12 GIBBS. 
Tian continued the investigations of Kernbaum and found that ultra- 
violet mercury light, principally the wave lengths 184.6, 184.8, and 185.1 us, 
and the waves 185.4, 185.7, and 186.2 uu of the aluminum spark, decompose 
water into hydrogen and hydrogen peroxide. After equilibrium is estab- 
lished, 2H.O@—H:0.+H:, pure electrolytic gas should be evolved. 
EXPERIMENTAL, 
For the detection of hydrogen peroxide I have employed the 
titanic acid®' and vanadic acid®™ tests, the Schdéenbein™ reaction, 
and Bach’s** reagent. With dilute solutions of hydrogen per- 
oxide I have found that, after the limits of the sensibility of the 
titanic and vanadic acid solutions were passed, Bach’s reagent 
continued to show positive results. 
Bach © has employed this reagent for the detection of hydrogen peroxide 
in plants. Cho” does not consider it to be reliable for the purpose, for 
he believes that other compounds in plants will produce a coloration with 
the reagent. 
It does not seem that this criticism can apply to the cases 
where I have employed the test for the reason that no other 
known reacting substances could have been present. 
Experiment I.—Three dishes containing the following mix- 
tures were covered with quartz plates, placed in the sunlight 
for one day, and then examined for hydrogen peroxide. 
I. Conductivity water 25 cubic centimeters; a sulphuric acid 5 cubic 
centimeters. 
II. Conductivity water 25 cubic centimeters. 
III. Conductivity water 25 cubic centimeters; 1 gram sodium chloride. 
The titanium reagent showed no visible reaction, while Bach’s 
reagent gave a positive but faint test with all three solutions. 
Experiment II.—The air in a tube (fig. 1), open at both 
ends and about one-third filled with conductivity water, was 
displaced with pure oxygen and the tube sealed and put in the 
" Compt. rend. Acad. sci. (1911), 152, 1012, 1483. 
% Schénn, Dingler’s Polytech. Journ. (1878), 210, 286. 
= Arnold and Mentzel, Ztschr. f. Untersuch. d. Nahrungs-u. Genuss- 
mittel (1903), 6, 305. 
" Journ. f. prakt. Chem. (1860), 79, 286. 
“ Compt. rend. Acad. sci. (1894), 119, 1218. 
The reagent consists of 0.03 gram potassium dichromate and 5 drops 
of aniline dissolved in 1 liter of water. Five cubic centimeters of the 
reagent are mixed with 5 cubic centimeters of the substance to be tested 
and 1 drop of a 5 per cent solution of oxalic acid is added. 
" Chem. Centralbl. (1896), 7, 114. 
