AKSK.Nlr. ])CTK(TION OK. 



Mi'. n!-:TK<TK>N 



ODO ooaqxnmd may be forum I. or one may be mixed with variable 

 quantities of hydrate of copi*r. 



4ranw<s o/skhNT (SAgO, AiO.) may b nude by mixing a solution of 

 titrate of silver with one of anenite of ammonia, potash, or swla. It 

 is of a fine ydlow colour; end the voluble salts of silver, like those of 

 copper, are occasionally uwd to afford corroborative evidence in cawa 

 of poisnainfl by arsenic. 



The srsraiam are in several cawa presented to ui by nature. Thus, 

 is Cornwall. araeoiaU of iron oocun in amaU green cubic crystals, and 

 be several beautiful varieties of aneniate of copper. Aneniate of 

 How. called phannaoolite by mineralogista, ia aometimeB, though rarely, 

 met with. 



The alkaline and earthy araeniatei are generally procured either by 

 direct combination or by double decomposition; and the metallic 

 fMuates usually, if not alwaya, by the Utter method. We shall 

 describe the aneniatea in the same order aa the arsenites. 



Armiate of ammonia (2NH.O, HO, AsO,). This Bait ia prepared by 

 adding the alkali to a rather concentrated solution of the acid, until a 

 precipitate appeare. If this and the solution be exposed to spontaneous 

 evaporation, large rhombic crystals are obtained. These crystals, when 

 exposed to the air, lose half of their base, and are converted into mono- 

 mm m*li nf ammonia When subjected to distillation, the ameniate of 

 Minim decomposes as it becomes dry, ammonia, water, and nitrogen 

 gas are obtained, and the araenic is reduced. 



The mo*o-ar*auate of ammomia (NH.O, 2HO. AsO.) may not only 

 be obtained, as bore-mentioned, by exposing the neutral salt to the 

 air, but abo by adding arsenic acid to it. By alow evaporation, large 

 octahedral crystals are formed: when heated, it yields arsenioua acid, 



Tr^arteniatt of polo* (8KO, AsO,). It may be procured by satu- 

 rating the acid with the alkali. It is an uiicrystallUable deliquescent 

 mass, and may also be obtained by fusing a mixture of arsenious acid 

 and hydrate of potash. The arsenious acid acquires oxygen from the 

 decomposed water, hydrogen gas being evolved, and sometimes a 

 portion of the arsenioua acid is reduced. 



MoHMtnaualt ofpotatk (KO, AsO,) is usually prepared by heating 

 a mixture of arsenious acid and nitrate of potash. The nitric acid yields 

 oxygen to the arsenious, so as to convert it into arsenic acid, which 

 uniting with the potash, the mono-arseniate is formed. The mass, 

 when dissolved in hot water, yields transparent crystals of the salt 

 The solution reddens litmus paper. The salt suffers no change by 

 exposure to the air : its taste is cooling and saline, somewhat like that 

 of nitrate of potash. The crystals contain water. 



The aneniate and mono^tneniale of orf are cryntallisable salto, but 

 which do not require any particular notice. The arteniatt* of the 

 earths are not of importance. 



Aneniate of baryta, and aneniate of ttrontia are both soluble salts : 

 they are entirely artificial compounds, and applied to no use. AVitli 

 respect to the metallic arseniates, we have already stated that the 

 rseniatea of iron and copper occur in Cornwall : they may also be 

 formed artificially. The aneniate of tilver is of a brick-red colour, 

 while, as already noticed, the anenitt is yellow. Some use is made of 

 this difference in processes for detecting the presence of araenic. Most 

 metallic aneniates are insoluble in water, but dissolved by adds. As 

 to the general properties of arsenical acids and salU, we shall merely 

 remark that both the ackls are precipitated yellow by sulphuretted 

 hydrogen ; the .arsenites are precipitated yellow by the salta of surer, 

 and green by those of copper; while the aneniates are thrown down red 

 br the silver sahs, and blue by the copper ones. 



ARSENIC, DETECTION OK. Of all substances, arsenic is that 

 which has most frequently occasioned death by poisoning, both by 

 accident and design; we shall therefore briefly state the methods of 

 ascertaining its presence. 



