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I. II, Illustrative of Mr. Piazzi Smyth's Paper on Carbon and Hydro-
carbon in the Modern Spectroscope.
III. IV. V. VI. Illustrative of Mr. J. Rand Capron's Paper on the Com-
parison of some Tube and other Spectra with the Spectrum of
VII. Illustrative of Dr. H. F. Weber's Paper on the Specific Heat of the
Elements Carbon, Boron, and Silicon.
VIII. Illustrative of Prof. G. C. Foster's Paper on Graphical Methods of
solving certain simple Electrical Problems.
the Flow of Electricity in a uniform plane conducting Surface.
1. On Salt Solutions and Attached Water.
By FREDERICK GUTHRIE*,
London by Dr. J. Rae, the arctic explorer, on the
Chloride of Sodium.
* Read before the Physical Society, November 7, 1874. Communicated
† Proc. Phys. Soc. May 9, 1874. Phil. Mag. July 1874, p. 56.
of any metal having an atomic weight differing by more than 5 from that of sodium could be present, supposing it to be a chloride. On converting the chloride into a sulphate an equally accordant result was got. This convinced me that I had a perfectly pure substance.
§ 3. Preparation of the Brine.—The clearest lumps of the rock-salt were washed in common and then in distilled water. With these a large beaker was filled. Distilled water was poured on so as to fill the beaker about two thirds. If part of the salt is thus always above the surface of the brine, the latter appears to be saturated in twenty-four hours. After forty-eight hours the brine was poured into another beaker and allowed to stand until crystals began to be formed. It was then transferred to a stoppered bottle and was ready for use. Although Regnault and others have shown that for temperatures above 0° C. the solubility of chloride of sodium in water is constant, yet the precaution was taken of suspending a muslin bag containing some crystals of salt from a string passing through the cork of the bottle so that the crystals touched the surface of the brine. By this means the perfect saturation of the brine was assured. At 18° C. this solution contained 26•2724 per cent. of salt. The solution was weighed in a long-necked flask, and was evaporated to dryness and heated to about 300° C.
The following numbers show the results obtained by some other experimenters :
spec. grav. Kopp
Sat. at 25 C. contains 26.32
1:2046 F. G.
1•2011 The above specific gravities are referred to water at the same temperature as the brine, as far as my own experiments are concerned.
4. Cold produced on mixing saturated Brine with Water.-To examine this point, a series of covered beaker-glasses containing known weights of water, and a similar series containing saturated brine, were placed side by side in a tin tray containing water and resting on flannel. The whole arrangement was covered with flannel and allowed to stand over night. In the morning the temperature of eight or ten was found to be exactly 21° C. The liquids were prepared by measuring out from a burette in proportions that, taking 1.1997 as the specific gravity of the brine, the ratios by weight were as in columns 3 and 4 (Table 1.). The experiments were performed by taking out a water-beaker, rapidly drying its outside, pouring in the brine, stirring with the thermometer, and at once reading.
TABLE I. Cold produced on mixing saturated Brine with various propor
tions of Water by weight. Initial temperature 21° C.
The greatest depression of temperature accordingly in the range of ratio between 84 and 90 of water and 16 and 10 of salt, and the greatest depression of temperature to be got by mixing saturated brine with water, is under no circumstance quite loc.
$ 5. If now anhydrous salt on dissolving in water absorbs heat only by reason of its conversion into a liquid, and if no hydrate of salt exists at the ordinary temperature above 0° €., no such absorption of heat as we have seen to occur could ensue on mixing brine and water. Two series of experiments are therefore at once demanded :—the first to see wbat proportion must exist between anhydrous salt and water to absorb the most heat; the second to see if at any ratio between salt and water an abnormal change of density takes place.
§ 6. Cold produced on mixing NaCl with Water.—A quantity of rock-salt having been finely powdered, was passed through muslin so as to be quite mealy. Various quantities of distilled water were weighed into beakers, and various quantities of the rock-salt were thrown in under constant stirring. The abasement of temperature being noted gave the results of Table II. The temperature of the salt was about 2° C. above that of the water.