Volume 2

Modern chemistry / by William Ramsay.

  • William Ramsay
Date:
1900
Catalogue details

Licence: In copyright

Credit: Modern chemistry / by William Ramsay. Source: Wellcome Collection.

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    The Analysis of the Atmosphere is, however, always performed by chemical means, for the difference in physical properties of its constituents is not sufficiently marked to allow of their being utilised for purposes of separation. Many common elements unite easily with oxygen to form non-volatile compounds, when they are heated in air. One of the most convenient for this purpose is metallic copper. By passing a known volume of air over copper turnings, contained in a counter- poised tube of hard glass, and heated to redness, the oxygen of the air is removed, for it combines with the copper to form non-volatile black oxide of copper. The in- crease in weight of this tube gives the weight of the oxygen in the measured volume of air. But it is customary to analyse air volumetrically by absorbing the oxygen from a known volume by means of burning phosphorus, <?r of a solution of potassium pyrogallate : the remainder consists of a mixture of nitrogen, argon and its congeners. The separation of these gases from each other is described in the next paragraph. Reference has already been made in Part I. to the different processes which may be used for the isolation of elements from their compounds. But there exists a group of elements, that of which the first member is helium, which form no com- pounds, and which therefore are found only in a free state. It is, therefore, convenient to begin with these. The HELIUM Group. —These elements are all gases at the ordinary temperature of the atmosphere, and they are consequently all to be found in atmospheric air. They are colourless, even in the liquid condition, and are devoid of smell and taste. They are very sparingly soluble in water; for example, ioo volumes of water dissolve only 4.1 volumes of argon at 150. Their preparation consists, first, in the separation of the other constituents of air from them, and, second, in their separation from each other. Air, which is a mixture, and not a compound, of nitro- gen, oxygen, carbon dioxide, ammonia, water-vappur, and the gases of the helium group, is a supporter of combustion,
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