1872.] Mr. A. Liversidge on Supersaturated Saline Solutions. 497 



of moderate depths in the " Celtic province," recent observations having 

 merely shown that they have a somewhat greater range in depth than was 

 previously supposed. Probably Spatangus Raschi may simply be an essen- 

 tially deep-water form having its headquarters in the same region. Eight 

 species (Cidaris papillata, Echinus elegans, E. norvegicus, E. rarispina, E. 

 microstoma, Toxopneustes drobachiensis, Brissopsis lyrifera, and Tripylas 

 fragilis) are members of a fauna of intermediate depth ; and all, with the 

 doubtful exception of Echinus microstoma, have been observed in compara- 

 tively shallow water off the coasts of Scandinavia. Five species {Cidaris 

 affinis, Echinus melo, Toxopneustes brevispinosus, Psammechinus microtu- 

 berculatus, and Schizaster canaliferus) are recognized members of the Lu- 

 sitanian and Mediterranean faunse, and seven (Porocidaris purpurata, Phor- 

 mosoma placenta, Calveria hystrix, C. fenestrata, Neolampas rostellatus, 

 Pourtalesia Jeffrey si, and P.phyale) are forms which have for the first time 

 been brought to light during the late deep-sea dredging operations, whether 

 on this or on the other side of the Atlantic : there seems little doubt that 

 these must be referred to the abyssal fauna, upon whose confines we are now 

 only beginning to encroach. Three of the most remarkable generic forms, 

 Calveria, Neolampas, waft. Pourtalesia, have been found by Alexander Agassiz 

 among the results of the deep-dredging operations of Count Pourtales in 

 the Strait of Florida, showing a wide lateral distribution ; while even a 

 deeper interest attaches to the fact that while one family type, the Echi- 

 nothurida?, has been hitherto known only in a fossil state, the entire 

 group find nearer allies in the extinct faunas of the Chalk or of the earlier 

 Tertiaries than in that of the present period. 



XX. " On Supereaturated Saline Solutions." By Archibald Liver- 

 sidge, Assoc. R.S. Mines, and Scholar of Christ's College, Cam- 

 bridge. Communicated by Prof. W. H. Miller, For. Sec. R.S. 

 Received June ]3, 1872. 



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

 nomena 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 experi- 

 ments 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 Gav-Lussac, who wrote in 1819. It has since been shown 

 to be utterly untenable. 



VOL. XX. 2 o 



