'M-J Alhii and Crenshaw — Sulphides of Zinc, 



ougblj washed precipitates made in the above way were dried 

 and analyzed. In all of them a small excess only of mercuric 

 chloride was used, since a large excess gave finely divided pre- 

 cipitates difficult to wash. 



Found. Cal. for HgCl a .2 HgS. 



1. 2. 3. 

 Hg 81-51 81-58 



CI 9-37 fl-41 



11,0 -44 -48 



2. The reaction H 2 + HgCl., + Na„S 2 3 = 2NaCl + HgS + 

 H a S0 4 . 1-000 g. HgCl„ and 2-0 g NaCl were dissolved in water 

 and added to a solution of 0-920 g. Na 2 S 2 3 .5H„0, the total 

 volume after all was added being 150 cc . A curdy yellow-pre- 

 cipitate was obtained in the cold, probably mercuric thiosul- 

 phate, which on boiling turned black. A careful test of the 

 precipitate for chlorine revealed not more than a trace. In a 

 second experiment a solution containing ^-10 g. HgCl 2 , 2 - g. 

 NaCl and 1-000 g. K"a 2 S 2 3 .5H 2 in 150 cc water was boiled for 

 a short time and filtered. The filtrate and washings were 

 diluted to 250 cc . The resulting solution contained no mercury 

 but was strongly acid. 0-2024 g. pure dry Na 2 C0 3 required 

 119 - 4 CC of solution for neutralization, using as indicator phenol 

 phthalein at boiling temperature. Total H 2 S0 4 found = 

 0-3921. Cal. from the equation 0-3951. In a duplicate experi- 

 ment a solution identical with the first was prepared, washed 

 and filtered. The filtrate and washings were diluted to 250 ec 

 as before. 0-2029 g. pure dry Na,C0 3 required 119-5 CC solution 

 for complete neutralization. Total H 2 S0 4 found = 0-3927. 

 Cal. from the equation 0'3951. 



3. The reaction HgCl, + 4Na 2 S 2 3 = HgS + 4S + 2NaCl -f 

 3Na s S0 4 . This is the principal reaction at 100° in sealed tubes 

 when the thiosulphate is present in sufficient excess. The 

 solution is generally, however, slightly acid, and when it is 

 boiled in an open vessel considerable sulphur dioxide is evolved. 

 All the mercury is precipitated, and in two distinct layers. 

 The bottom layer, which of coi;rse, precipitated first, is bright 

 red and consists of rhe new hexagonal mercuric sulphide which 

 we will call yS'-HgS ;" :< " the upper layer consists of a mixture 

 of this form with metacinnabar, a'-HgS. The total preci- 

 pitate when mixed has a puce color almost exactly like lead 

 peroxide. It contains the a'-HgS and /3'-HgS in approxi- 

 mately equal quantities, as was estimated by matching the 

 color with various mixtures of the pure substances. 



*We will use the symbol a to designate the stable form and for mono- 

 tropic forms the symbols a\ fi' to distinguish them from enantiotropic forms, 

 for which the unaccented letters are commonly used. 



