MERCURY PERCHLORATES. 79 



undissolved a white basic salt. This, again, is decomposed by water, 

 which leaves behind impure mercuric oxide. Alcohol added to an 

 aqueous solution of mercuric perchlorate gives an orange precipitate, 

 mainly mercuric oxide. As to the formation of mercurous oxide or 

 mercurous salt, which, is mentioned as taking place on evaporating 

 the mother-liquor, that happens to a small extent only, and because 

 mercuric salts are reduced by hot alcohol. 



Of the composition of mercuric perchlorate all that is known is 

 that, on the authority of Serullas, it is expressed by Hg(C10 4 ) 2 ; it 

 passes for an anhydrous salt (Roscoe and Schorlemmer's Treatise ; 

 Muir and Morley's Watts 1 Dictionary, etc.). It proves, however, to be 

 a hydrated salt, with as much as six mois, of water, which, though it 

 can be readily got from the salt by heat, cannot well be directly 

 estimated, since perchloric acid is liberated along with it from the 

 first. The composition of the salt was determined by precipitating 

 the mercury as sulphide and obtaining the perchloric acid from the 

 filtrate as its potassium salt, with the precautions given in Roscoe's 

 paper. The formation of a very little sulphuric acid in removing the 

 excess of hydrogen sulphide cannot be avoided, and this comes out in 

 the potassium perchlorate and, small as it is, has to be taken account 

 of. In the second of the analyses, the results of which are here given, 

 the mercury was precipitated by gaseous hydrogen sulphide without 

 addition of acid; in the first, it was precipitated by adding at once 

 excess of hydrogen-sulphide-water, and then a cubic centimeter of 

 dilute sulphuric acid to coagulate the mercury sulphide. The total 

 sulphuric acid having been determined, the corresponding quantity of 

 potassium sulphate was deducted from that of the potassium perchlorate 

 and sulphate together. In consequence of what has just been stated, 

 this procedure introduced no complication, while the use of hydro- 

 chloric acid was precluded, as interfering with the determination of 



