brown-green, and Fröhde’s reagent
accompanying the Papaverins._ red, becoming beautifully green.
_Emetine._

IX. SHAKING OF THE AMMONIACAL WATERY SOLUTION WITH CHLOROFORM.

This extracts the remainder of the cinchonine and papaverine, narceine, and a small portion of morphine, as well as an alkaloid from the celandine.

THE RESIDUE FROM THE CHLOROFORM.

_aa._ The solution, on warming, is only slightly coloured.

α. But, after it is again cooled, it strikes with nitric acid a
violet-blue; chloride of iron mixed with the substance gives a blue
colour; Fröhde’s reagent also dissolves it violet. _Morphine._

β. It is not coloured by nitric acid; it is also indifferent to
chloride of iron. _Cinchonine._

_bb._ The solution becomes by warming violet-blue. _Papaverine._

γ. Sulphuric acid dissolves it greenish-brown, and the solution
becomes, on standing, blood-red. _Narceine._

δ. Sulphuric acid dissolves it a violet-blue. _Alkaloidal constituent
of the Celandine._

X. SHAKING UP OF THE WATERY FLUID WITH AMYL ALCOHOL.

From this process, besides morphine and solanine, as well as salicin, the remnants of the convallamarin, saponin, senegin, and narceine are also to be expected.

THE AMYL ALCOHOL RESIDUE.

_a._ Sulphuric acid dissolves it without colour in the cold.
_Morphine_ (see above).

_b._ Sulphuric acid dissolves it with the production of a clear
yellow-red and the solution becomes brownish. Iodine water colours it
a deep brown. The alcoholic solution gelatinises. _Solanine._

_c._ Sulphuric acid dissolves it green-brown, becoming red.
_Narceine_ (see above).

_d._ Sulphuric acid dissolves it yellow, then brown-red, becoming
violet on dilution with water. Hydrochloric acid dissolves it, and it
becomes red on warming. It stops the heart-action in the systole.
_Convallamarin._

_e._ Hydrochloric acid dissolves it for the most part without colour.
_Saponin._

_f._ As the foregoing, but acting more feebly. _Senegin._

_g._ Sulphuric acid dissolves it immediately a pure red. On warming
with sulphuric acid and bichromate of potash, a smell of salicylic
acid is developed. _Salicin._

XI. DRYING THE WATERY FLUID WITH THE ADDITION OF POWDERED GLASS, AND EXTRACTION OF THE FINELY-DIVIDED RESIDUE BY CHLOROFORM.

The residue of the first chloroform extract lessens the number of respirations of a frog; the residue of the second and third chloroform extract becomes, by sulphuric acid and bichromate of potash, blue, passing into a permanent red.

Another portion of this residue becomes red on warming with diluted
sulphuric acid. _Curarine._

SHORTER PROCESS FOR SEPARATING SOME OF THE ALKALOIDS.

§ 310. A shorter process, recommended conditionally by Dragendorff, for brucine, strychnine, quinine, cinchonine, and emetine, is as follows:--

The substance, if necessary, is finely divided, and treated with sulphuric acid (dilute) until it has a marked acid reaction. To every 100 c.c. of the pulp (which has been diluted with distilled water to admit of its being filtered later), at least 5 to 10 c.c. of diluted sulphuric acid (1 : 5) are added. It is digested at 50° for a few hours, filtered, and the residue treated again with 100 c.c. of water at 50°. This extract is, after a few hours, again filtered; both the filtrates are mixed and evaporated in the water-bath to almost the consistency of a thin syrup. The fluid, however, must not be concentrated too much, or fully evaporated to dryness. The residue is now placed in a flask, and treated with three to four times its volume of alcohol of 90 to 95 per cent.; the mixture is macerated for twenty-four hours, and then filtered. The filtrate is distilled alcohol-free, or nearly so, but a small amount of alcohol remaining is not objectionable. The watery fluid is diluted to about 50 c.c., and treated with pure benzene; the mixture is shaken, and after a little time the benzene removed--an operation which is repeated. After the removal the second time of the benzene, the watery fluid is made alkaline with ammonia, warmed to 40° or 50°, and the free alkaloid extracted by twice shaking it up with two different applications of benzene. On evaporation of the latter, if the alkaloid is not left pure, it can be dissolved in acid, precipitated by ammonia, and again extracted by benzene.

