Art. LIV.—On a New and Rapid Process for the Generation of Sulphuretted Hydrogen Gas for use as a Re-agent in Laboratory Operations.
[Read before the Wellington Philosophical Society, 26th August, 1871.]
Sulphuretted hydrogen gas is in such constant use in all laboratories, that I offer no excuse for submitting a new process for its generation, particularly as there appears to be a positive want for a better one than that at present in ordinary use. Indeed, owing to this want several processes have lately been published for its preparation especially having for their object a combination of evenness and constancy of delivery, but I have not learnt that the advantages promised by their several authors have been realised in actual practice. In consequence it occurred to me to try whether the reaction of metallic sulphides with zinc in acidified water, described in the third volume of our Transactions* could not be turned to account for the production of this gas.
[Footnote] * See Trans. N. Z. Lost., Vol. III., p. 222.
It will be remembered, perhaps, that in that paper I stated that an evolution 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 proper adjustment as to parts. A little hydrogen accompanies 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 use, 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 convenience 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,
[Footnote] * See Trans. N. Z. Inst., Vol. III., p. 232.
and economical one, easy of control, and capable of delivering the gas equally, continuously, and vigorously; and I am authorized to state that Dr. Hector's experience of it in the Colonial Laboratory testifies to the correctness of these assertions.