Prof. Giseke's ObservatioJis on the Tests fur Arsenic. 255 



— in which, however, we must suppose a much stronger affinity 

 between the arsenic and the ammonia than between the arsenic 

 and the potash or soda, — I have been requested by Professor 

 Schweigger to make a series of experiments on the decom- 

 position of arsenite of hme by the salts of ammonia. The fol- 

 lowing are the results. 



A. I precipitated some arsenious acid with lime-water, and 

 added to this liquid, in which the arsenite of lime was suspended 

 in Avhite flakes, the following ammoniacal salts in solution; 

 viz. the muriate, nitrate, acetate, and sulphate. Each of these 

 produced a solution of the arsenite of lime and clarified the 

 liquid. But when I added to this liquid containing the arsenite 

 of lime in flakes, phosphate or carbonate of ammonia, an effect 

 was produced on the lime, but a deposit always remained. 

 This shows evidently the existence of a double affinity, since 

 the phosphoric and carbonic acids became precipitated in com- 

 bination with the lime, but with the other ammoniacal salts the 

 solution remains clear, as may be seen from the following ex- 

 periments. 



a. The precipitate formed by carbonate of anmionia effer- 

 vesced in acetic acid, and diluted with water gave with oxalic 

 acid a white precipitate of oxalate of lime. 



b. By adding sulphuretted hydrogen to the clear superna- 

 tant liquid a yellow tinge was produced ; with nitrate of silver 

 a yellow, and with lime-water a white precipitate. 



c. The solution above the precipitate produced by phos- 

 phate of ammonia, gave with sulphuretted hydrogen a yellow 

 tinge ; with nitrate of silver a yellow, and with lime-water a 

 white precipitate. 



B. Arsenite of lime newly precipitated was filtered oflT, and 

 washed with distilled water : this pappy substance was then put 

 into solutions of acetate, muriate, nitrate, and sulphate of am- 

 monia, and completely dissolved ; but in phosphate or carbon- 

 ate of ammonia a precipitate remained, as described above. 



C. The arsenite of lime being well dried was not dissolved 

 by nitrate, acetate, or muriate of ammonia, at common tem- 

 peratui'es; but when boiled the solution became quite clear. 

 But if boiled with natmal phosphate of ammonia, a precipitate 

 of phosphate of lime remained. 



2. On the Detection of Arsenic bj/ vicans of lodinc-st arch. 



Brugnatelli was the first who stated that iodine-starch might 

 be applied as are-agent for arsenious acid. His essay on the 

 subject may be found in the Journ.f. Chcm. u. Phi/s. vol. xx. 

 p. 56. According to him, iodine-staixh is deprived of co- 

 lour by arsenious acid and by solution of sublimate; but the 



blue 



