Chapter C: W. HEATON, F.I.C., F.C.S., Lecturer on Chemistry at the (18)

-------+--------+-------+--------+-------+--------+-------+--------+-------+--------
Degrees|Specific|Degrees|Specific|Degrees|Specific|Degrees|Specific|Degrees|Specific
Baumé. |Gravity.|Baumé. |Gravity.|Baumé. |Gravity.|Baumé. |Gravity.|Baumé. |Gravity.
-------+--------+-------+--------+-------+--------+-------+--------+-------+--------
10 | 1·0000 | 21 | 0·9300 | 32 | 0·8690 | 42 | 0·8202 | 52 | 0·7766
11 | 0·9932 | 22 | 0·9241 | 33 | 0·8639 | 43 | 0·8156 | 53 | 0·7725
12 | 0·9865 | 23 | 0·9183 | 34 | 0·8588 | 44 | 0·8111 | 54 | 0·7684
13 | 0·9799 | 24 | 0·9125 | 35 | 0·8538 | 45 | 0·8066 | 55 | 0·7643
14 | 0·9733 | 25 | 0·9068 | 36 | 0·8488 | 46 | 0·8022 | 56 | 0·7604
15 | 0·9669 | 26 | 0·9012 | 37 | 0·8439 | 47 | 0·7978 | 57 | 0·7556
16 | 0·9605 | 27 | 0·8957 | 38 | 0·8391 | 48 | 0·7935 | 58 | 0·7526
17 | 0·9542 | 28 | 0·8902 | 39 | 0·8343 | 49 | 0·7892 | 59 | 0·7487
18 | 0·9480 | 29 | 0·8848 | 40 | 0·8295 | 50 | 0·7849 | 60 | 0·7449
19 | 0·9420 | 30 | 0·8795 | 41 | 0·8249 | 51 | 0·7807 | 61 | 0·7411
20 | 0·9359 | 31 | 0·8742 | | | | | |
-------+--------+-------+--------+-------+--------+-------+--------+-------+---------

[Footnote 77: These instruments were originally adjusted at the temperature of 12-1/2° Cent., or 54-1/2° Fahr. Those now made in France are adjusted at 15° C., or 59° F.; and those made in England, at either 59° or (more usually) 60° Fahr. The standard temperature of the instrument must be known for its correct application.]

2. _Areometer for liquids_ HEAVIER _than_ WATER;
_Pèse-acide_, or _Pèse-sirop_.[78]

+-------+--------+-------+--------+-------+--------+-------+--------+-------+--------+
|Degrees|Specific|Degrees|Specific|Degrees|Specific|Degrees|Specific|Degrees|Specific|
|Baumé. |Gravity.|Baumé. |Gravity.|Baumé. |Gravity.|Baumé. |Gravity.|Baumé. |Gravity.|
+-------+--------+-------+--------+-------+--------+-------+--------+-------+--------+
| 0 | 1·0000 | 16 | 1·1176 | 32 | 1·2667 | 47 | 1·4476 | 62 | 1·6889 |
| 1 | 1·0066 | 17 | 1·1259 | 33 | 1·2773 | 48 | 1·4615 | 63 | 1·7079 |
| 2 | 1·0133 | 18 | 1·1343 | 34 | 1·2881 | 49 | 1·4758 | 64 | 1·7273 |
| 3 | 1·0201 | 19 | 1·1428 | 35 | 1·2992 | 50 | 1·4902 | 65 | 1·7471 |
| 4 | 1·0270 | 20 | 1·1515 | 36 | 1·3103 | 51 | 1·5051 | 66 | 1·7674 |
| 5 | 1·0340 | 21 | 1·1603 | 37 | 1·3217 | 52 | 1·5200 | 67 | 1·7882 |
| 6 | 1·0411 | 22 | 1·1692 | 38 | 1·3333 | 53 | 1·5353 | 68 | 1·8095 |
| 7 | 1·0483 | 23 | 1·1783 | 39 | 1·3451 | 54 | 1·5510 | 69 | 1·8313 |
| 8 | 1·0556 | 24 | 1·1875 | 40 | 1·3571 | 55 | 1·5671 | 70 | 1·8537 |
| 9 | 1·0630 | 25 | 1·1968 | 41 | 1·3694 | 56 | 1·5833 | 71 | 1·8765 |
| 10 | 1·0704 | 26 | 1·2063 | 42 | 1·3818 | 57 | 1·6000 | 72 | 1·9000 |
| 11 | 1·0780 | 27 | 1·2160 | 43 | 1·3945 | 58 | 1·6170 | 73 | 1·9241 |
| 12 | 1·0857 | 28 | 1·2258 | 44 | 1·4074 | 59 | 1·6344 | 74 | 1·9487 |
| 13 | 1·0935 | 29 | 1·2358 | 45 | 1·4206 | 60 | 1·6522 | 75 | 1·9740 |
| 14 | 1·1014 | 30 | 1·2459 | 46 | 1·4339 | 61 | 1·6705 | 76 | 2·0000 |
| 15 | 1·1095 | 31 | 1·2562 | | | | | | |
+-------+--------+-------+--------+-------+--------+-------+--------+-------+--------+

II.--_Corresponding_ SPECIFIC GRAVITIES _and_ DEGREES _of_ BAUMÉ'S AREOMETER _for heavy liquids_.[78] From the Batavian Pharmacop[oe]ia.

[Footnote 78: See footnote on previous page.]

+-------+--------+-------+--------+-------+--------+-------+--------+-------+--------+
|Degrees|Specific|Degrees|Specific|Degrees|Specific|Degrees|Specific|Degrees|Specific|
|Baumé. |Gravity.|Baumé. |Gravity.|Baumé. |Gravity.|Baumé. |Gravity.|Baumé. |Gravity.|
+-------+--------+-------+--------+-------+--------+-------+--------+-------+--------+
| 0 | 1000 | 16 | 1125 | 32 | 1286 | 47 | 1485 | 62 | 1758 |
| 1 | 1007 | 17 | 1134 | 33 | 1298 | 48 | 1501 | 63 | 1779 |
| 2 | 1014 | 18 | 1143 | 34 | 1309 | 49 | 1516 | 64 | 1801 |
| 3 | 1022 | 19 | 1152 | 35 | 1321 | 50 | 1532 | 65 | 1823 |
| 4 | 1029 | 20 | 1161 | 36 | 1334 | 51 | 1549 | 66 | 1847 |
| 5 | 1036 | 21 | 1171 | 37 | 1346 | 52 | 1566 | 67 | 1872 |
| 6 | 1044 | 22 | 1180 | 38 | 1359 | 53 | 1583 | 68 | 1897 |
| 7 | 1052 | 23 | 1190 | 39 | 1372 | 54 | 1601 | 69 | 1921 |
| 8 | 1060 | 24 | 1199 | 40 | 1384 | 55 | 1618 | 70 | 1946 |
| 9 | 1067 | 25 | 1210 | 41 | 1398 | 56 | 1637 | 71 | 1974 |
| 10 | 1075 | 26 | 1221 | 42 | 1412 | 57 | 1656 | 72 | 2000 |
| 11 | 1083 | 27 | 1231 | 43 | 1426 | 58 | 1676 | 73 | 2031 |
| 12 | 1091 | 28 | 1242 | 44 | 1440 | 59 | 1695 | 74 | 2059 |
| 13 | 1100 | 29 | 1252 | 45 | 1454 | 60 | 1715 | 75 | 2087 |
| 14 | 1108 | 30 | 1261 | 46 | 1470 | 61 | 1738 | 76 | 2116 |
| 15 | 1116 | 31 | 1275 | | | | | | |
+-------+--------+-------+--------+-------+--------+-------+--------+-------+--------+

=AREOM'ETRY.= _Syn._ AREOME'TRIA, L.; ARÉOMÉTRIE, Fr. The art or operation of ascertaining the specific gravity of liquids, and hence also their strength or commercial value; hydrometry. See AREOMETER (_above_), HYDROMETRY, SPECIFIC GRAVITY, &c.

