ARSENIC. 183 



How are ar- ' DISTINCTION BETWEEN ARSENIC AND 



tenicandan- ANTIMONY STAINS. If in testing for arsen- 

 Smguish i c > by the method above described, a metallic 

 cd - spot is obtained, the evidence of the pres- 



ence of arsenic is not entirely conclusive. A solution 

 of antimony, if substituted for arsenic in the experi- 

 ment, will give rise to the production of somewhat sim- 

 ilar stains. But the experimenter will find, on com- 

 paring the two kinds of spots, that they are of quite 

 different appearance. Those of antimony are of deep- 

 er black, and fainter lustre. Again, those of arsenic 

 are much more readily removed by heat. " Chloride of 

 soda," is a still more conclusive means of distinguish- 

 ing them. A solution of this substance will dissolve 

 the arsenic stains, while it leaves those of antimony 

 unaffected. The " chloride of soda," to be used in 

 the experiment, is prepared by adding an excess of car- 

 bonate of soda, to a solution of " chloride of lime," 

 and then filtering the liquid. 



448. ADDITIONAL TESTS FOR ARSENIC. 



Mention some . .. , 



additional A second test has already been given in 

 l^ t c s / or arse ' the paragraph on the preparation of me- 

 tallic arsenic, to which the student is re- 

 ferred. The formation of a yellow precipitate, on the 

 addition of hydro-sulphuric acid to a solution, also 

 renders it highly probable that arsenic is present. 

 If on drying the precipitate, and heating it with a 

 mixture of cyanide of potassium and carbonate of soda, 

 a metallic mirror is obtained, the inference of the pres- 

 ence of arsenic is confirmed. The process is to be 

 conducted as directed in paragraph 440. In this exper- 



