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<p>The paper describes chemical tests made on several standard brands of commerical ammonia. The results of these analyses indicate that most commercial ammonias contain less than 0.1% of impurities. Five methods of the preparation of pure samples of ammonia are described and a sample was prepared which contained, as far as any known test indicated, no organic impurities, less than 1 part in 1,000,000 by volume of non-condensing gases, and less than 0.003% by weight of water.  The following physical properties of pure ammonia were determined: The /b density/ of the solid, 0.817 g./cm./sup 3/ at - 79 degrees C. and 0.836 g./cm./sup 3/ at - 185 degrees C.  The /b freezing-point/, - 77.70 degrees C., and the /b vapour pressure/ at that temperature, 45.2 mm. o
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