=ARE'CINA.= C_{23}H_{26}N_{2}O_{4}. An alkaloid discovered by Pelletier and Comol, in white cinchona bark from Aréca. It is extracted from the bark by the same process as Quinine, viz., by boiling the bark with acidulated water, treating the liquor with lime, and digesting the lime-precipitate in alcohol. The solution filtered at the boiling heat yields a very dark-coloured liquid, which, after a time, deposits the greater part of the aricine in crystals. An additional quantity may be obtained from the mother-liquor by expelling the alcohol by distillation, treating the residue with a slight excess of hydrochloric acid, separating the greater part of the colouring matter by means of a saturated solution of common salts, then throwing down the aricine by ammonia, dissolving the precipitate in alcohol, decolourising with animal charcoal and crystallising.

=ARGAMONE MEXICANA= (nat. order PAPAVERACEÆ). A tropical American plant, now a common weed growing in almost every part of India. A fixed oil is obtained from the seeds by expression, which has long been employed as an aperient in the West Indies. In half-drachm doses it is said to act as a gentle aperient, and at the same time it allays, apparently by its sedative qualities, the pain in colic. The smallness of the dose, and the mildness of its operation, commend it to the notice of the medical practitioner. Its efficiency is impaired by keeping, the freshly prepared oil proving more active and uniform in its action than that which has been long on hand. It is reported to exercise a well-marked and soothing influence when applied to herpetic eruptions and other forms of skin disease. By the natives of India the expressed yellow glutinous juice of the plant is held in high repute as a local application to indolent and foul ulcers.

=ARGENT'INE= (-[)i]n). _Syn._ ARGENTI'NUS, L.; ARGENTIN, Fr.; SILBERFARBEN, &c., Ger. Silver-like; pertaining to, resembling, or sounding like silver; argental.

=Ar'gentine.= (-t[)i]n). [Eng., Fr.] German silver*. In _mineralogy_, nacreous carbonate of lime, from its whiteness and silvery lustre.

=ARGENT'UM.= [L.] Silver. In _old chemistry_ and _pharmacy_, ARGENTUM, FUGITI''VUM[dagger], A. MO'BILE[dagger] (-[)i]l-e), was quicksilver; A. MOR'TUUM[dagger], dead silver, grain-s; A. MUSI'VUM[dagger], mosaic s., silver-bronze; A. NITRA'TUM[dagger], lunar caustic; A. VI'VUM[dagger], quicksilver; A. ZOÖTIN'ICUM[dagger], cyanide of silver; &c.

=AR'GIL=[dagger] (j[)i]l). _Syn._ ARGIL'LA, L.; ARGILE, Fr. Clay or potter's earth.

=ARGILLA'CEOUS= (-j[)i]l-). _Syn._ ARGILLA'CEUS, L.; ARGILLEUX, Fr.; THONIG, THONARTIG, Ger. Clayey; pertaining to, containing, or of the nature of clay or argil. In _agriculture_, an epithet of soils (ARGILLACEOUS SOILS) of which clay is the principal or characteristic ingredient.

=Argil'lo-arena'ceous= (-j[)i]l-). In _agr._, consisting chiefly of clay and sand.

=Argillo-calca''reous.= In _agr._, consisting chiefly of clay and chalk.

=AR'GOL.= _Syn._ ARGAL*; TAR'TARUS CRU'DUS, L.; TARTRE BRUT, Fr.; WEINSTEIN, Ger. Crude bitartrate of potash, as deposited by wine. That from red wine is RED ARGOL; that from white wine, WHITE ARGOL. See TARTAR.

=ARM'ATURE= (-[)a]-t[=u]re). _Syn._ ARMATU''RA, L. In _magnetism_, a piece of soft iron used to connect the poles of a horseshoe magnet, for the purpose of preventing loss of power.

=AR'NICA.= [L., Fr., Eng.] _Syn._ ARNIQUE, Fr.; ARNIKA, WOLVERLEI, Ger. In _botany_, a genus of plants of the nat. ord. Compositæ (DC.). In the Ph. U. S., arnica montana (see _below_).

=Arnica Monta'na.= [L.; Linn.] _Syn._ ARNICA, MOUN'TAIN A., M. TOBAC'CO, GERMAN LEOP'ARD'S BANE; PANACE'A LAPSO''RUM*, L. ARNIQUE, A. DES MONTAGNES, TABAC DES SAVOYARDS ET DES VOSGES, Fr.; ARNIKA, FALKRAUT, &c., Ger. _Hab._ Meadows of the cooler parts of Europe, North America, and Siberia. It is now cultivated in our gardens. Flowers (ARNICA, Ph. U. S., Castr. Ruth., and Bor.) and leaves, diaphoretic, diuretic, stimulant, and narcotic; in large doses emetic and purgative; root discutient; whole herb diaphoretic, stimulant, and nervine.

_Prop., &c._ Arnica acts as an energetic stimulant on the cerebro-spinal system, and as an irritant on the stomach and bowels. It is much employed on the Continent, and is given in a great variety of diseases--amaurosis, chlorosis, convulsions, diarrh[oe]a, dysentery, gout, paralysis, rheumatism, &c. It is much used in Germany, instead of bark, in intermittents, putrid fevers, and gangrene. In France it is commonly employed as an excito-tonic in paralysis. It has been greatly extolled, as a restorative, and in bruises and injuries from falls. The Savoyards and inhabitants of the Vosges both smoke and 'snuff' the leaves. In England it is little used except by hom[oe]opaths. It is said that no animal but the goat will eat this plant. (Thomson.) Its noxious properties chiefly depend on the presence of cytisine.--_Dose._ Flowers, 5 to 10 gr., in powder, with syrup or honey; root, 10 to 20 gr. It is most conveniently administered under the form of infusion or tincture. Severe abdominal pains and vertigo, and even tetanus and death, have followed excessive doses.

_Obs._ According to Dupuytren, the emetic action of infusion of arnica depends on minute particles of the down of the plant which remain suspended in it, and which may be removed by filtration. See INFUSIONS, TINCTURES, &c.

=ARNATT'O, Arnott'o.= See ANNOTTA.

=AR'NICINE= (seen). This name has been applied to two substances--the one discovered by Pfaff; the other by Bastick:--

=Arnicine= (of Pfaff). The resinous matter extracted by alcohol from the roots and flowers of mountain arnica, and in which their acridity appears to reside.

