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Book, page 110 / 445 somewhat expensive to use, but it has the advantage of not increasing the viscosity of the water; so that a frost-proof mixture of alcohol and water will flow as readily through minute tubes choked with needle- valves, or through felt and the like, or along wicks, as will plain water. For this reason, and for the practically identical one that it is quite free from dirt or insoluble matter, diluted spirit is specially suitable for the protection of the water in cyclists' acetylene lamps, [Footnote: As will appear in Chapter XIII., there is usually no holder in a vehicular acetylene lamp, all the water being employed eventually for the purpose of decomposing the carbide. This does not affect the present question. Dilute alcohol does not attack calcium carbide so energetically as pure water, because it stands midway between pure water and pure alcohol, which is inert. The attack, however, of the carbide is as complete as that of pure water, and the slower speed thereof is a manifest advantage in any holderless apparatus.] where strict economy is less important than smooth working. For domestic and larger installations it is not indicated. As between calcium chloride and glycerin there is little to choose; the former will be somewhat cheaper, but the latter will not be prohibitively expensive if the high-grade pure glycerins of the pharmacist are avoided. The following tables show the amount of each substance which must be dissolved in water to obtain a liquid of definite solidifying point. The data relating to alcohol were obtained by Pictet, and those for calcium chloride by Pickering. The latter are materially different from figures given by other investigators, and perhaps it would be safer to make due allowance for this difference. In Germany the Acetylene Association advocates a 17 per cent. solution of calcium chloride, to which Frank ascribes a specific gravity of 1.134, and a freezing-point of -8 deg. C. or 17.6 deg. F. _Freezing-Points of Dilute Alcohol._ _________________________________________________________ | | | | | Percentage of | Specific Gravity. | Freezing-point. | | Alcohol. | | | |_______________|___________________|_____________________| | | | | | | | | Degs. C. | Degs. F. | | 4.8 | 0.9916 | -2.0 | +28.4 | | 11.3 | 0.9824 | 5.0 | 23.0 | | 16.4 | 0.9761 | 7.5 | 18.5 |
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