Chemistry / by George Wilson.

  • George Wilson
Date:
1859
Catalogue details

Licence: Public Domain Mark

Credit: Chemistry / by George Wilson. Source: Wellcome Collection.

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    solid bodies. Thus, if we compare the weight of a certain volume of water with exactly the same bulk of iron, we shall find that the iron is nearly 8 times heavier than its own volume of water, whilst platina is 21J times denser than an equal bulk of that liquid. We express this numerically thus:— Water, sp. gr. (specific gravity) 1' or 1000 Iron, sp. gr. 8- or 8000 Platina, sp. gr. 21-5 or 21,500 In other words, these numbers express this fact, that a space which, when quite filled at a certain temperature and pressure of the atmosphere, contained 1000 grains of water, would, at the same temperature and pressure, hold 8000 of iron, and 21,500 of platina. 35. Gases are so much lighter than water—air, for ex- ample, being 815 times lighter—that it would be found ex- tremely inconvenient to make water the standard of specific gravity for elastic fluids. Air, accordingly, is substituted for it, and the specific gravity of air is called 1 or 1000. Thus the gases carbonic acid and chlorine are heavier than air; nitrogen, on the other hand, is lighter. The exact numbers denoting their specific gravity are the following :— Air, 1000 Nitrogen, 972 Carbonic Acid, 1524 Chlorine, 2440 These numbers, like those already given, express the fact, that a vessel which, when full of air at a certain temperature and pressure, contains a thousand grains of that gas, will, at the same temperature and pressure, though filled quite as full, contain only 972 grains of nitrogen; whilst, when filled no fuller by the heavier gases, it will contain 1529 grains of car- bonic acid, and 2440 of chlorine. The containing vessel having been the same in all the trials, and filled each time, there cannot be any difference in the volumes of the gases taken. The difference in weight is determined solely by the fact, that within exactly equal spaces, different bodies contain unlike quantities of ponderable matter. 36. Many precautions and niceties are necessary in the practical determination of specific gravity. The methods and minutiae, which require attention, must be learned from works on natural philosophy. No character of a body, however, is more frequently referred to by the chemist than its specific gravity; hence our detailed discussion of it. The specific
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