§ 311. =Scheibler’s Process=.--A method very different from those
just described is one practised by Scheibler. This is to precipitate
the phosphotungstate of the alkaloid, and then to liberate the
latter by digesting the precipitate with either hydrate of barium or
hydrate of calcium, dissolving it out by chloroform, or, if
volatile, by simple distillation. The convenience of Scheibler’s
process is great, and it admits of very general application. In
complex mixtures, it will usually be found best to precede the
addition of phosphotungstic acid[337] by that of acetate of lead, in
order to remove colouring matter, &c.; the excess of lead must in
its turn be thrown out by SH₂, and the excess of SH₂ be got rid of
by evaporation. Phosphotungstic acid is a very delicate test for the
alkaloids, giving a distinct precipitate with the most minute
quantities (1/200000 of strychnine and 1/100000 of quinine). A very
similar method is practised by Sonnenschein and others with the aid
of phospho-molybdic acid. The details of Scheibler’s process are as
follows:--

[337] The method of preparing this reagent is as follows:--Ordinary commercial sodium tungstate is treated with half its weight of phosphoric acid, specific gravity, 1·13, and then allowed to stand for some days. Phosphotungstic acid separates in crystals.

The organic mixture is repeatedly extracted by water strongly
acidified with sulphuric acid; the extract is evaporated at 30° to
the consistence of a thin syrup; then diluted with water, and, after
several hours’ standing, filtered in a cool place. To the filtered
fluid phosphotungstic acid is added in excess, the precipitate
filtered, washed with water to which some phosphotungstic acid
solution has been added, and, whilst still moist, rinsed into a
flask. Caustic baryta or carbonate of potash is added to alkaline
reaction, and after the flask has been connected with bulbs
containing HCl, it is heated at first slowly, then more strongly.
Ammonia and any volatile alkaloids are driven over into the acid,
and are there fixed, and can be examined later by suitable methods.
The residue in the flask is carefully evaporated to dryness (the
excess of baryta having been precipitated by CO₂), and then
extracted by strong alcohol. On evaporation of the alcohol, the
alkaloid is generally sufficiently pure to be examined, or, if not
so, it may be obtained pure by re-solution, &c.

The author has had considerable experience of Scheibler’s process, and has used it in precipitating various animal fluids, but has generally found the precipitate bulky and difficult to manage.

§ 312. =Grandval and Lajoux’s Method=.[338]--The alkaloids are
precipitated from a solution slightly acidified by hydrochloric or
sulphuric acid by a solution of hydrarg-potassium iodide. The
precipitate is collected on a filter, washed and then transferred to
a flask; drop by drop, a solution of sodium sulphide is added; after
each addition the suspended precipitate is shaken and allowed to
stand for a few minutes, and a drop of the liquid taken out and
tested with lead acetate; directly a slight brown colour appears,
sufficient sodic sulphide has been added. The liquid is now left for
half-an-hour, with occasional shaking. Then sulphuric acid is added
until it is just acid, and the liquid is filtered and the mercury
sulphide well washed. In the filtrate will be the sulphate of any
alkaloid in solution; this liquid is now made alkaline with soda
carbonate and shaken up, as in Dragendorff’s process, with
appropriate solvents; such, for example, as ether, or chloroform, or
acetone, or amylic alcohol, according to the particular alkaloid the
analyst is searching for, and the solvent finally separated and
allowed to evaporate, when the alkaloid is found in the residue.

[338] “Dosage des alcaloides à l’aide de l’iodure double de mercure et de potassium,” par MM. A. Grandval et Henri Lajoux, _Journ. de Pharmacie_, 5 sér. t. xxviii. 152-156.

