IMPURITIES IN ZINC DUST 



Before using zinc dust in some experiments upon the gum 

 obtained from Japanese lac, I wished to be sure that it was free 

 from nitrogen. I therefore subjected the zinc dust to the follow- 

 ing tests, the results of which may be of interest to those who 

 frequently use it in connection with organic substances: 



When heated with potassium hydroxide it formed ammonia. 

 When heated alone it also gave off ammonia. This led to the 

 belief that nitrogen in some form had been absorbed from the 

 atmosphere, and might be removed by heat. A small quantity 

 was therefore placed in a loosely covered crucible, and strongly 

 heated for half an hour. When cold it was tested for nitrogen 

 by heating with potassium hydroxide. Its vapors rapidly changed 

 litmus paper from red to blue. Upon the suggestion of Profes- 

 sor Tschirch a sample was thoroughly washed with water acid- 

 ulated with hydrochloric acid, but this failed to completely re- 

 move the nitrogen. 



As zinc dust is manufactured by heating zinc oxide with coal, 

 it was believed that part of the nitrogen might consist of conden- 

 sation products from the coal. Therefore a sample was placed 

 in a long tube and percolated with ether. The ether when evap- 

 orated left a yellow, non-saponifiable oil, with an odor and fluor- 

 escence similar to petroleum. The oil, when heated with dry 

 potassium hydroxide, gave off alkaline vapors, and the zinc in 

 the percolator was still found to contain nitrogen. The greater 

 portion of the oil appeared to be removed with the first portion 

 of ether, but after continued percolation the ether left a residue 

 upon evaporation, and it was evident that a much larger amount 

 of ether was necessary for complete exhaustion ; therefore a small- 

 er sample, from a can of zine dust which had been in the labora- 

 tory for more than ten years, was treated with ether in the same 

 manner, and the powder tested from time to time. After using 

 a large amount of ether the zinc was practically free from nitro- 

 gen, yet by taking a large amount of the zinc and heating with 

 potassium hydroxide in a tube partially closed at the top so that 

 all of the vapors came in contact with the litmus paper, the color 

 was slightly changed, thus showing a mere trace of nitrogen. 

 This sample was then allowed to stand in an open flask for a few 

 days when it gave a decided ammonia reaction, thus showing that 

 zinc dust rapidly absorbs nitrogen from the air. 