=Arnicine= (of Bastick). _Syn._ ARNICI'NA, ARNICI''A (n[=i]sh'-y'[)a]), L. _Prep._ 1. (Bastick.) From the flowers, by a similar process to that by which he obtains lobelina. 2. From the flowers (or root), as directed under ARICINA.

_Prop., &c._ Bitter; acrid; crystallisable scarcely soluble in water; soluble in alcohol and ether; forms salts with the acids, the hydrochlorate and one or two others being crystallisable. Its physiological properties and dose have not as yet been accurately determined.

=ARO'MA.= [L.] _Syn._ AROME, Fr.; AROM, GERUCHSTOFF, Ger. The characteristic odour of substances, particularly the peculiar quality of plants, and of substances derived from them, which constitutes their fragrance.

=AROMA'TA.= [L.] See AROMATIC.

=AROMAT'IC.= _Syn._ AROMAT'ICUS, L.; AROMATIQUE, Fr.; GEWÜRZHAFT, Ger. Fragrant; odoriferous; spicy; applied chiefly to plants and their products (AROMATICS, A. PLANTS; AROMAT'A, AROMAT'ICA, L.; AROMATIQUES, ÉPICES, Fr.; GEWURZ, Ger.) characterised by their spicy odour or aroma, and warm pungent flavour, and of which allspice, cinnamon, cloves, lavender, pepper, rosemary, sage, &c., are well-known examples. They are all stimulant, carminative, and antiseptic; and from remote antiquity have been regarded as prophylactic and disinfectant.

=Aromatic.= In _medicine_, _pharmacy_, _perfumery_, &c., applied to substances, simple or compound, characterised by an agreeable odour or carminative properties, or both; as aromatic confection, a. pastilles, a. vinegar, a. bark (CORTEX AROMATICUS, white canella), &c.

=AROMATIC SULPHUR-SOAP= (Ed. Heger). For cleansing the teeth and mouth. A hard sulphur-coloured soap externally; on cutting, greyish-brown. Composed of soap with 10 per cent. of hyposulphite of soda, perfumed with a scent resembling oil of balm. (Hager.)

=AROMATIQUE= (Albin Müller, Brünn). Spirit (90 per cent.), 50 grms.; sugar, 45 grms.; extractive matter, 4 grms. (composed of cinnamon, cloves, galangal, zedoary, angelica, anise); water, 81 grms. Sold in wine-bottle-shaped bottles, and recommended for all derangements of the digestive organs. (Hager.)

=ARQUEBUSADE'= (ar-ke-b[)o][)o]-zade'). [Fr.] Primarily, the shot of an arquebuse; but afterwards applied to an aromatic spirit (EAU D'ARQUEBUSADE, Fr.), originally employed as an application to gunshot (arquebuse) wounds.

=AR'RACK= (_Syn._ RACK) (arrack'--Brande). [Ind.] _Syn._ ARAC, ARACK, RACK[double-dagger]§; PALM-SPIRIT; AR'AC'CA, SPIR'ITUS PAL'MÆ, S. SUC'CI P., S. ORY'ZÆ*, L.; ARACK, Fr.; Arak, Ger. A spirituous liquor imported from the East Indies. The finer qualities are distilled from the fermented juice (toddy, palm-wine) of the cocoa-nut tree, palmyra tree, and other palms; and the other kinds, from the infusion of unhusked rice (rice-beer), fermented with cocoa-nut or palm-juice, either with or without the addition of coarse sugar or jaggery.

_Prop., &c._ It is colourless or nearly so, but like other spirit, when long kept in wood, gradually acquires a slight tinge, similar to that of old Hollands. The best kinds, when of sufficient age, are pleasant flavoured, and are probably as wholesome as the other spirits of commerce; but common arrack has a strong and somewhat nauseous flavour and odour, depending on the presence of volatile oil derived from the rice, and corresponding to that of corn-spirit. The inferior qualities are hence more heating and apt to disagree with the stomach than the other commercial spirits. In this country it is chiefly used to make punch. When sliced pine-apples are put into good arrack, and the spirit kept for some time, it mellows down and acquires a most delicious flavour, and is thought by many to be then unrivalled for making 'nectarial punch' or 'rack-punch.'

_Obs._ Batavian arrack is most esteemed; then that of Madras; and next that of China. Others are regarded as inferior. The common par'iah arrack is generally narcotic, very intoxicating, and unwholesome; being commonly prepared from coarse jaggery, spoilt toddy, refuse rice, &c., and rendered more intoxicating by the addition of hemp-leaves, poppy-heads, juice of stramonium, and other deleterious substances.

=Arrack, Facti''tious.= _Syn._ MOCK AR'RACK, BRIT'ISH A.; VAUXHALL'NEC'TAR; &c. _Prep._ Good old Jamaica rum (uncoloured), rectified spirit (54 to 56 o. p.; clean flavoured), and water, of each 1 quart; flowers of benzoin, 1 dr.; sliced pine-apple, 1/4 oz. (or essence of pine-apple, 1/2 teaspoonful); digest, with occasional agitation, for a fortnight; then add of skimmed milk 1 wine-glassful; agitate well for 15 minutes, and in a few days decant the clear portion.

The crude Indian arrack, when subjected to distillation until it has a sp. gr. ·920, is employed in India, as proof spirit, in the preparation of official tinctures, and for other pharmaceutical purposes. A very useful stimulating application, known in India as toddy poultice, and intended as a substitute for yeast poultice, is prepared by adding freshly drawn toddy to rice flour, till it has the consistence of a soft poultice, and subjecting this to heat over a gentle fire, stirring constantly till fermentation commences.

The light brown cotton-like substance from the outside of the base of the fronds belonging to the Palmyra palm is employed by the Cyngalese doctors as a styptic for stopping the hæmorrhage of superficial wounds.

=AR'ROW-ROOT.= The common name of _maran'ta arundina'cea_ (Linn.; _m. Indi'ca_--Tuss.); a plant of the nat. ord. Marantaceæ (Lindl.; Cannaceæ--Endl.). It was originally brought from the island of Dominica to Barbadoes, by Col. James Walker. It has since been extensively cultivated in the West Indies.

_Tubers_ yield true ARROW-ROOT; when fresh and good they contain about 26% of starch, of which 23% may be obtained as arrow-root, and the rest by boiling.

=Arrow-root.= _Syn._ MARAN'TA, AM'YLUM MARAN'TÆ, FÆC'ULA M., L.; RACINE FLÉCHIÈRE, PIVOT, Fr.; PFEILWURZ, P.-SATZMEHL, Ger. The starch or fecula obtained from the rhizoma or tubers of _maran'ta arundina'cea_ (Linn.; see _above_), and which forms the true 'arrow-root' of commerce.

