:>T4 Allen and Crenshaw — Sulphides of Zinc, 



portionslarge enough lor a specific gravity determination, we used 

 the following solution: 6 ff. HgCl, :60ff. NaCl ; 12<>-. Na,K () . 

 511 ,(> in 41. of water. L0 co '60 per cent sulphuric acid was added 

 and the solution boiled till precipitation was complete. More 

 than a proportional quantity of acid was thus required for the 

 larger volume of solution. The precipitate, after thorough 

 washing, was dried with alcohol and ether ; then the sulphur 

 was removed by repeated digestion with carbon disulphide, 

 washed with ether, and dried by heating in vacuo to 250°. It 

 contained only a trace of occluded salt. A weighed portion 

 dissolved in aqua regia and changed to chloride with excess of 

 hydrochloric acid was precipitated with hydrogen sulphide. 

 The filtrate was evaporated to dryness and finally heated to 

 redness in a tarred platinum dish and weighed. Three-tenths 

 of a milligram of sodium sulphate in one gram substance 

 = 0"03 per cent was thus obtained. Of course this does not 

 prove the original form of the sodium to have been sulphate, 

 though it probably was. The sulphide was tested for water by 

 heating in an atmosphere of carbon dioxide, till it was largely 

 volatilized, the water being absorbed by calcium chloride. Of 

 course precautions were taken to guard against driving the 

 sulphide vapor over into the absorption tube, and when the 

 apparatus was cold, the carbon dioxide was removed by dry air. 

 No water was found. Under the microscope the product was 

 apparently all crystalline, though it was impossible to say that 

 there was no intermixture of amorphous sulphide. 



The slow precipitation of mercuric sulphate or chloride in 

 strongly acid solution by hydrogen sulphide was also tried for 

 the preparation of this form. The device referred to on p. 355 

 was used for the purpose. The products obtained in this way 

 showed no crystal faces, and being opaque it was impossible to 

 say whether they were crystalline or not. Similar products 

 were also obtained by the action of sulphur and sulphuric acid 

 on metallic mercury in closed tubes containing an atmosphere 

 of hydrogen sulphide. At high temperatures, 200° and 300°, 

 respectively, some cinnabar was obtained by both the last two 

 methods. 



Properties of a'-HgS. The opacity of the black mercuric 

 sulphide made optical tests on it impossible. The attempt to 

 prepare measurable crystals of it was futile and therefore our 

 product could not be certainly identified with metacinnabar. 

 The following facts, however, make the identity highly prob- 

 able. Both minerals are entirely black when pure, even in a 

 powdered condition. Natural metacinnabar is regarded as 

 tisometric ; the laboratory product was obtained from thiosul- 

 phate solutions in the form of bars crossed at right angles like 

 the principal axes of a cube, suggesting skeleton crystals of the 



