OF ARTS AND SCIENCES. 113 



VIII. 



ON A NEW MODE OF MANIPULATING HYDRIC 



SULPHIDE. 



By Josiah p. Cooke, Jr., 



Erving Prqfessor qf Chemistry and Mineralogy in Harvard College. 

 Presented May 30th, 1876. 



In chemical laboratories, where instruction in qualitative analysis is 

 given to large numbers on the class system, the use of hydric sulphide 

 gas as a reagent is attended with grave inconveniences. These evils 

 can in great measure be avoided by substituting for the gas a solution 

 of the reagent in water, saturated at the ordinary temperature and 

 pressure of the air ; when, as is well known, one volume of water 

 dissolves about 3.4 volumes of the gas (measured at 15° C. and 76 

 cm.). Such a solution was for a long time used in the laboratory of 

 Harvard College. It was prepared in a long series of two litre bottles 

 connected by glass tubes in the usual way, and the solution was kept 

 in the laboratory in a large tubulated glass flask, from which it was 

 drawn by the students, as occasion required. This solution answers 

 almost every purpose for which the reagent is used in the ordinary 

 course of qualitative analysis, and the few conditions under which it 

 does not give satisfactory results can be easily avoided. Moreover, in 

 ease of application and promptness of effect it has all the advantages 

 of a liquid reagent ; and the only inconvenience its use involves is an 

 occasional evaporation of a solution, which the dilution by the reagent 

 may render necessary. Of course a solution of hydric sulphide is 

 liable to oxidation, and soon becomes turbid in contact with the air ; 

 but this change can be easily avoided by fitting to the neck of the 

 flask (in which the solution is kept), by means of a rubber stopper, a 

 glass tube dipping under the liquid, and connecting this tube with one 

 of the vents of illuminating gas in the laboratory. 



For quantitative work, and for the preparation of chemical products, 

 when considerable quantities of metallic sulphides must be precipitated, 

 a solution of hydric sulphide, saturated under the ordinary pressure of 



VOL. XII. (N. S. IV.) 8 