_Prep._ The fecula is extracted from the tubers when they are about 10 or 12 months old, by a process similar to that by which the farina is obtained from potatoes. In Bermuda the tubers, after being washed, are deprived of their paper-like scales and every discoloured and defective part by hand; they are then again washed and drained, and next subjected to the action of a wheel-rasp, the starch being washed from the comminuted tubers with rain-water; the milky liquid is passed through a hair sieve, or a coarse cloth, and allowed to deposit its fecula. This is then allowed to drain, after which it is again carefully washed with clean water, again drained, and, after being thoroughly dried in the air or sun, is at once packed for market. (Cogswell.) In St. Vincent (on the Hopewell Estate), a cylindrical crushing-mill, tinned-copper washing machines, and German-silver palettes and shovels are employed; whilst the drying is effected in extensive sheds, under white gauze, to exclude insects. In Jamaica the washed tubers are generally pulped in deep wooden mortars; machinery being seldom employed in any part of the process.

_Prop., &c._ A light, dull, dead-white, tasteless, inodorous powder or small pulverulent masses, feeling firm to the fingers, and crackling when pressed or rubbed; viewed by a pocket lens it appears to consist of glistening particles, which are shown by a microscope to be convex, irregular, ovoid or truncated granules, most of them, according to Mr Jackson, being ·0010 of an inch in length, and ·0008 of an inch in breadth; mixed with others varying from about double to only half that size. In its action with boiling water, and its general properties it resembles the other starches; than which, however, it is freer from any peculiar taste and flavour; and thus agrees better with the delicate stomachs of invalids and infants than the ordinary farinas.

_Comp._ Similar to that of the other starches.

_Pur._ A large portion of the arrow-root of the shops consists either wholly or in part of the fecula or farina of potatoes or of inferior starches such as _cacuma_, or East Indian arrow-root, _jatropha_, or Brazilian arrow-root, _canna_, or _tous les mois_; or is more or less mixed with sago-meal or rice-meal: such materials can be readily detected by the microscope. Potato starch is known in commerce as 'FARINA' or 'BRITISH ARROW-ROOT,' or simply 'arrow-root,' whereas genuine arrow-root is always described as 'Bermuda,' 'St. Vincent,' 'St. Kitts,' or, at least, as 'West Indian arrow-root.' The substitution of the inferior farinas for genuine arrow-root is not only fraudulent on account of their inferior value, but is reprehensible in a hygienic point of view; as some of them are offensive to a delicate stomach, and exert of themselves, and still more when carelessly manufactured, a laxative action on the bowels; whereas the effect of true arrow-root is that of a slight and soothing tonic.

_Uses, &c._ As an agreeable, non-irritable article of diet for invalids and children, in the form of cakes, biscuits or puddings, or boiled with milk or water and flavoured with sugar, spices, lemon-juice, or wine, at pleasure. For young children a little caraway or cinnamon water is to be preferred. It is especially useful in irritation or debility of the stomach, bowels, or urinary organs, and in all cases in which a demulcent or emollient is indicated. It must not, however, be employed to the entire exclusion of other food, as, being destitute of the nitrogenous elements of nutrition, it is incapable alone of supporting life. Arrow-root jelly is prepared by first rubbing the powder up with a very small quantity of cold water, and then gradually adding the remainder boiling, stirring well all the time. Beef tea, veal broth, or milk may be used instead of water. Some persons boil it for a few minutes. This jelly, flavoured with a little genuine port wine and nutmeg, is almost a specific in cases of simple diarrh[oe]a arising from habit or debility.

_Obs._ Arrow-root is imported in tins, barrels, and boxes, from all the West India Islands; and from Calcutta and Sierra Leone. The best quality was, until recently, solely obtained from Bermuda; but of late equally fine samples have been produced on the Hopewell Estate, St Vincent, and, according to Dr Ure, with the advantage of being prepared with the purest spring water, in profusion, instead of rain water.

In _commerce_, the word arrow-root is now often loosely used as a generic term to indicate any white, tasteless, and edible starch or fecula.

=Arrow-root, Brazil'ian.= Cassava-starch or tapioca-meal.

=Arrow-root, East In'dian.= Curcuma starch; from the tubers of the _curcuma angustifolia_ or narrow-leaved turmeric. The _maranta arundinacea_ is now also extensively cultivated in India under the name of maranta Indica, and the fecula therefrom extensively exported, which might, with equal propriety, be called East Indian arrow-root; but this is not the case in commerce, the whole passing as W. I. arrow-root irrespective of the place of its production.

=Arrow-root, Eng'lish.= Potato-starch.

=Arrow-root, Portland.= From the underground tubers of _arum maculatum_ (Linn.) or wake-robin.

=Arrow-root, Tahi'ti.= Tacca starch or Otaheite salep; from the tubers of _tacca oceanica_.

=ARSE''NIATE.= _Syn._ AR'SENATE; ARSE''NIAS, AR'SENAS, L.; ARSÉNIATE, Fr.; ARSE''NIKSAURE SALZE, Ger. A salt consisting of AsO_{4} and a metal or other basic radical; _e.g._, ammonio-magnesium arseniate, NH_{4}Mg_{9}AsO_{4}.

=AR'SENIC= (-se-n[)i]k). As. _Syn._ ARSENIUM; ARSEN'ICUM, ARSE'NIUM, L.; ARSENIK, A.-METALL, Ger. ARSENICO, Sp., It. The brittle, grey-coloured metal, or metalloid, which forms the base of the white arsenic and orpiment of commerce. Discovered by Geber in the eighth century, but first accurately described by Brandt (A.D. 1773). The poisonous properties of arsenious acid were not generally known for some centuries after its discovery. As a medicine it was first employed in intermittents in Hungary.

_Sources._ Arsenic is peculiar to the mineral kingdom. The metallic arsenic of commerce is obtained by roasting arsenical pyrites (MISPICKEL), in earthen tubes, or in tubular earthen retorts; the arsenic sublimes, and sulphuret of iron remains behind. On the small scale it is prepared by sublimation from a mixture of arsenious acid and charcoal or black flux. Combined with oxygen it frequently exists in mineral waters; and, in a larger quantity, in certain rivulets and streams.

_Prep._ A mixture of arsenious acid, 1 part; and black flux, 2 or 3 parts; is exposed to a low red heat in a Hessian crucible over which is luted a deep empty crucible, or an earthen tube, to receive the metal; the latter being kept as cool as possible. Charcoal or even oil may be substituted for black flux, and a retort of hard glass may be used, with the same result. Or the following method may be used:--White oxide of arsenic, of commerce, 2 dr.; is placed at the sealed end of a hard German-glass tube (1/2 × 18 inches), and covered with about 8 inches of dry and coarsely powdered charcoal; the portion of the tube containing the latter is then raised to a red heat, whilst a few ignited coals are placed beneath the oxide to effect its slow sublimation. The sublimed metal gradually attaches itself to the inside of the tube at its cool extremity. A small charcoal furnace similar to that used for organic analysis should be employed, and the process conducted under a flue to carry off any fumes that may escape. The open end of the tube should be loosely closed with a cork.

