﻿322 Transactions — Chemistry. 



It will be remembered, perhaps, tbat in that paper I stated that an evolu- 

 tion of sulphuretted hydrogen occurred under the above circumstances, the 

 gas being thrown off from the surface of the sulphide used, while the zinc was 

 oxidized and the sulphur of the sulphide hydrized, a true voltaic pair forming, 

 as further demonstrated in an ensuing article.* 



This reaction, therefore, I applied in the following modified manner, and 

 found it to answer so well that I am induced to make the process public for 

 the benefit of practical chemists : — 



Fragments of galena and granulated zinc, in proportions of about 1 to 1, 

 are well mixed and put into a small apparatus of the kind generally in use for 

 the preparation of this gas, and hydrochloric acid diluted with water (1 to 20 

 or so) poured upon them. Sulphuretted hydrogen is instantly given off, and 

 its evolution is found to proceed energetically, regularly, and continuously for 

 a great length of time — a length proportionate to that of the quantity of 

 material used and its pi'oper adjustment as to parts. A little hydrogen accom- 

 panies the gas named, and traces of hydrochloric acid. The acid is, however, 

 easily removed, by allowing it to pass through a little carbonate of lime before 

 nse, while the presence of hydrogen can have no bad effect for all ordinary 

 purposes. 



After a sufficiency of the gas has been used it is best, in ordinary cases, 

 simply to wash the galena and zinc with water, when the apparatus is ready 

 for further use at a moment's notice ; but when quantities are required in rapid 

 succession a form of apparatus may be used which allows the separation of the 

 acid liquid from the undecomposed substances, within itself, when the delivery 

 tube is closed. But a still more excellent method may be had recourse to in 

 such cases, and this is to make the necessary electric contact of the zinc with 

 the sulphide dependent upon the juxtaposition of moveable wires carried 

 outside the apparatus. For this it is only necessary to use them in mass 

 instead of in fragments, connecting them electrically by means of wires, which 

 are passed through the cork of the apparatus, and which are only allowed 

 contact with each other by means of proper connecting screws. 



If care is taken to keep the zinc and sulphide from direct contact, the 

 evolution of gas instantly ceases on disconnecting the wires, and commences 

 on making the connection. 



For this last method it is necessary to amalgamate the zinc. I should state 

 that any sulphide which is an electrical conductor may be substituted for 

 galena, such as sulphide of iron or copper, but for cheapness and general con- 

 venience I recommend galena. 



Having used this method during the last six months a great number of 

 times, I have no hesitation in recommending it as a most simple, expeditious, 



*See Trans. N. Z. Inst., Vol. III., p. 232. 



