Scientific American Supplement, No. 508, September 26, 1885 eBook

This eBook from the Gutenberg Project consists of approximately 112 pages of information about Scientific American Supplement, No. 508, September 26, 1885.
to exist throughout the whole which was previously unseen, though we have still to acknowledge that at present there is much at the root of the matter which is but imperfectly understood.  Still Dr. Guthrie proves a relationship to exist between the several facts we have previously mentioned, and also between a number of other phenomena which at first sight appear to be equally isolated and unexpected, and we are asked to regard them all as examples of what he has called “eutexia.”

We may define a eutectic substance as a body composed of two or more constituents, which constituents are in such proportion to one another as to give to the resultant compound body a minimum temperature of liquefaction—­that is, a lower temperature of liquefaction than that given by any other proportion.[2] It will be seen at once by this definition that the temperature of liquefaction of a eutectic substance is lower than the temperature of liquefaction of either or any of the constituents of the mixture.  And, further, it is plain that those substances only can be eutectic which we can obtain both as liquid and solid, and hence the property of eutexia is closely connected with solution.

   [Footnote 2:  Guthrie, Phil.  Mag. [5], xvii., p. 462.]

Following in the natural divisions adopted by Dr. Guthrie, we may consider eutexia in three aspects: 

I. CRYOHYDRATES.

If a dilute aqueous saline solution be taken at ordinary temperatures, and then slowly cooled to some point below zero on the Centigrade scale, the following series of changes will in general be observed:  On reaching a point below zero, the position of which is dependent upon the nature of the salt and the amount of dilution, it will be found that ice is formed; this will float upon the surface of the solution, and may be readily removed.  If the ice so removed be afterward pressed, or carefully drained, it will be found to consist of nearly pure water, the liquid draining away being a strong saline solution which had become mechanically entangled among the crystals of ice during solidification.  If we further cool the brine which remains, we notice a tolerably uniform fall of temperature with accompanying formation of ice.  But at length a point is reached at which the temperature ceases to fall until the whole of the remaining mother-liquor has solidified, with the production of a compound called a cryohydrate,[3] which possesses physical properties different from those of either the ice or the salt from which it is formed.

   [Footnote 3:  Guthrie, Phil.  Mag., 4th Series, xlix., pp. 1,
   206, 266; 5th Series, i., pp. 49, 354, 446, vi., p. 35.]

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