_Prop._ Very brittle, so much so that it may be easily powdered in a mortar; lustre highly metallic; colour steel-grey or bluish-white; texture crystalline; crystals rhombohedrons; sublimes, without fusion, at 356 to 360° Fahr., (and slowly at lower temperatures), in close vessels unaltered, but when exposed to the air with conversion into arsenious acid; at a higher temperature, in open vessels, it burns with a pale-blue flame. Its vapour or fumes have a characteristic alliaceous odour; it is slowly oxidised and dissolved by boiling water; but may be preserved unchanged in pure cold water; it rapidly tarnishes in the air, particularly when moist, a black film, consisting of metallic arsenic and arsenious acid forming on its surface; with chlorine, iodine, sulphur, and hydrogen, it unites to form definite compounds. With oxygen it forms acids, but no basic oxide. It combines with the metals in a similar manner to sulphur and phosphorus, the latter of which it resembles in many respects. These compounds are termed AR'SENIDES, formerly ARSENIURETS. Sp. gr. 5·7 to 5·9; sp. gr. of vapour, 1·0362.

_Uses, &c._ With copper it forms a white alloy (PACKFONG); and it is added to some other alloys to increase their whiteness, hardness, and fusibility. In _medicine_ it is only used in combination. In the metallic state it is inert; but, from its great affinity for oxygen, it rapidly becomes oxidised and poisonous; and hence acts as a powerful poison when swallowed, or when rubbed on the skin. Its fumes are also highly poisonous. See ARSENIOUS ACID (and _below_).

=Arsenic, Tribro'mide of.= AsBr_{3}. _Syn._ TERBRO'MIDE OF ARSENIC, SESQUIBRO'MIDE OF A.; ARSEN'ICI BROMI'DUM, L. _Prep._ Add metallic arsenic, in powder, cautiously and in a very small quantity at a time, to pure bromine, contained in a vessel set in ice or a freezing mixture, until light ceases to be emitted; then cautiously distil into a well-cooled receiver.

_Prop., &c._ Solid below 68° Fahr.; above it, a yellowish fuming liquid, which boils at 428° Fahr.

=Arsenic, Trichlo''ride of.= AsCl_{3}. _Syn._ CHLO''RIDE OF A., ARSEN'ICI TERCHLORI'DUM, &c., L. _Prep._ 1. From a mixture of white arsenic, 1 part; and bichloride of mercury, 6 parts; both in powder, carefully distilled into a well-cooled receiver.

2. Gently boil powdered white arsenic for some time in hydrochloric acid to which a little nitric acid has been added; then concentrate cautiously by evaporation, and distil as before. It is also produced, with the disengagement of heat and light, when powdered metallic arsenic is thrown into gaseous chlorine.

_Prop., &c._ A colourless, volatile, highly poisonous liquid, decomposed by water into arsenious acid and hydrochloric acid. It has been employed as a caustic in cancer and venereal warts; but its use requires the greatest caution.

=Arsenic, Flu'oride of.= AsF_{3}. _Syn._ ARSENIC TRIFLUORIDE, TERFLU'ORIDE OF ARSENIC. A fuming volatile liquid, prepared as the bromide.

=Arsenic, Trii'odide of.= AsI_{3}. _Syn._ TERIODIDE OF ARSENIC, IODIDE OF ARSENIC; ARSEN'ICI IODI'DUM, A. TERIODI'DUM, L.; ARSENIC IODURE, &c., Fr. _Prep._ 1. From finely-pulverised metallic arsenic, 2 parts; iodide, 11 parts; mixed and gently heated in a bent glass tube, or a suitable retort, until combination is complete; the heat being then raised, and the sublimed iodide collected, and at once put into a well-stopped phial.

2. Arsenic, in fine powder, 1 part; iodine, 5 parts; triturate them together, place the mixture in a small flask or retort just large enough to contain it, and apply a gentle heat until liquefaction is complete, avoiding the formation of iodine vapour; when the odour of iodine is no longer perceptible, and the mass assumes a reddish-yellow colour and crystallises on the sides of the vessel, the operation is complete, without having recourse to sublimation. A very easy and excellent process.

_Prop., &c._ A deep orange-red, crystallisable solid; soluble in water, and highly volatile and poisonous. Its aqueous solution yields the iodine unchanged by rapid evaporation, but when slowly concentrated and set aside, white pearly plates are obtained, consisting of arsenious acid and the teriodide. As a medicine it combines the properties of both arsenious acid and iodine, but its use requires great caution. It has been successfully employed by Dr A. T. Thomson, Biett, and others, in obstinate skin diseases (lepra, impetigo, herpes, lupus, psoriasis, &c.), and in real or stimulated cancer.--_Dose_, 1/16 to 1/12 gr. (in pills or solution), gradually increased to 1/6 or even 1/3 gr. (A. T. Thomson.) Externally, 2-1/2 gr., to lard 1 oz.; of which 1 dr. may be used at a time. (Biett.)

=Arsenic, Disulphide of.= As_{2}S_{2}. _Syn._ ARSENIC BISULPHIDE, BISUL'PHIDE OF A., RED SUL'PHIDE OF A., &c., REALGAR; RÉALGAL, ARSENIC ROUGE SULFURE, ORPIN ROUGE, &c., Fr.; ROTHES SCHWEFELARSENIK, &c., Ger. This substance is found native at Solfaterra, near Naples, and in several other volcanic districts; but that of commerce is often prepared by distilling arsenical pyrites, or a mixture of sulphur and white arsenic, &c., in the proper proportions, as noticed under REÄLGAR and RED PIGMENTS.

_Prop., &c._ A fusible, volatile substance; scarlet or ruby-red in mass, but orange-red in powder, by which it is distinguished from cinnabar; crystals, oblique rhombic prisms. Sp. gr. 3·3 to 3·6. Its chief use is as a pigment and in pyrotechny to make white fire. The factitious sulphide has not the rich colour of the native mineral, whilst it is much more poisonous. It is improved by re-sublimation.

=Arsenic, Trisul'phide of.= As_{2}S_{3}. _Syn._ TERSUL'PHIDE OF ARSENIC, YELLOW SUL'PHIDE OF A., SESQUISUL'PHIDE OF A., OR'PIMENT; A. SESQUISULPHURE'TUM, ORPIMEN'TUM, L.; ORPIMENT, SULFURE JAUNE D'ARSENIC, &c., Fr.; AURIPIGMENT, OPERMENT, RAUSCHGELB, Ger. This sulphide, like the last, is found ready formed in nature; and is prepared artificially, by sublimation, from a mixture of arsenious acid and sulphur, as noticed under ORPIMENT and YELLOW PIGMENTS. It also falls as a precipitate when a stream of sulphuretted hydrogen gas is passed through an acid solution of arsenious acid or of an arsenite.

_Prop., &c._ Golden-yellow crystalline lumps, or a fine golden-yellow powder; crystals, right rhombic prisms; volatile; fusible; very soluble in pure alkalies, by which it is distinguished from sulphide of cadmium; and from trisulphide of antimony by being soluble in hydrochloric acid. The factitious sulphide (KING'S YELLOW) of the shops often contains 80 to 90% of white arsenic; and is, therefore, much more poisonous than the native trisulphide. Sp. gr. (native) 3·44 to 3·60.