§ 313. =Identification of the Alkaloids=.--Having obtained, in one
way or other, a crystalline or amorphous substance, supposed to be
an alkaloid, or, at all events, an active vegetable principle, the
next step is to identify it. If the tests given in Dragendorff’s
process have been applied, the observer will have already gone a
good way towards the identification of the substance; but it is, of
course, dangerous to trust to one reaction.

In medico-legal researches there is seldom any considerable quantity
of the material to work upon. Hence the greatest care must be taken
from the commencement not to waste the substance in useless tests,
but to study well at the outset what--by the method of extraction
used, the microscopic appearance, the reaction to litmus paper, and
the solubility in different menstrua--it is likely to be. However
minute the quantity may be, it is essential to divide it into
different parts, in order to apply a variety of tests; but as any
attempt to do this on the solid substance will probably entail loss,
the best way is to dissolve it in a watch-glass in half a c.c. of
alcohol, ether, or other suitable solvent. Droplets of this solution
are then placed on watch-glasses or slips of microscopic glass, and
to these drops, by the aid of a glass rod, different reagents can be
applied, and the changes watched under the microscope as the drops
slowly evaporate.

§ 314. =Sublimation of the Alkaloids.=--A very beautiful and elegant aid to the identification of alkaloids, and vegetable principles generally, is their behaviour towards heat.

Alkaloids, glucosides, the organic acids, &c., when carefully heated, either--(1) sublime wholly without decomposition (like theine, cytisin, and others); or (2) partially sublime with decomposition; or (3) are changed into new bodies (as, for example, gallic acid); or (4) melt and then char; or (5) simply char and burn away.

Many of these phenomena are striking and characteristic, taking place at different temperatures, subliming in characteristic forms, or leaving characteristic residues.

One of the first to employ sublimation systematically, as a means of recognition of the alkaloids, &c., was Helwig.[339] His method was to place a small quantity (from ½ to 1/4000 of a mgrm.) in a depression on platinum foil, cover it with a slip of glass, and then carefully heat by a small flame. After Helwig, Dr. Guy[340] greatly improved the process by using porcelain discs, and more especially by the adoption of a convenient apparatus, which may be termed “the subliming cell.” It is essentially composed of a ring of glass from ⅛ to ⅔ of an inch in thickness, such as may be obtained by sections of tubing, the cut surfaces being ground perfectly smooth. This circle is converted into a closed cell by resting it on one of the ordinary thin discs of glass used as a covering for microscopic purposes, and supporting a similar disc. The cell was placed on a brass plate, provided with a nipple, which carried a thermometer, and was heated by a small flame applied midway between the thermometer and the cell; the heat was raised very gradually, and the temperature at which any change took place was noted. In this way Dr. Guy made determinations of the subliming points of a large number of substances, and the microscopic appearances of the sublimates were described with the greatest fidelity and accuracy. On repeating with care Dr. Guy’s determinations, however, I could in no single instance agree with his subliming points, nor with the apparatus he figures and describes could two consecutive observations exactly coincide. Further, on examining the various subliming temperatures of substances, as stated by different authors, the widest discrepancies were found--differences of 2 or even 3 degrees might be referred to errors of observation, a want of exact coincidence in the thermometers employed, and the like; but to what, for example, can we ascribe the irreconcilable statements which have been made with regard to theine? According to Strauch, this substance sublimes at 177°; according to Mulder, at 184·7°. But that both of these observations deviate more than 70° from the truth may be proved by any one who cares to place a few mgrms. of theine, enclosed between two watch-glasses, over the water-bath; in a few minutes a distinct sublimate will condense on the upper glass, and, in point of fact, theine will be found to sublime several degrees below 100°.

[339] _Das Mikroskop in der Toxicologie_.

[340] _Pharm. Journ. Trans_. (2), viij. 719; ix. 10, 58. _Forensic Medicine_, London, 1875.

