By I. TAYLOR, B.A., Science Master at Christ College, Brecon.

Hydrogen sulphide may be prepared very easily, and sufficiently pure for ordinary analytical purposes, by passing coal-gas through boiling sulphur. Coal-gas contains 40 to 50 per cent, of hydrogen, nearly the whole of which may, by means of a suitable arrangement, be converted into sulphureted hydrogen. The other constituents of coal-gas--methane, carbon monoxide, olefines, etc.--are not affected by passing through boiling sulphur, and for ordinary laboratory work their removal is quite unnecessary, as they do not in any way interfere with the precipitation of metallic sulphides.



A convenient apparatus for the preparation of hydrogen sulphide from coal-gas, such as we have at present in use in the Christ College laboratory, consists of a retort, R, in which sulphur is placed. Through the tubulure of the retort there passes a bent glass-tube, T E, perforated near the closed end, F, with a number of small holes. (The perforations are easily made by piercing the partially softened glass with a white-hot steel needle; an ordinary crotchet needle, the hook having been removed and the end sharpened, answers the purpose very well.) The end, T, of the glass tube is connected by caoutchouc tubing with the coal-gas supply, the perforated end dipping into the sulphur. The neck of the retort, inclined slightly upward to allow the condensed sulpur, as it remelts, to flow back, is connected with awash bottle, B, to which is attached the flask, F, containing the solution through which it is required to pass the hydrogen sulphide; F is connected with an aspirator, A.

About one pound of sulphur having been introduced into the retort and heated to the boiling-point, the tap of the aspirator is turned on and a current of coal-gas drawn through the boiling sulphur; the hydrogen sulphide formed is washed by the water contained in B, passes on into F, and finally into the aspirator. The speed of the current may be regulated by the tap, and as the aspirator itself acts as a receptacle for excess of gas, very little as a rule escapes into the room, and consequently unpleasant smells are avoided.

This method of preparing sulphureted hydrogen will, I think, be found useful in the laboratory. It is cleanly, much cheaper than the ordinary method, and very convenient. During laboratory work, a burner is placed under the retort and the sulphur kept hot, so that its temperature may be quickly raised to the boiling-point when the gas is required. From time to time it is necessary to replenish the retort with sulphur and to remove the condensed portions from the neck.--Chem. News.

"SETTING" OF GYPSUM.--This setting is the result of two distinct, though simultaneous, phenomena. On the one hand, portions of anhydrous calcium sulphate, when moistened with water, dissolve as they are hydrated, forming a supersaturated solution. On the other hand, this same solution deposits crystals of the hydrated sulphate, gradually augment in bulk, and unite together.--H. Le Chatellier.

[Continued from SUPPLEMENT No. 383, page 6118.]