Cadmium, and Mercury. 353 



therefore, not be necessary to describe the experiments in 

 detail. Two other experiments of a negative nature may also 

 be mentioned here. The behavior of metallic zinc in saturated 

 sulphurous acid solution gave only amorphous sulphide in 

 rather large grains — of refractivity 2'2 — 2 - 3. On account of 

 the weak nature of this acid it was thought sphalerite might 

 possibly be formed. The action of powdered marcasite on 

 zinc chloride in an atmosphere of carbon dioxide gave no 

 sulphide of zinc. 



Formation of Sphalerite by precipitation with alkali sulpirides. 



The precipitate from zinc salts by alkali sulphides in the 

 cold, or under ordinary conditions at a boiling temperature, 

 shows no indications of crystallinity. However, when pretty 

 concentrated solutions of the soluble sulphides act on amor- 

 phous zinc sulphide at higher temperatures, sphalerite is 

 obtained. As previously stated, experiments with concentrated 

 alkaline solutions gave much trouble. The glass tubes were so 

 badly attacked that the products obtained in them were quite 

 impure, greatly increasing the difficulties of microscopic 

 analysis, while at 300° the tubes were sometimes eaten entirely 

 through. The difficulty was finally overcome by putting the 

 solutions into platinum tubes which were then set inside of 

 glass tubes, the latter being afterwards sealed. Satisfactory 

 platinum tubes which are not so expensive as to be prohibitive 

 may be fashioned from foil by the use of the oxyhydrogen 

 blowpipe. Ours had a diameter of about 15 mm and a total 

 capacity of about 40 cc . 



In our first successful experiment amorphous zinc sulphide 

 was put into a tube of Jena combustion glass* with sodium 

 sulphide of about 20 per cent concentration ; the tube and its con- 

 tents were heated 3 days in a steel bomb at 350°. Small though 

 good crystals of sphalerite, both octahedrons and tetra- 

 hedrons, were obtained. Again, amorphous zinc sulphide was 

 heated in a platinum tube sealed inside a glass tube, as 

 described above, with potassium sulphide of about 35 per cent 

 at 200° for 11 days. Minute tetrahedrons of sphalerite were 

 obtained. A solution of 10 per cent potassium sulphide heated 

 with amorphous zinc sulphide in a similar manner at 200° for 

 two monthsf gave a product which was entirely crystallized in 

 minute isotropic crystals with evident faces but rather rounded 

 edges. A second experiment with 10 per cent sodium sulphide 

 lasting six weeks at 100° failed to yield any crystals. Thus we 

 find, as we should expect, that the lower the temperature and the 

 more dilute the reagent the longer is the time required to 



*Out of a large number of experiments with glass tubes, this was the 

 only one in which the product could be recovered. 



\ By mistake the temperature was dropped to 100° for a part of the 

 period. 



