26 Mr. Davies's Symmetrical 



of the particles of such bodies. For if we examine the solu- 

 bility of these bodies, we shall find it necessary to suppose, that 

 at no time is the simple substance itself dissolved, but always^ 

 an original and intimate compound of the substance with 

 water. These compounds are of a higher order than the 

 common hydrates, and frequently require peculiar circum- 

 stances for their formation. Silica is a good instance. Dried 

 and destitute of water it is altogether insoluble, and cannot be 

 made again to form a solid combination with water, but in a 

 state of previous and intimate combination with water it is so- 

 luble. It is evident then that the solution should be viewed 

 not as a solution of silica, but as a solution of hydrate of sili- 

 ca. The alkalies are in the same situation ; and the fact stri- 

 kingly illustrates our position, that when the alkalies dissolve 

 in alcohol they are still in the state of hydrates. The combi- 

 nation between water and lime in slaked lime is of this supe- 

 rior kind, so that lime-water may be considered not as a so- 

 lution of lime, but as a solution of hydrate of lime. The water 

 appears to be in more close union with the lime, than the water 

 of crystallization of salts to which efflorescence is confined. It 

 is therefore no objection to the theory that hydrate of lime is 

 more soluble in cold than in hot water, and yet does not efflo- 

 resce. Were the hydrate of lime to form a loose compound 

 with an additional quantity of water, like the water of crystal- 

 lization of ordinary salts, then if that hydrate did not efflo- 

 resce, the circumstance would be inimical to the theory. 



The coincidence of efflorescence with diminished solubility 

 at high temperatures, in the case of sulphate of soda, is fa- 

 vourable to the view taken of the connection between these 

 properties. If the solubility of the efflorescent salts were ex- 

 amined particularly, more of them probably would give indi- 

 cations of the same property. 



Carbonate of magnesia in crystals is very efflorescent, and 

 according to Butini * it is more soluble in cold than in hot 

 water impregnated with carbonic acid. 



V. Symmetrical Properties of Platie Triangles. By 

 T. S. Davies, Esq.qf BathA 

 [With a Plate.] 

 THHE following properties of Plane Triangles,[though inti- 

 -■■ mately connected with a very popular course of geome- 

 trical inquiry, and though far from difficult either as to in- 

 vestigation or demonstration, do not appear to have been no- 



* " Sur le Magnesie." Vide Thomson's System, under Salts of Magnesia, 

 f Communicated by the Author. 



ticed 



