263 Dr. Wallace qn Brpmo-arseniom Acid. 



As Br^ + 3 AsO^. Analysis of three cMerent preparations gave, — 



Arsenic 4 = 300 49-02 



Bromine . 39-3 40-1 41-87 3 = 240 39'21 



Oxygen 9 = 72 11-77 



612 10000 



The application of a high temperature causes the decomposi- 

 tion of both of these compounds, with distillation of pure terbro- 

 mide of arsenic. A portion of the bromine is, however, tena- 

 ciously retained by the arsenious acid that remains behind. 



Action of Water upon Bromide of Arsenic. 



Bromide of arsenic cannot be dissolved in water without 

 causing the separation of a white precipitate. About three parts 

 of water at the boiling temperature are required for complete 

 solution ; but a much smaller quantity is sufficient if hydrobromic 

 acid is added. A boiling aqueous solution deposits, on cooling, 

 octahedral crystals of arsenious acid, which are quite free from 

 bromine. When the bromide is boiled with a quantity of water 

 containing hydrobromic acid, insufficient to dissolve the whole 

 of it, the portion that remains undissolved becomes viscid, and 

 acquu-es a dark-brown colour from its conversion into bromo- 

 arsenious acid. 



Hydrated Bromo-arseniotts Acid. 

 A cold solution of bromide of arsenic in water and hydro- 

 bromic acid gives, by evaporation over oil of vitriol, thin, white, 

 pearly crystals, which consist of the hydrated compound acid. 

 Analysis gave 40-55 per cent, of bromine, which agrees with 

 the formula 3 HO, As BrO^. 



A^rsenic .... 1 = 75 37-88 



Bromine. . . . 1 = 80 4040 



Oxygen .... 2 = 16 8-08 



Water .... 3 =_27 13-64 



198 100-00 



This compound does not appear to lose its water of hydration, 

 or at least not the whole of it, over oil of vitriol. 



AVhen bromide of arsenic is dissolved in boiling water contain- 

 ing a considerable quantity of free hydrobromic acid, the solution 

 on cooling gives no arsenious acid, but a compound of arsenious 

 acid with hydrated bromo- arsenious acid, having exactly the 

 constitution assigned to the coi-responding iodine salt. This 

 compound falls as a bulky precipitate consisting of white pearly 

 flakes, which have, when drained and dried by pressure between 

 folds of bibulous paper; a beautiful silky lustre. It contains, 



