202 Conductivity of Aqueous Solutions. Part VII. 



within 0.1 per cent. Samples of the water, after being heated to 218 or 

 306, showed an increased conductance at 18, and were not changed by 

 further heating, indicating the presence of a small amount of some organic 

 substance, which was decomposed or oxidized at the high temperatures. 



If originally present in the strong ammonium hydroxide solution from 

 which the diluter solution was made, carbon dioxide of course would have 

 the same effect as if present in the water, in giving too high a value. In 

 fact, practically any imaginable impurity in the strong solution would have 

 the effect of increasing the conductance, so that the lowest value obtained 

 should be considered the most accurate one. 



In the first experiments made with ammonium hydroxide, as will be 

 shown later in the data, the specific conductance had always decreased 

 about 1.9 per cent at 18, after the heating to 218. The first three experi- 

 ments were made without exhausting the air from the bomb ; in the third, 

 the bomb was twice reheated, causing further diminutions of 0.6 per cent 

 and 0.25 per cent. In the fourth experiment the air was exhausted down 

 to 4 cm. pressure, which reduced the decrease after the heating to 1.3 per 

 cent. In all cases there was a slight suction when the bomb was opened. 



These facts show that some change occurred at the higher temperature 

 which caused a permanent decrease in the conductance. Any contamina- 

 tion would be almost certain to increase it. There was no leak, for the 

 conductance at the upper electrode remained perfectly constant. There was 

 no escape of ammonia through the platinum, for the effect did not con- 

 tinue to an appreciable extent after the second heating. Adsorption by 

 the platinum is not likely, for the effect was almost exactly the same in 

 each run. The most probable explanation is that the oxygen left in the 

 vapor space, in solution, and on the platinum surface, oxidized part of the 

 ammonia to nitrogen and water; this would account also for the decrease 

 of pressure within the bomb, as is evident from the following equation : 

 4NH 4 OH -f30 2 = 2N 2 + 10 H 2 0, which shows a decrease of one mol 

 of gaseous substances. 



The oxidation of ammonia in the presence of platinum black seems to be 

 a well established phenomenon. Henry* observed that platinum sponge 

 caused slow oxidation in a mixture of ammonia and oxygen at 193. 

 Mond, Ramsey, and Shieldsf removed oxygen from spongy platinum by 

 this reaction. VondracekJ found that an 0.087 normal solution is oxidized 

 by platinum sponge at ordinary temperatures ; boiling solutions of ammo- 

 nium salts are also oxidized by it. Platinum containing no oxygen had a 

 slight reducing action. 



*Ann. Philos., 25, 424 (1825). 

 fZ. phys. Chem., 25, 657 (1897). 

 %Z. anorg. Chem., 39, 24 (1904). 



