﻿2 THOMSON, Presence of Arsenic in the Body. 



vaporised sulphuric acid filled the flask. A few drops of 

 nitric acid added to the very hot sulphuric acid quickly 

 destroy any remaining organic matter, leaving the arsenic 

 present in the 5 c.c. of clear sulphuric acid : 10 c.c. of pure 

 water were then added and this was evaporated till white 

 fumes again appeared in the flask when it was ready for 

 transferring to the electrolytic apparatus after being diluted 

 with 10 c.c. of pure water, all nitrous compounds having 

 been thus removed, the flask being rinsed with 5 c.c. of 

 pure water. 



The electrolytic apparatus is connected up so that the 

 current enters at the platinum anode and leaves at the 

 zinc kathode, 10 c.c. of dilute sulphuric acid (1 part H 2 S0 4 

 7 parts H 2 0) are placed in the annular space containing 

 the platinum anode and 10 c.c. of acid (1 of acid to 19 of 

 water) put into the porous pot containing the zinc kathode. 

 The current (3 to 3j£ amps.) is then turned on and in five 

 minutes the apparatus will be full of hydrogen, and the 

 gas issuing from the drawn-out hard glass tube may then 

 be ignited. The tube is then heated for an inch from the 

 drawn-out portion by a flat Bunsen flame, a small piece 

 of platinum wire gauze being wrapped round the tube at 

 the drawn-out portion, the one end of which is heated to 

 redness by the end of the flame, the other end of the 

 gauze keeping the drawn-out portion of the tube hot to 

 within 1 Yz to 2 mm. from the wet tissue paper at which 

 the mirror is to be deposited. The suspected solution is 

 introduced into the porous pot, and washed in with 5 c.c. 

 of pure water. The test is then allowed to proceed for 35 

 minutes after the introduction of the suspected liquor, 

 the tube containing the mirror is then sealed off in 

 hydrogen, labelled and mounted for reference.* 



* In using a zinc kathode care should he taken that the strength of acid 

 does not exceed I of acid in 5 of water, otherwise the full-sized mirror is nol 

 obtained ; with a pure tin kathode this precaution is unnecessary. 



