40 Historical Sketch of Improvements in [July, 



was tenuiaated by a dihedral summit formed by two laces pro- 

 ceeding from the narrow liaces of the prism, and meeting at an 

 angle of 130°. 1 fomid them composed of 



4 atoms acetic acid = 21*85 



5 atoms oxide of lead = 60*00 



19 atoms water = 18* 15 



100-00 



So that it is a subacetate with the addition of one-fourtli of aa 

 atom of oxide of lead over and above what exists in common 

 sugar of lead. This salt has been occasionally formed in other 

 manufactories. 1 have a very fine specimen of it from Mr. 

 Ramsay, of Glasgow. 



10. Suits of Mercury. — Mr, Donovan's paper has made us 

 much better acquainted with several of the salts of mercury than 

 we were before. 



(1.) JSiirate vf Mercury. — When mercury is dissolved in pure 

 nitric acid, whether with or without the assistance of heat, a 

 number of crystals speedily make their appearance, which Mr. 

 Donovan has shown to be pure protonitrate of mercury. This 

 salt is white and opaque. If exposed to the air, it becomes 

 yellow, by losing a portion of its acid. It does not dissolve in 

 water, unless the liquid be acidulated with nitric acid. When 

 this salt is digested in a sufficient quantity of water, it is con- 

 verted into a blue-grey matter, which consists of a subnitrate of 

 mercury. 



The pernitrate of mercury does not crystallize, and, if evapo- 

 rated to dryness, is deliquescent. This salt remains behind after 

 the protonitrate of mercury has separated in crystals from the 

 solution of mercury in nitric acid. 



(2.) Sulphate of Mercury. — When sulphuric acid is heated 

 over mercury so gently as merely to efi'ervesce, a white salt is 

 speedily deposited, which is a protosulphate of mercury. It 

 dissolves very sparingly in sulphuric acid, and is decomposed by 

 water. There is another variety of this salt ; namely, the sub- 

 protosulphate, which may be obtained by mixing together the 

 solutions of protonitrate of mercury and sulphate of soda. The 

 precipitate which falls is ^\hite, and consists of subprotosulphate 

 of mercury. When protoxide of mercuiy and sulphuric acid (of 

 the specific gravity 1-09) are triturated together, the colour of 

 the oxide changes to grey, but none of it dissolves. This like- 

 wise (when well edulcorated) is a subprotosulphate of mercury. 



When sulphuric acid is violently boiled on any quantity of 

 mercury, the metal is first brought to the state of black oxide ; 

 but bv continuing the heat, it is converted into peroxide. If a 

 mixture of three parts strong acid and two parts mercury by 

 weight be boiled together for a sufficient time, the whole is 

 canvei'ted into persulphate of mercury. This salt, like the other, 