Since this great divergency of opinion is not found either in the specific gravity, or the boiling-points, or any of the like determinations of the physical properties of a substance, it is self-evident that the processes hitherto used for the determination of subliming points are faulty. The sources of error are chiefly--

(1.) Defects in the apparatus employed--the temperature read being rather that of the metallic surface in the immediate vicinity of the thermometer than of the substance itself.

(2.) The want of agreement among observers as to what should be called a sublimate--one considering a sublimate only that which is evident to the naked eye, another taking cognisance of the earliest microscopic film.

(3.) No two persons employing the same process.

With regard to the apparatus employed, I adopt Dr. Guy’s subliming cell; but the cell, instead of resting on a metallic solid, floats on a metallic fluid. For any temperature a little above 100° this fluid is mercury, but for higher temperatures fusible metal is preferable.

The exact procedure is as follows:--A porcelain crucible (_a_ in fig.), about 3 inches in diameter, is nearly filled with mercury or fusible metal, as the case may be; a minute speck (or two or three crystals of the substance to be examined) is placed on a thin disc of microscopic covering glass, floated on the liquid, and the cell is completed by the glass ring and upper disc. The porcelain crucible is supported on a brass plate (_b_), fixed to a retort-stand in the usual way, and protected from the unequal cooling effects of currents of air by being covered by a flask (_c_), from which the bottom has been removed. The neck of the flask conveniently supports a thermometer, which passes through a cork, and the bulb of the thermometer is immersed in the bath of liquid metal. In the first examination of a substance the temperature is raised somewhat rapidly, taking off the upper disc with a forceps at every 10° and exchanging it for a fresh disc, until the substance is destroyed. The second examination is conducted much more slowly, and the discs exchanged at every 4° or 5°, whilst the final determination is effected by raising the temperature with great caution, and exchanging the discs at about the points of change (already partially determined) at every half degree. All the discs are examined microscopically. The most convenient definition of a sublimate is this--the most minute films, dots, or crystals, which can be observed by ¼-inch power, and which are obtained by keeping the subliming cell at a definite temperature for 60 seconds. The commencement of many sublimates assumes the shape of dots of extraordinary minuteness, quite invisible to the unaided eye; and, on the other hand, since the practical value of sublimation is mainly as an aid to other methods for the recognition of substances, if we go beyond _short_ intervals of time, the operation, otherwise simple and speedy, becomes cumbersome, and loses its general applicability.

There is also considerable discrepancy of statement with regard to the melting-point of alkaloidal bodies; in many instances a viscous state intervenes before the final complete resolution into fluid, and one observer will consider the viscous state, the other complete fluidity, as the melting-point.

In the melting-points given below, the same apparatus was used, but the substance was simply placed on a thin disc of glass floating on the metallic bath before described (the cell not being completed), and examined from time to time microscopically, for by this means alone can the first drops formed by the most minute and closely-adherent crystals to the glass be discovered.

=Cocaine= melts at 93°, and gives a faint sublimate at 98°; if put between two watch-glasses on the water-bath, in fifteen minutes there is a good cloud on the upper glass.

=Aconitine= turns brown, and melts at 179° C.; it gives no characteristic sublimate up to 190°.

=Morphine=, at 150°, clouds the upper disc with nebulæ; the nebulæ are resolved by high magnifying powers into minute dots; these dots gradually become coarser, and are generally converted into crystals at 188°; the alkaloid browns at or about 200°.

=Thebaine= sublimes in theine-like crystals at 135°; at higher temperatures (160° to 200°), needles, cubes, and prisms are observed. The residue on the lower disc, if examined before carbonisation, is fawn-coloured with non-characteristic spots.

=Narcotine= gives no sublimate; it melts at 155° into a yellow liquid, which, on raising the temperature, ever becomes browner to final blackness. On examining the residue before carbonisation, it is a rich brown amorphous substance; but if narcotine be heated two or three degrees above its melting-point, and then cooled slowly, the residue is crystalline--long, fine needles radiating from centres being common.

