IN CASES OF POISONING. 269 



into the bottle, which is then half-filled with distilled 

 water : when the apparatus is all arranged, distilled 



Fig. 42. 



concentrated sulphuric acid is added in small portions 

 by the funnel tube b, very gradually, so that the mix- 

 ture may not become too hot, lest sulphuretted hydro- 

 gen should be formed. The evolution of hydrogen is 

 allowed to proceed until it is judged that all atmos- 

 pheric air is expelled, and that the apparatus is per- 

 fectly filled with hydrogen. 



The narrow delivery-tube is then heated to redness 

 at e, for at least half an hour, by a spirit lamp with a 

 double draught, or a powerful gas-burner, the evolu- 

 tion of hydrogen being constantly maintained by 

 adding acid from time to time. In this way, the acid 

 and zinc are tested for any trace of arsenic which 

 might be present. If they are pure, no incrustation 

 will be deposited at the ignited spot, e. If arsenic be 

 present, a metallic mirror is obtained at this portion 

 of the tube, and the acid and zinc cannot be used ; 

 even the apparatus must then be carefully cleaned, or, 

 better, replaced by a new one. In the same manner 

 any arsenic might be detected in the hydrochloric 

 acid, the chlorate of potassa (after having been com- 

 pletely converted by fusion into chloride of potas- 



23* 



