SOLUBLE STTLPnOSALTS (3P MERCURY. 



425 



prepared for tlie purpose, and sulpluireted hydrogen was passed tln-ough 

 the sohition luilil a lavge. permanent precipitate of mercuric sulphide liad 

 formed Tlie mass was tlien filtered, and of course the filtrate represented 

 an absolutely saturated solution of mercuric sulphide in a mixture of sodic 

 sulphide and sulphydrate. A portion of this solution was analyzed. Tiie 

 remainder was treated further with hydrogen sulphide, tlie precipitation 

 being arrested before the separation of mercuric sulphide was complete, and 

 the second filtrate — representing a second saturated solution of the metallic 

 sulplnde in a mixture of alkaline sulphide and sulphydrate, but one contain- 

 ing much less mercuric sulphide than the first — was also analyzed. 



Two such analyses gave the following results per 100cm' of solution: 



Mercury, Hg. 

 Sodium, Na.. 

 Sulphur, S... 



It will readily be found that each of these analyses corresponds closely 

 to the formula HgS, 4Na^S + >(Na-S, H=S.> 



The degree of correspondence can best be seen by supposing all the 

 errors of measuring, weighing, spontaneous decomposition, and of the ana- 

 lytical methods employed to be concentrated in the determination of the 

 sulphur. Had the sulphur found been 5.9848 in A and 6.4102 in B the 

 analyses would correspond accurately to the following : 



(A) HgS + 4Na-S-j- 10.473 Na^S,H-S. 



(B) HgS -f4Na-S-f 37.757 Na-S, H-S. 



The error here supposed in the sulphur deteruiination of B is less than 

 one-fifth of 1 per cent, of the entire sulphur found, and, considering the 

 quantities actually weighed, it comes within the legitimate inaccuracies of 

 analysis. The error supposed in A is somewhat less than 1 per cent, of 

 the entire sulphur, and, when it is remembered that it really represents the 



' The mercury is of course saturated with sulphur. The sodium may also be regarded as combined 

 in the form of Na=S. Deducting the corresponding quantities of snlphnr, a remainder is If ft, whicli is 

 the sulphur combined with hydrogen in the sulphydrate Na^S, H^S. 



