[ 67 ] 

 VIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from vol. xliv. p. 541.] 

 June 20, 1872. — Sir James Paget, Bart., D.C.L., Vice-President, in 



the Chair. 

 r pHE following communication was read : — 

 -*- "On Supersaturated Saline Solutions." By Archibald Liver - 

 sidge, Assoc. R.S. Mines. 



There is, perhaps, no necessity to describe in detail the ordinary 

 phenomena presented by supersaturated saline solutions, since they 

 must now be well known to all. 



The following series of experiments have chiefly been made upon 

 sodic sulphate ; but before citing them, it may, however, not be out 

 of place to briefly allude, en passant, to the conclusions drawn by 

 the numerous writers and experimenters upon this subject, since the 

 results of my own experiments are supported by the authority of 

 some of these observers and run counter to that of others. 



The theories which have been put forth are, in the main, as 

 follows : — 



a. That the crystallization of supersaturated solutions is caused by 

 purely mechanical agencies, such as agitation &c. The principal 

 supporter of this view was Gay-Lussac, who wrote in 1819. It has 

 since been shown to be utterly untenable. 



fi. That the sudden crystallization is due to some unknown cata- 

 lytic force. Advocated by Lowell in 1850, but since disproved. 



y. That it is due to the entrance of a particle of the same salt. 

 This explanation is favoured by the majority of the writers upon the 

 question, such as Ziz in 1809, Gernez in 1851, Violette in 1860, 

 Dubrunfaut in 1869, by Lecoy de Boisdandran, and others. 



£. That crystallization is due to the presence of fatty, oily, greasy, 

 or other matters in the form of thin films. This theory was pro- 

 pounded by Mr. Tomlinson in two papers* read before the Royal 

 Society, in which also it is stated that certain liquids, such as abso- 

 lute alcohol, act as nuclei in determining the solidification of such 

 solutions by separating water from the solution, whereas the thin film, 

 on the contrary, owes its activity to the greater attraction which it 

 has for the salt held in solution. 



Preparation of the Supersaturated Saline Solution* 

 A little water is placed in the flask, boiled, and sodic sulphate 

 added to the boiling liquid until it ceases to dissolve any more and 

 a deposit of the anhydrous salt begins to take place ; the solution is 

 then filtered and transferred to smaller flasks, usually of about 2 oz. 

 capacity ; these are then again boiled up after being covered with 

 a small beaker, watch-glass, or plugged with cotton-wool. By this 

 method any nuclei adhering to the watch-glass, beaker, or wool are 

 rendered inactive, even should they fall into the solution. 



The solutions are always used of such a degree of supersaturation 

 that crystals of the anhydrous salt are deposited during the boiling. 

 * Phil. Trans, vol. clviii. pt. ii. and vol. clxi. pt. i. 



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