81 



40° Fahrenheit. It is the only known crystaUizable hydrate of sul- 

 phuric acid, and may be represented thus : — 



SHH, 

 which may be compared with the formula for sulphate of zinc, with- 

 out water of crystallization — 



szii. 



This second atom of water present in hydrated sulphuric acid is re- 

 placeable by sulphate of potash, a salt ; and the bisulphate of potash 

 results from the substitution. But the first atom of water in the 

 acid hydrate can be replaced only by an alkali or true base. The 

 function of the first atom is basic, but a new term is required to dis- 

 tinguish the function of the second atom. The application of the 

 epithet saline to that atom of water may perhaps be pernutted to in- 

 dicate that it stands in the place of a salt. The hydrate of sulphuric 

 acid in question contains, therefore, an atom of basic, and an atoni ot 

 saline water. It is » a sulphate of water with saline water, as hy- 

 drous sulphate of zinc is " a sulphate of zinc with saline water. 

 The bisulphate of potash is also « a sulphate of water with sulphate 

 of potash," and corresponds with the sulphate of zinc and potash, 

 which last is " a sulphate of zinc with sulphate of potash." 



Sulphuric acid of sp. gr. 1-78 is therefore the primary salt, and 

 gives the character of the sulphates. This acid hydi-ate corresponds 

 closely with the sulphate of magnesia, which is the reason they do 

 not combine together. Hence there are no acid or supersulphates of 



magnesia, zinc, &c. 



Of the two atoms which hydrated sulphate of lime, or gypsum, 

 contains, one is expelled at 212= in vacuo; and the other, which is 

 the saline atom is not retained at a higher temperature than 300 . 

 Hence sulphate of lime has less disposition to form double sulphates 

 than the sulphate of magnesia, &c. 



Professor Forbes announced the results of an Experimental investi- 

 gation into the Polarization and Refraction of Heat. The reading 

 of the paper on this subject was commenced. 



