184 



METALLOIDS. 



iment, the cyanide of potassium has the effect of retain- 

 ing the sulphur, while it allows the volatile arsenic to 

 pass and deposit above. 



449. Still another evidence of the pres- 



What is said 



of the garlic ence of arsenic, is afforded in the charac- 

 teristic garlic odor which is emitted by the 

 flame produced by burning arsenic, in the experi- 

 ment previously described, called Marsh's test. The 

 same odor is also obtained on sprinkling a little ar- 

 senious acid upon burning charcoal. 



Mention the 450. PREPARATIONS FOR THE ARSENIC 



preparations TEST> Before proceeding with the che- 



for the ar- 

 senic test? mical experiments for the detection of ar- 

 senic, some preliminary labor is com- 

 monly required, to bring the material to 

 be tested into proper form. It com- 

 monly consists of matters which have 

 been ejected from the stomach, or of the 

 contents of the stomach itself. If the 

 student wishes to begin at this point, in his experi- 

 ments, he may add a small portion of arsenic to 

 some bread and water, and proceed with this paste, in 

 his investigation. This mixture is to be diluted with 

 water, and saturated with chlorine, as in the process for 

 preparing a solution of this gas. Chlorine has the effect 

 of destroying a certain portion of the organic matter, 

 and rendering the rest floculent, so that the liquid may 

 be easily separated from it by filtration. It also brings 

 the arsenic perfectly into solution, as a chloride. This 

 solution is then filtered, and treated as directed in the 

 preceding paragraphs. 



