Dr. Penny and Mr. W. Wallace on Chloride of Arsenic. 363 



this testj as thus applied, for the detection of bichromate of pot- 

 ash has been fully shown in the fourth volume of the Quarterly 

 Journal of the Chemical Society of London. Taking the mean 

 of two well-executed experiments, it results that 100 parts of 

 chloride of arsenic correspond to 5-i"5 parts of bichromate of 

 potash. In order to deduce from this ratio the proportion of 

 arsenic existing in the chloride, similar experiments were made 

 wdth pure arsenious acid, which gave very nearly the proportion 

 of 100 of arsenious acid to 100 of bichromate of potash. From 

 these numbers it is evident that chloride of arsenic contains 

 41*25 per cent, of metallic arsenic. 



The amount of chlorine was estimated in the usual manner as 

 chloride of silver. 



The following table shows the composition of the chloride : — 



Theoiy. Experiment. 

 Arsenic .... 75 4.1-32 41-25 



3 equivs. Chlorine . 106-5 58-68 58-86 



181-5 10000 100-11 



It may be as well to mention, that the chloride prepared as 

 above had the specific gravity of 2*1766. It was strongly acid 

 to litmus paper, completely soluble in alcohol and in tether ; and 

 it was also observed to have the power of dissolving a very con- 

 siderable proportion of arsenious acid. 



The action of water on the anhydrous chloride is particularly 

 remarkable. It is stated by several writers, that the addition of 

 the proper quantity of water converts the anhydrous chloride 

 into a hydrate, having the formula AsCF, 3H0. Our attempts 

 to obtain this hydrSted compound proved unsuccessful. A known 

 quantity of the anhydrous chloride was mixed with a sufficient 

 proportion of water to convert it into the hydi-ate referred to, 

 and the two liquids well agitated. The mixture became per- 

 ceptibly wann, but on repose the greater part of the chloride 

 separated. Additional portions of water were then successively 

 added, the mixture being allowed to cool after each addition. 

 The chloride gradually diminished; and when the total quantity 

 of water amounted to about 18 equivalents to one of the chlo- 

 ride, the latter was found to be completely mixed. The resulting 

 fluid, which had the specific gravity of 1*53, is miscible with a 

 much larger quantity of water without any visible change, viz. 

 to the extent of nearly 18 equivalents additional, making a total 

 of 36 equivalents of water to one of anhydrous chloride. On the 

 further addition of water, however, a separation of arsenious acid 

 takes place. The specific gravity of the mixture containing 36 

 equivalents of water was 1-346. 



We have obtained some interesting results by the distillation 



