Dr. Penny and Mr. "W. Wallace on Chloride of Arsenic. 365 



metallic arsenic in Eeinscli^s process appears to depend almost 

 entirely on the ready production of chloride of arsenic, which is 

 instantly decomposed on contact with copper. 



As the formation and escape of chloride of arsenic appear 

 therefore to occur with certainty when arsenious and hydrochloric 

 acids are heated together, it became interesting to inquire whether 

 similar results would obtain in presence of organic matters. 



Half a grain of arsenious acid was mixed with an ounce of 

 porridge, and an ounce of hydrochloric acid being added, the 

 mLxtm-e was distilled. The moment the mixture began to boU, 

 a slip of copper ribbon previously placed in the neck of the flask 

 was coated with metalhc arsenic. Nearly an eighth part of the 

 mixture was distdled over, one-half of which gave with sulphu- 

 retted hydrogen the well-known effect of a solution of arsenic. 



Again, two-tenths of a grain of AsO^ were mixed with an 

 ounce of porridge and three-fourths of an ounce of liCl, and the 

 mixture distilled as before. Three drachms of the distillate, 

 when tested by Marsh's process, afforded brilliant stains of 

 metallic arsenic. The distillate gave also a yellow precipitate 

 with sulphuretted hydrogen. 



Similar experiments were peiformed with cow's liver and with 

 common broth. The results were equally satisfactory. 



The foregoing experiments plainly indicate the availability of 

 the chloride of arsenic in medico-legal investigations for the 

 separation of the metal from animal and vegetable matters ; and 

 we are induced to think that its production by the direct agency 

 of hydi'ochloric acid will be found in practice to be moi'e conve- 

 nient than by distillation with sulphuric acid and common salt, 

 as recommended by Dr. Pyfe. It appears to be peculiarly suit- 

 able for the preparation of the liquid to be subjected to Marsh's 

 process. The chief precaution to be observed is to employ the 

 hydrochloric acid in sufficient quantity and of full strength. 



Several experiments were likewise made with sulphide of 

 arsenic. It is slowly decomposed by concentrated hydrochloric 

 acid, with the formation of chloride of arsenic ; but the distillate 

 is veiy apt to be contaminated with sulphide of arsenic, repro- 

 duced by the secondary action of the sulphuretted hydrogen 

 disengaged at the same time. As common orpiment, however, 

 usually contains arsenious acid, the present process seems also 

 applicable to those cases in which this substance may occur. 



We arc at present engaged with the examination of some sin- 

 gular compounds of chloride of arsenic. 



