2 Thomson, Detection of Arsenic in Beer. 



Fig. 2 {a) shows photographic production of the mirrors in 

 three tubes, which were obtained from 50 c.c. of a solution 

 containing 5^^ of a grain per gallon of arsenic trioxide AsiOe 

 in which the naked tube was heated, whilst Fig. 2 (<^) shows 

 photographic productions of mirrors in three tubes in the 

 production of each of which 50 c.c. of the same .solution 

 were used, but where the heated portion of the tube was 

 wrapped in one layer of copper wire gauze, as recommended 

 by the Joint Committee. It will be seen, on comparing 

 these two series of tubes, that in each case more distinct 

 and reliable mirrors are obtained by heating the naked 

 tube than by heating it when wrapped in wire gauze. 



I tried to determine the temperature at which small 

 quantities of arsenic would be deposited from arseniuretted 

 hydrogen, mixed with free hydrogen by placing the tube 

 for receiving the mirror at right angles through an iron 

 tube, underneath which was a Bunsen flame which was 

 gradually raised, but I found that when heated to the 

 full safety range of my thermometer, viz.^ 393°^-> "o 

 trace of arsenic mirror was produced on the cooled 

 part of the drawn-out portion of the tube. This result 

 does not confirm the statement made in D, Mendeleeff's 

 "The Principles of Chemistry," (English edition, 1897), 

 Vol. II., p. 182, where he saj-s, in speaking of 

 arseniuretted h}'drogen — " But its presence in the most 

 " minute quantities may be easily recognised from the 

 " fact that it is easily decomposed by heat (200"'C. 

 "according to Brunn) into metallic arsenic and hydrogen." 



The gas containing arseniuretted hydrogen requires 

 to be heated to a very high temperature before all the 

 arsenic is deposited as a mirror, and it appears evident 

 that the wire gauze prevents the attainment of the 

 necessary temperature for the complete decomposition 

 of all the arseniuretted hydrogen present. 