Supposing a white powder to hare been found under suspicious 

 circumstances, the process to which it is to be subjected is that of 

 reduction to the metallic state and sublimation, and for this purpose 

 we employ small glass tube, a spirit lamp and black flux, or fresh 

 burnt and powdered charcoal. The tube should be thin, closed at one 

 nid, about one-fourth of an inch in diameter, and three to four inches 

 long; those known by the name of tat tata answer the purpose 

 extremely well. Black flux is a mixture of eharooal and carbonate of 

 pots*, prepared by deflagrating two parts of bHartrate of potash and 

 one part of nitrate in a crucible. It is to be powdered, and imme- 

 diately put into a well-stopped bottle to prevent ita acquiring moisture 

 from the air; the charcoal which it contains is derived from the 

 decomposition of the tartaric acid, and the potash from that of the 

 Wtartrate and nitrate. Mix a small portion, a grain or two, or even 

 less, of the suspected powder with twice its quantity of the black flux, 

 ad convey the mixture to the bottom of the tube by means of a 

 trough of smooth writing paper, taking care that none remain adhering 

 to the sides of the tube. Put a paper plug loosely into the orifice of 

 the tub*, and twUt a piece of paper round the upper end of it, to 

 M a handle ; then expose the mixture to the flame of the spirit 



ban. The potash of the flux retains the snenious ari.l until it i 

 sufficiently heated to be decomposed by the charcoal. If the quantity 

 of arssnious old be extremely small, then it is better to drop it into 

 the tab*, and to 1st fall a Uttb powdered charcoal upon it. In a 

 very short time after applying beat as before, the charcoal combining 



with the oxygen of the arsenious acid, the reduced metal rises in 

 vapour, and condenses in the upper and cool part of the tube ; it has a 

 metallic appearance, and is of a brilliant dark steel-gray colour. 



Although this effect may be regarded as evidence of the presence of 

 arsenic, l)r. Turner ha improved upon it by showing tli.it the metal 

 may be easily re-converted to arsenioua acid, and exhibit tlie cliarao. 

 teristic form and propertied of that substance, although its weight may 

 not exceed one-hundredth of a grain. This change ia effected by holding 

 hat part of the tube which contains the arsenic about three-fourths of 

 an inch above a very small flame of the spirit lamp ; the metal again 

 sublimes, and re-combining with the oxygen of the air in the tube, 

 'onus well-defined crystals of araenious acid. 



If no solid arsenious acid should lie found, but is suspected to exist 

 n solution, either iu the food or in the contents of the stomach, thru 

 iheee materials, after being boiled with dilute hydrochloric acid, and 

 strained through calico, should be tested by one or more of the follow- 

 Ag processes. 



Rcnach't tat, Boil a portion of the strained liquid, obtained as just 

 mentioned, with bright copper turnings or strips of copper foil, fur 

 half an hour. If the surface of the copper become dull during thin 

 operation, the fragments must be carefully washed with distilled 

 water, dried at 212 , introduced into a clean and narrow glass tube, 

 and then heated nearly to redness. If a sublimate condense on the 

 cooler portion of the tube, it must consist either of arsenious acid or 

 metallic mercury ; the beautiful transparent octahedral crystals of tin- 

 former cannot, however, be confounded with the brilliant metallic 

 globules of the latter. 



Marth't Tat. This invaluable process for the detection of arsenic 

 depends upon the formation of araenuretted hydrogen, when any 

 solution containing arsenic is brought into contact with nascent liy- 

 drogen. To apply it, the strained liquid above mentioned is intro- 

 duced, together with a few strips of zinc, into 

 the apparatus figured in the margin, the zinc 

 being placed in the lower bulb. If the liquid be 

 not already sufficiently acitl to act readily upon 

 the metal, it may be rendered so by adding either 

 hydrochloric or sulphuric acid. On then inserting 

 the cork and closed stopcock, the gas evolved 

 gradually collects in the lower bulb, expelling 

 the liquid into the upper one, until the zinc is 

 left above the liquid, when further action of 

 course ceases. On now cautiously opening the 

 stopcock, the gas, which will be expelled by the 

 pressure of the column of liquid, must be ignited, 

 and the flame made to impinge upon the interior 

 of a small porcelain cup or basin. The pro- 

 duction of a brown or black stain upon that part 

 of the porcelain upon which the flame hag played, 

 proves the presence of araenic or antimony. If 

 now a small quantity of solution of chloride <>f 

 lime (bleaching-powder) be poured into the por- 

 celain cup so as to cover the stain, the latter will 

 disappear if it consist of arsenic. If the stain do 

 not disappear, antimony is present ; but the stain 

 may also have contained arsenic, as it ia impossible to i>cr.-.-i\ .- with 

 certainty, whether or not a portion only of the stain hiui dissolved. 

 Under these circumstances, to ascertain indubitably the presence of 

 arsenic, recourse must be 

 had to Klcitman' test, which 

 must be applied to another 

 portion of the original 

 strained acid liquor. 



PUitman't Te*t. This 

 simple and very valuable 

 tost is founded upon the cir- 

 cumstance that when :m 

 arsenical solution is heated 

 with excess of caustic soda 

 or potash, in contact with 

 nine, arsenurattod hydrogen 

 is evolved ; whilst by a simi- 

 lar treatment of an antimo- 

 nial solution, no utiiuoiiu- 

 rctted hydrogen is liberated. 

 It therefore affords a ready 

 means of detecting arsenic 

 with certainty, even in pre- 

 sence of antimony. 



The following is the me- 

 thod of applying this test. 

 A portion of the strained 

 liquid above alluded to is 

 placed in a test-tube, Pig. a, 

 containing a few fragments 

 of granulated cine. A strong 

 solution of caustic soda or 

 of caustic potash is then added until the liquid in strongly alkalis 

 the mouth of the tube being closed by a strip of filter j q-r, moistened 