=Narceine= gives no sublimate; it melts at 134° into a colourless liquid, which undergoes at higher temperatures the usual transition of brown colours. The substance, heated a few degrees above its melting-point, and then allowed to cool slowly, shows a straw-coloured residue, divided into lobes or drops containing feathery crystals.

=Papaverine= gives no sublimate; it melts at 130°. The residue, heated a little above its melting-point, and then slowly cooled, is amorphous, of a light-brown colour, and in no way characteristic.

=Hyoscyamine= gives no crystalline sublimate; it melts at 89°, and appears to volatilise in great part without decomposition. It melts into an almost colourless fluid, which, when solid, may exhibit a network not unlike vegetable parenchyma; on moistening the network with water, interlacing crystals immediately appear. If, however, hyoscyamine be kept at 94° to 95° for a few minutes, and then slowly cooled, the edges of the spots are arborescent, and the spots themselves crystalline.

=Atropine= (daturine) melts at 97°; at 123° a faint mist appears on the upper disc. Crystals cannot be obtained; the residue is not characteristic.

=Solanine.=--The upper disc is dimmed with nebulæ at 190°, which are coarser and more distinct at higher temperatures; at 200° it begins to brown, and then melts; the residue consists of amber-brown, non-characteristic drops.

=Strychnine= gives a minute sublimate of fine needles, often disposed in lines, at 169°; about 221° it melts, the residue (at that temperature) is resinous.

=Brucine= melts at 151° into a pale yellow liquid, at higher temperatures becoming deep-brown. If the lower disc, after melting, be examined, no crystals are observed, the residue being quite transparent, with branching lines like the twigs of a leafless tree; light mists, produced rather by decomposition than by true sublimation, condense on the upper disc at 185°, and above.

=Saponin= neither melts nor sublimes; it begins to brown about 145°, is almost black at 185°, and quite so at 190°.

=Delphinine= begins to brown about 102°; it becomes amber at 119°, and melts, and bubbles appear. There is no crystalline sublimate; residue not characteristic.

=Pilocarpine= gives a distinct crystalline sublimate at 153°; but thin mists, consisting of fine dots, may be observed as low as 140°. Pilocarpine melts at 159°; the sublimates at 160° to 170° are in light yellow drops. If these drops are treated with water, and the water evaporated, feathery crystals are obtained; the residue is resinous.

=Theine= wholly sublimes; the first sublimate is minute dots, at 79°; at half a degree above that very small crystals may be obtained; and at such a temperature as 120°, the crystals are often long and silky.

=Theobromine= likewise wholly sublimes; nebulæ at 134°, crystals at 170°, and above.

=Salicin= melts at 170°; it gives no crystalline sublimate. The melted mass remains up to 180° almost perfectly colourless; above that temperature browning is evident. The residue is not characteristic.

=Picrotoxin= gives no crystalline sublimate. The lowest temperature at which it sublimes is 128°; the usual nebulæ then make their appearance; between 165° and 170° there is slight browning; at 170° it melts. The residue, slowly cooled, is not characteristic.

=Cantharidin= sublimes very scantily between 82° and 83°; at 85° the sublimate is copious.

The active principles of plants may, in regard to their behaviour to heat, be classed for practical purposes into--

1. Those which give a decided crystalline sublimate:
(_a._) Below 100°, _e.g._, cocaine, theine, thebaine, cantharidin.
(_b._) Between 100° and 150°, _e.g._, quinetum.
(_c._) Between 150° and 200°, _e.g._, strychnine, morphine,
pilocarpine.
2. Those which melt, but give no crystalline sublimate:
(_a._) Below 100°, _e.g._, hyoscyamine, atropine.
(_b._) Between 100° and 150°, _e.g._, papaverine.
(_c._) Between 150° and 200°, _e.g._, salicin.
(_d._) Above 200°, _e.g._, solanine.
3. Those which neither melt nor give a crystalline sublimate, _e.g._,
saponin.

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Poisons, Their Effects and DetectionChapter XXVII: Part VI: Alkaloids and Poisonous Vegetable Principles Separated for the (1)

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