MERCURY PERCHLORATES. SI 



been heated to form it. Therefore, water dissolves out normal mercuric 

 pet-chlorate, and, since 12'90 is almost exactly the third part of 31)*:25, 

 the percentage amount of perchlorate radical in the original salt, the 

 change effected by heat may be formulated thus:— 



3[Hg(C10 4 ) S5 6H 2 0]=0 2 Hg 3 (C10 4 ) 2 + 4HC10 4 +l6H 2 0; 



2 Hg 3 (C10 4 ) 2 expressing the composition of the oxymercuric per- 

 chlorate. 



Mercurous pereli lorate. 



Mercurous perchlorate can be very quickly prepared by violently 

 shaking a solution of mercuric perchlorate with mercury for a few 

 minutes, after which nothing but the mercurous salt will be found in 

 the solution. Such a solution cannot be left for days, or be heated 

 long on a water-bath, without letting fall some basic salt, but a con- 

 centrated solution can be evaporated in a vacuum-desiccator fast 

 enough to avoid this. With rapid evaporation, the salt is obtained in 

 fine needles, as described by Serullas. These needles are flat and, with 

 slower evaporation, develope into flattened prisms or plates of con- 

 siderable size. 



The salt is exceedingly soluble in water, by which, in large 

 quantity, it is often decomposed. It causes a sensible fall in tem- 

 perature in dissolving. Its solution is neutral to litmus. Serullas 

 found the salt to be unchanged by exposure to air, and must, therefore, 

 have been working in very dry weather. For it is, as Roscoe describes 

 it, very deliquescent, though less so than the mercuric salt. Ac- 

 cording to this chemist, it does not lose water, either at 100° or in 

 vacuo over sulphuric acid. This is not really the case, but the loss of 

 weight is slow enough in either case to be easily overlooked. In 

 about two weeks in a vacuum-desiccator, the loss reaches nearly six 



