334 Simple method for the 



have become so generally known. But a much more serious 

 obstacle to the employment of the process in this country is 

 implied in the fact that an arsenical sublimate may be ob- 

 tained, and yet the arsenic be derived from other sources 

 than the suspected liquid ; for the zinc and sulphuric acid 

 employed in the process, are both liable to be impregnated 

 with arsenic, and hence become direct sources of error. The 

 ores of zinc frequently contain orpiment, which, being redu- 

 ced with the zinc, contaminates it with arsenic : Dr. Clark of 

 Aberdeen has even stated that he has not discovered a single 

 specimen of commercial zinc free from arsenic. Of late years 

 iron pyrites has been much employed in the manufacture of 

 oil of vitriol, and it occasionally contains traces of orpiment, 

 by which the acid also is contaminated with arsenic. The 

 difficulty of obtaining absolutely pure zinc and acid at an 

 out-station, in a case of emergency, is sufficiently obvious. 

 Re-distillation, both of the acid and zinc, can alone free them 

 from this very objectionable impurity ; and the means re- 

 quisite for such a process are still less likely to be attainable 

 at out-stations than Marsh's apparatus itself. The produc- 

 tion of arseniuret of hydrogen by the galvanic decomposition 

 of water, as suggested by Mr. Morton, excludes most effectu- 

 ally the presence of arsenic and other impurities from the 

 materials employed : but such a method, by complicating the 

 apparatus, could not be had recourse to in the circumstances 

 just alluded to. 



Such then being the advantages peculiarly adapting Reinsch's 

 process to the detection of arsenic in cases of suspected poi- 

 soning occurring in this country ; and it being the foundation 

 of the methods I have adopted for the detection of the poi- 

 sonous compounds of mercury and antimony, I shall briefly 

 explain the most simple and effective manner in which it may 

 be conducted, before passing to my own experiments. 



Reinsch's Process. — Any particles, having the appearance 

 of white arsenic, or of the grey fly powder, may be removed 