_Use, &c._ As a dye, as a pigment, and as an ingredient in fireworks, and in some depilatories. Silk, woollen, or cotton goods soaked in a solution of pure orpiment in ammonia, and then suspended in a warm apartment or stove-room, rapidly lose their ammonia, and become permanently dyed of a superb yellow colour. The native sulphides (both red and yellow) are much less soluble, and hence less poisonous, than those prepared artificially. They also possess the richest colour; and are, therefore, preferred by artists and dyers. In former times, orpiment, like realgar, was employed in medicine. See ARSENIC.

=Arsenic, Pentasul'phide of.= As_{2}S_{5}. _Syn._ SULPHARSEN'IC ACID, &c.; ARSEN'ICI PENTASULPHURE'TUM, &c., L. When a stream of sulphuretted hydrogen is transmitted for some time through a solution of arsenic acid, a precipitate of the PENTASULPHIDE is deposited after some hours' repose. Its formation is accelerated by boiling the liquid.

_Prop., &c._ It greatly resembles the tersulphide in its appearance and general properties.

=Arsenic, White[double-dagger].= See ARSENIOUS ANHYDRIDE.

=Arsenic, Yell'ow.= Trisulphide of arsenic.

=ARSENIC ACID.= H_{3}AsO_{4}. _Syn._ ACIDUM ARSEN'ICUM, L.; ACIDE ARSÉNIQUE, Fr.; ARSENICSÄURE, Ger.

_Prep._ 1. Arsenious acid, in fine powder, 2 parts; concentrated nitric acid, 6 parts; hydrochloric acid, 1 part; mix in a flask or tubulated retort, and digest, with heat, until solution is complete; after repose, decant the clear portion and evaporate, to the consistence of a thick syrup.

2. Dissolve arsenious acid in hot hydrochloric acid, and when the solution is cold add concentrated nitric acid, in small quantities at a time, until red vapours cease to be evolved, then proceed as before.

_Prop._ Thick syrup, occasionally forming clear transparent crystals, very deliquescent, readily soluble in water, and converted by heat into the anhydrous acid. Extremely poisonous.

=Arseniates.= _Prep._ Most of the metallic arseniates may be formed by adding a solution of a soluble salt of the metal to another of an alkaline arseniate, as long as a precipitate falls; which must be collected, washed, and dried. The alkaline arseniates may be prepared by adding the base or its carbonate to a solution of the acid, to alkaline reaction, and then evaporating and crystallising the liquid.

_Prop., &c._ The arseniates of the alkalies are soluble in water; those of the earths and metals insoluble, except in acids. They are isomorphous with the corresponding phosphates.

_Tests._ Nitrate of silver added to the solution of an arseniate gives a highly characteristic reddish-brown precipitate, which distinguishes it from arsenious acid. Nitrate of lead gives a white precipitate, and the salts of copper greenish-blue ones. Pure lump-sugar dissolved in an aqueous solution of this acid becomes, in a few hours, of a reddish colour, and afterwards of a magnificent purple. Heated with charcoal it evolves a garlic-like odour, and is reduced to the metallic state. The suspected liquid being treated with sulphurous acid and boiled for a short time, the arsenic acid loses oxygen and is converted into arsenious acid, which may be tested for as such. Sulphuretted hydrogen does not precipitate a solution of arsenic acid, or an acidified arseniate, until after the lapse of several hours; and alkaline and neutral solutions not at all.

=ARSENIC ANHYDRIDE.= As_{2}O_{5}. _Syn._ ANHYDROUS ARSENIC ACID, ARSENIC ACID; ACIDUM ARSENICUM, L.; ACIDE ARSÉNIQUE, Fr.; ARSENIKSÄURE, Ger. Best prepared by igniting the arsenic acid, in a platinum crucible, at a low red heat, as long as water is given off.

_Prop._ White deliquescent substance, and violent poison, readily soluble in water to the acid.

=ARSENIOUS ACID.= See ARSENIOUS ANHYDRIDE.

=ARSE''NIOUS ANHYDRIDE.= As_{2}O_{3}. _Syn._ AR'SENIOUS ACID, AR'SENIC, WHITE A.; ACIDE ARSÉNIEUX, ARSENIC BLANC, OXYDE, Fr.; ARSENIGSÄURE, ARSENICHSTE S., Ger.; ARSENICO BIANCO, It.; A. BLANCO, Sp. The arsenic, or white arsenic, of the shops.

_Sources._ The white arsenic of commerce is principally imported from Germany, where it is obtained in the process of roasting arseniuretted cobalt ores, in making zaffre. At Altenburgh it is procured from arsenical iron pyrites (mispickel); and at Reichenstein from native arsenide of iron. About 900 to 1000 tons are also annually collected at Cornwall, being principally a secondary product of the process of roasting grey copper ore and white mundic. The British arsenic works in that county are perhaps the finest in the world. The usual plan is to roast the powdered ore in muffle-furnaces; by which its arsenic is converted into arsenious anhydride, which escapes as vapour (smelting-house smoke), and passing into the condensing-chambers, is deposited in a pulverulent state, forming the flowers of arsenic, or rough white arsenic, of the smelters, (the giftmehl or poison-flour of the Germans). The crude article obtained in this way is purified by re-sublimation in suitable iron pots or other iron vessels, before it is fit for sale. It then forms a semi-transparent vitreous cake, which gradually becomes opaque, and of snowy whiteness, by exposure to the air, and at length acquires a more or less pulverulent state on the surface.

In Silesia the crude arsenious anhydride obtained from arsenical pyrites is refined by sublimation as follows:--For this purpose the cast-iron vessels (_a_) are employed. Upon these are placed iron rings or collars (_b_, _c_, _d_) and a hood (_e_), communicating by means of tubes with a series of chambers, of which the first only is shown in _i_. The flanges of the cast-iron collars and all other joints having been thoroughly luted, the fire is lighted and the heat so increased as to cause the semi-fusion of the arsenious anhydride, which, after cooling, exhibits a peculiarly porcelain-like appearance, at first being as transparent as glass.

_Prop._ Crystals (obtained by careful sublimation, or by cooling a boiling aqueous solution), usually transparent, regular octahedrons (fig. 1), but sometimes, though rarely, assume the form of tetrahedrons (see 2). When prepared on the large scale it forms large, glassy, colourless or yellowish-white, transparent or semi-transparent cakes or porcelain-like masses (vitreous arsenious anhydride, glacial a. a.), which soon becomes opaque on their exterior, and often friable and pulverulent; odourless; volatilises at 380° Fahr.; fumes odourless, unless carbonaceous organic matter be present, when they smell strongly like garlic; heated under pressure it liquefies and forms a transparent glass; taste faintly sweetish, with a slight acidity and astringency, not perceived until some minutes after being swallowed. The opaque variety is soluble in 80 parts of water at 59° Fahr., and 7·72 parts of boiling water; but on cooling to 60°, only about one third of this quantity continues in solution. The transparent variety is soluble in 103 parts of water at 59°, and 9·3 parts of boiling water. Both soluble in alcohol, syrups, oils, and spirits, and freely so in alkaline lyes and hydrochloric acid; organic matter generally impedes its solution; solutions redden litmus; heated with organic matter it is reduced to the metallic state. Sp. gr. 3·5 (lowest opaque var.) to 3·8 (highest transp. var.).

