48 On some of the Combination of Mercury. 



where hiilierto the Company have only succeeded in procuring 

 from Brazil the wild kind, producing the Sylvestre cochineal, 

 which is of very inferior value." — Kir by § Spc.nce's Introduction 

 to Entomology , four th edition, vol. I. p. 318 to 322. 



C. F. H. von Ludwio, Phil; Dr. 



Member of the S. A. Institution. 



On some of the Combinations of Mercury. By Mr. Reid. 



[Head at llie South African Iastitution.J 



Mercury combines in two proportions with oxygen : the 

 peroxide, that is the oxide containing the maximum of oxygen, 

 being of a red colour ; the protoxide or oxide containing the 

 minimum of oxygen being blue. Each of these oxides may be 

 combined with nitric acid, forming metallic salts. 



Pernitrate of mercury, or nitric ncid in combination with 

 peroxide of mercury, is formed by the action of concentrated 

 Ditric acid, but always with nn intermixture of pronitrate or acid„ 

 in combination with protoxide of mercury. In order to obtain 

 the pernitrate, pure peroxide of mercury is dissolved in nitric 

 acid, the solution by evaporation yielding small ncicular 

 chrystals. It is extremely soluble in water, is very acrid and 

 tinges the skin of a brown colour. The addition of water de- 

 composes it ; one part remaining in solution contains peroxide 

 of mercury with an excess of ncid, a precipitate being formed 

 which consists of the same oxide with a diminished proportion 

 of acid. The solution when again evaporated yields acicular 

 chrystals as before, the excess of acid remaining in solution. 

 When mercury is added to this solution it attracts a proportion 

 of the oxygen from the peroxide, and both are converted into 

 protoxide, which, uniting- with the nitric acid, a pronitrate of 

 mercury is formed instead of the pernitrate. 



When mercury is exposed to the action of nitric acid diluted 

 with two parts of water, it is slowly dissolved and pronitrate of 

 mercury formed. The combination ceases before the whole of 

 the acid is acted upon, but when heat is applied it recom- 

 mences, and by gradually increasing the temperature when the 

 action stops, the whole of the acid may be made to combine 

 with the mercury forming pronitrate. In this case, however, 

 the combination is not limited to one proportion of acid and 

 protoxide. If the combination is stopped before the whole of 

 the acid is taken up, it appears in the form of hexagons or 

 hexagonal plates. If it is continued till no acid remains, the 

 form of the chrystals is that of acicular prisms. When boiling 



