After this
gas is cooled, it condenses and again forms crystals which are in a
much purer condition. If necessary to further purify it, it is again
sublimed. The iron vessels in which the sublimation takes place are
lined with clay and covered with lead. The clay lining and lead
covering are necessary, for if the gas evolved during the process of
sublimation came in contact with the iron surface, the gas would be
contaminated and the iron corroded. Sublimed sal-ammoniac has a
fibrous texture and is tough and difficult to powder. It has a sharp,
salty taste and is soluble in two and a half parts of cold and in a
much smaller quantity of hot water. During the process of sublimation
the ammonia is not decomposed. But there are several ways in which the
gas may be decomposed, and a certain portion of it is decomposed in
the ordinary use of it in refrigerating machines. If electric sparks
are passed through the gas, it suffers decomposition, the nitrogen and
hydrogen then being in the condition of a simple mixture. When
decomposed in this manner, the volume of the gas is doubled and the
proportion is found to be three measures of hydrogen to one of
nitrogen, while the weight of the two constituents is in the
proportion of three parts hydrogen to fourteen of nitrogen.
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