=Arsenites.= True arsenious acid (HAsO_{2}) has never been obtained in a satisfactory condition, but its salts are readily obtained by dissolving arsenious anhydride in a solution of the base, or by double decomposition. They are generally white, nearly all insoluble, except those of the alkalies, and all soluble in acids.

_Tests, Detec., &c._ Owing to the importance of the subject, and for convenience and facility of reference, the leading tests for the arsenites and arsenious anhydride are noticed alphabetically below; to which a few general remarks on their application, under the various circumstances that occur to the chemist and toxicologist, are appended. When not otherwise stated, it is to be understood that they are to be applied to pure, or nearly pure and colourless solutions of arsenious acid or the arsenites. _Ammonio-nitrate of silver_ gives a well-marked yellow precipitate of arsenite of silver in an aqueous or arsenious anhydride solution which is soluble in ammonia and in dilute nitric acid.

_Crystallisation Test._--A very minute quantity of arsenious acid placed in a small tube (arsenic-tube), and heated in the flame of a spirit lamp, gives a crystalline sublimate, which collects on the cooler portion of the tube, and which, when examined by a pocket lens, is found to consist of sparkling octahedral crystals (see _engr._)

_Ellis's Test._--This is a modification of the 'nascent hydrogen test,' in which the suspected gas is passed through a tube containing slips of copper leaf or riband, or still better pure oxide of copper, gently heated; the end of the tube communicating with the atmosphere being drawn to a capillary size, at which the gas may be inflamed and tested, as in 'Marsh's Apparatus.' (See _engr._) If arsenic be abundant in the gas, the copper will be almost instantly covered over with a coating of metallic arsenic; and after continuing the heat for a few minutes it will present a beautiful silvery surface, and may then be submitted to further examination.

_a_, Flask containing the suspected fluid, dilute sulphuric acid,
and zinc.
_b_, Funnel.
_c_, Tube containing the copper-leaf or c.-riband, and heated by
the lamp _d_.
_e_, Support.
_f_, Capillary end of tube _c_, with the gas inflamed.]

_Lassaigne's Test._ (Adopted by the French Academy.) This consists in passing the gas generated in the suspected liquid, through a solution of nitrate of silver. (See _engr._) When arsenic is present black flocculi of metallic silver are deposited, and arsenious acid remains in solution mixed with nitric acid and some arsenide of silver. The filtered liquor, treated with ammonia, will now give a characteristic yellow precipitate of arsenite of silver; or a little dilute hydrochloric acid may be cautiously added to precipitate any remaining nitrate of silver, and the liquid, after filtration, tested for arsenic either in a Marsh's apparatus, or with any of the liquid tests; or it may be evaporated to dryness, when its arsenious acid will be converted into arsenic acid by the nitric acid present, and will then be found to give the usual brick-red precipitate of arseniate of silver with a solution of the nitrate of that metal. See MARSH'S TEST.

_a_, Bottle containing dilute sulphuric acid, zinc, and suspected
fluid.
_b_, Funnel for supplying the bottle with acid.
_c_, _c_, Supports.
_d_, Tube filled with asbestos.
_e_, Bent tube to convey the liberated gas.
_f_, Glass vessel containing a solution of nitrate of silver.]

_Marsh's Test._ Some of the suspected liquid is mixed with dilute sulphuric acid until strongly acid, and is then poured upon some pure granulated zinc, or clippings or other small pieces of zinc, previously placed in the apparatus; hydrogen gas is immediately evolved, and, if arsenic be present, unites with it, forming arseniuretted hydrogen gas, which escapes by the aperture _b_ (see _engr._), and may be recognised as follows:--

It possesses a garlic-like odour.

It burns with a bluish-white flame and emits a whitish smoke.

_a_, _a_, Bent glass tube, containing dilute sulphuric acid, zinc,
and suspected liquid.
_b_, Stop-cock and jet.
_c_, Plate of glass to receive the stain.
_d_, Support.
_e_, _e_, Bands to keep the tube upright.]

If a piece of window-glass, or a white porcelain plate or saucer, be held a short distance above the flame, a fine pulverulent film of arsenious acid is deposited on it. See (fig.) _above_.

If the cold plate be held in the flame, so as to slightly impede the combustion of the gas, a blackish-brown deposit of metallic arsenic is obtained, more or less deep, brilliant, and glistening. Both these deposits may be obtained simultaneously by holding nearly vertically over the flame a glass tube about 8 or 10 inches long and 3/8ths of an inch in diameter. See (fig.) _above_.

A solution of arsenious acid may be obtained by letting the flame play upon 3 or 4 drops of water placed on the under side of the piece of glass or china, to which the liquid tests may be then applied. Another plan is to apply drops of the liquid tests to the plate as above, and to let the flame play on them successively.

The true arsenical spot or film is of a blackish-brown colour, and generally of a very deep hair-brown, usually surrounded at the circumference, with a white film of arsenious acid; whilst that of antimony, which in some points is similar, is of a deep black colour, and but feebly lustrous, and, when viewed by transmitted light, appears smoky black; whereas an arsenical spot viewed in the same way appears brown. It is further distinguished from others by--Treated with concentrated nitric acid, it instantly disappears, leaving upon the surface of the liquid traces of the metal, which only dissolve on the application of heat. This solution, gently and carefully heated, leaves a white residuum, which, when cold, gives with a concentrated solution of nitrate of silver a dull-red precipitate of arseniate of silver.--The nitric solution treated with a few drops of sulphurous acid, and subsequently with sulphuretted hydrogen, gives a canary-yellow precipitate of trisulphide of arsenic, which readily redissolves, forming a colourless solution with ammonia.--The arsenical spot, when heated, is turned bright yellow by sulphuretted hydrogen, and is then readily dissolved, as before, by ammonia, and by its bicarbonate; whereas one of antimony is turned of a deep orange-red, or reddish-brown, by sulphuretted hydrogen, is not readily dissolved by ammonia, and is scarcely or not at all affected by bicarbonate of ammonia.--It is freely soluble in and removed by hypochlorite of soda; a reagent which does not affect antimonial spots. Heated by a flame of pure hydrogen an arsenical stain rapidly disappears. A mixed stain of antimony and arsenic does not disappear by the action of the last two reagents, and is shown to contain arsenic by the two first tests above. When hydrochloric acid is present zinc stains are sometimes formed, but they do not resemble those from arsenic. The flame which produces it is very pale blue or bluish-white; whereas antimoniuretted hydrogen burns with a pale green or greenish-yellow flame, and a white smoke, both of which are characteristic.

_Obs._ Marsh's test is admirable for its simplicity, delicacy, and trustworthiness, as well as for the ease of its application. It is adapted to all liquids, whether colourless or coloured, which are not so glutinous as to inconveniently froth during the extrication of the hydrogen.[79] Various modifications of the original apparatus have been proposed to obviate this difficulty; among which the one chiefly deserving notice is figured in the margin. It consists of a bent tube having two large bulbs blown in it, and fitted with a stop-cock and jet in the usual manner. In this case the grains or fragments of zinc are put into the lower bulb (_a_). It is, however, worthy of remark, that, with ordinary care and skill, a simple wide-mouthed bottle, furnished with a tube and cock, will often be found to answer quite as well as more costly apparatus; as the fluid is less liable to froth than in a narrow tube. Even a common quinine-phial, or a 4-_oz._ or 6-_oz._ medicine phial, fitted with a piece of glass tube of very small bore, or even with a piece of a common tobacco-pipe, for a burner (see _engr._), may be used when no more convenient instrument is at hand.

