50 On some of the Combinations of Mercury. 



end changes tlieir form into that of minute hexagons. On the 

 other hand it sometimes happens, that, under similar circum- 

 stances, hexagonal pronitrate is formed, alter which the super- 

 abundant acid in them is abstracted by the solution, and the 

 chrystals are changed into acicular prisms. 



The rhombic pronitrate is insoluble in cold water, but when 

 acted upon by boiling water is decomposed, the water dis- 

 solving a portion of protoxide in combination with an excess of 

 acid, and a portion of yellow insoluble pronitrate being pre- 

 cipitated. The rhombic pronitrate is soluble in a solutiou of 

 hexagonal or acicular pronitrate, a property which enables us 

 to obtain it rapidly. For this purpose the compound obtained 

 by triturating peroxide of mercury, metallic mercury, und 

 nitric acid together, in the proportions already mentioned, is 

 exposed to a heated solniion of pronitrate when a fourteenth 

 part of the compound is dissolved, and is deposited in the form 

 of rhombic chrystals upon cooling. By repeating this process 

 any quantity of the chrystals may be obtained. 



All the pronitrates ate decomposed by ammonia, which 

 throws down a black precipitate from each of them. This 

 precipitate when washed with boiling water becomes blue, and 

 this blue powder when exposed to heat is again decomposed, 

 metallic mercury being evolved, and being evaporated, a reddish 

 powder remains. This red powder when further urged with 

 heat, diminishes in quantity, and a small quantity of while 

 powder is left. From these results I am led to conclude, that 

 this blue precipitate is net a pure protoxide of mercury, but 

 protoxide containing a portion of the alkali. 



Potash added to hexagonal or acicular pronitrate, attacts 

 first a portion of acid, and causes the formation of a white 

 precipitate; an additional quantity changes this to yellow; and 

 a still larger quantity changes it to blue. These successive 

 changes are no doubt owing to the gradual abstraction of acid 

 from the oxide of mercury, and consequent formation, first, of 

 the white pronitrate, similar in composition to rhombic proni- 

 trate, and lastly of a compound containing no acid. This com- 

 pound when washed with water is similar in appearance to the 

 compound obtained from the action of ammonia, and is proba- 

 bly protoxide of mercury in combination with a portion of 

 potash. Whether they shall be found to be pure protoxide, or 

 protoxide in combination with an alkali, this and the preceding 

 substance may, 1 would suggest, be advantageously employed 

 in any case where a mild preparation of mercury is wanted. 



Permtrate of mercury when exposed to a temperature of 

 about G00°, is converted into a red compound which has ro- 

 ceived the name of red precipitate, and of nitroxidc of mercury. 