[Footnote 79: Animal tissues and liquids containing organic matter are best prepared for testing for arsenic by Marsh's test, in the following manner proposed by Odling:--The tissue, or the residue obtained by the evaporation of a liquid over a water-bath, is to be thoroughly dried at a temperature of about 212° F., then ground to powder or cut up into small pieces, next drenched with the strongest hydrochloric acid and allowed to stand twenty-four hours in a warm place, and finally distilled. The distillate will contain arsenic (if it existed in the material under examination) comparatively free from organic matter, and is, therefore, in a fit state to be introduced into Marsh's apparatus, as the organic matter, which is the cause of frothing, has been removed.]

A film of oil placed on the surface of the liquid tends considerably to lessen the frothing.

_Objec., precau., &c._ Objections have been raised to this mode of testing, from the great frothing which often occurs with organic mixtures, and from antimony and imperfectly charred organic matter also forming crusts somewhat resembling, to the inexperienced eye, those produced by arsenic. But these objections are invalid, because there are easy means of purifying the liquid before testing it, and of discriminating between true arsenical spots or deposits and false ones. Another objection is, that both zinc and sulphuric acid sometimes contain arsenic; but to obviate this difficulty, we have only to use them when perfectly pure; and to test them by means of the apparatus before pouring the suspected liquid into it. Indeed, these objections apply with equal force to all those tests which depend on the production of nascent hydrogen. The precaution necessary to success, and to reliable results, is to set the apparatus with simple zinc, acid, and water, and after it has worked a short time to test the evolved gas for arsenic (as above); when, if no trace of that substance is detected, the suspected fluid, in which the organic matter (if necessary) has been destroyed by any one of the methods hereinafter pointed out, may be added, and the operation continued. Care should also be taken not to light the jet of gas before all the atmospheric air is expelled from the apparatus, as without this precaution an explosion may take place.

_Modification of Marsh's Test._--_Davy._ This process consists in the use of sodium amalgam instead of zinc and sulphuric acid, both of which are liable to be contaminated with arsenic. Sodium, on the other hand, has never been found to contain arsenic, and mercury only very rarely; but should it exist in that metal, it can be easily removed by digesting the mercury in dilute nitric acid, and afterwards well washing it with water.

One part by weight of sodium to 8 or 10 parts of mercury forms a very good amalgam. The mercury is placed in a test-tube, and the sodium gradually added in small portions; the metals readily combine, forming an alloy, liquid whilst hot, but hard and brittle when cold.

The author uses this amalgam by placing the suspected solution, or solid substance, along with a little water in a test-tube, then adding a small piece of amalgam about the size of a grain of wheat, and quickly covering it with a piece of white filtering paper or the lid of a porcelain crucible moistened with a dilute solution of silver nitrate slightly acidified with nitric acid. If arsenic is present, a dull black or deep brown stain on the paper or porcelain will be developed on the moistened part, owing to the silver being reduced to the metallic state by the arseniuretted hydrogen. The solution may be made by dissolving 20 gr. of nitrate of silver in an ounce of distilled water acidulated with 2 drops of strong nitric acid.

It is advisable to place between the moistened paper or lid and the tube a small disc of bibulous paper, to prevent any particles of the liquid producing minute black spots, and thus interfering with the results. 1/1000th part of a grain of arsenious acid in 1 c. c. of distilled water gives a very decided effect in a few moments, but much smaller quantities may be detected, _e.g._, the 1/100000th or even 1/1000000th part of a grain in 1 c. c.

This method is applicable not only to arsenic as arsenious acid, but also to other compounds of arsenic, soluble or insoluble in water, _e.g._, orpiment and realgar, the alkaline arsenates, and even the metal itself if in powder. Organic matter interferes but very little with this method. Antimony, as in Marsh's process, will produce, with the sodium amalgam, results similar to those of arsenic; this, when brought into contact with the nitrate of silver, forms a black antimonide of that metal.

Fleitmann, however, pointed out that antimoniuretted hydrogen is not evolved from strongly alkaline solution, and, as in this case, the action of the sodium amalgam is to render the mixture quickly alkaline, only a very small quantity of antimony present will be evolved, and by previously rendering the mixture strongly alkaline the evolution of that gas may be almost entirely prevented.

It may be occasionally necessary to determine whether the stains on the paper moistened by the silver solution are due to arsenic or antimony. It is then best to digest the paper-stain in sulphide of ammonium, the metal present being converted into a sulphide, and dissolving in the excess of the alkaline salt, leaving the silver sulphide undissolved; the alkaline solution when evaporated will, in the case of arsenic, leave a bright yellow residue, almost insoluble in hydrochloric acid; whereas in the case of antimony an orange-coloured residue will remain soluble in that acid. Dr Russell observes that hydrogen alone is capable of reducing silver solution to the metallic state, but acknowledges that this action is exceedingly slow. Pellet, on the other hand, maintains that pure hydrogen when passed through solutions of soda and nitrate of silver has no action at the ordinary temperature; but he states that the silver salt which has been fused possesses an alkaline reaction in solution, and hydrogen thus produces a slight precipitate, which can be prevented by adding a drop or two of nitric acid.

Davy, however, found in his experiments only the faintest possible effect of the reducing action of pure hydrogen in solutions of caustic soda and nitrate of silver.

Finally, the author mentions that where paper is used with the silver solution we must not forget that the silver alone will after some time blacken the paper, especially if exposed to light; but this gradual change is very unlike the quick effect produced by arseniuretted or antimoniuretted hydrogen. ('Chem. News,' xxxiii, 58-63.)

_Nascent Hydrogen Test._ The apparatus used may be similar to that figured in the _engr._ The plan followed in the laboratory of Giessen is to heat the long tube through which the gas passes to redness in several parts, to produce distinct metallic mirrors; and then to remove the tube from the hydrogen apparatus and transmit a very feeble stream of dry sulphuretted hydrogen through it, the metallic mirrors being at the same time heated by means of a common spirit lamp from the outer towards the inner border or extremity. If arsenic alone is present, yellow trisulphide of arsenic is formed within the tube; if antimony alone is present, an orange-red or black trisulphide of antimony is produced; and if the mirror consists of both metals, the two sulphides appear side by side, the sulphide of arsenic, as the more volatile, lying invariably before the sulphide of antimony. If dry hydrochloric acid gas be now transmitted through the tube, without application of heat, no alteration will take place if sulphide of arsenic alone is present, even though the gas be transmitted through the tube for a considerable time. If sulphide of antimony alone is present, this will entirely disappear; and if both sulphides are present, the sulphide of antimony will immediately volatilise, whilst the yellow sulphide of arsenic will remain. If a small quantity of ammonia be now introduced into the tube, the sulphide of arsenic is dissolved, and may thus be readily distinguished from sulphur, which perhaps may have separated.