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Art. LIII.—On the Nature of Stinkstone (Anthraconite).
[Read before the Wellington Philosophical Society, 15th February, 1893.]
It has generally, if not always, to this time been supposed that the odour that the rock known as stinkstone evolves when struck or pounded is, as it is termed, bituminous, and that the substance giving rise to this odour, or that of which it is formed, is some kind of bitumen, or a product of it.
Happening, however, to have a specimen of this stone the other day to analyse, I observed that the odour had a great resemblance to that of sulphuretted hydrogen, and upon testing for this gas in the emanations of the pounded stone I found unmistakable evidence of its presence therein.
The stone itself was of a light-grey colour, and was entirely devoid of all bituminous matter. The proportion of organic matter present was only 0.21 per cent. on the stone, and it was of the same character as the organic matter that is usually associated with limestones. Other specimens of stinkstone I analysed for this gas.
From these results I make the general statement that most, if not all, of our so-termed stinkstones contain sulphuretted hydrogen, and that it is this substance, as evolved from it when struck, that gives the odour we observe, and which has been erroneously described as bituminous.
It only remains for me now to inform you of certain interesting results which have been obtained from the experiments that I have made to discover the form in which this compound (HS) exists in the stone.
1. The stone freely evolves sulphuretted hydrogen when simply placed in hydrochloric acid.
2. The stone, ground very fine, and steeped in water for forty-eight hours, still evolved the gas very freely when afterwards placed in hydrochloric acid.
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3. The stone, ground very fine, and afterwards subjected to a red heat for two hours, gave a strong reaction of the gas when placed in hydrochloric acid.
4. When ground finely in a very small quantity of water, no sulphuretted hydrogen was found in the water, and the water appeared to be neutral.
5. The gas does not appear to be present in the vapour arising from the stone when heated to temperatures up to a red heat.
These facts appear to demonstrate that this gas (sulphuretted hydrogen) is retained in the stone in the free state, and that at a temperature of about 2,000° F. it is not expelled.
Had there been even a minute trace of it combined with a base, the water in which the stone was pounded would not have been found neutral to test-paper.
That this gas, or that small part of it not oxidized near the surfaces of the particles, adheres to the stone at a red heat is remarkable, and almost goes to prove that it is occluded, and adheres to the stone, in the same way that hydrogen is occluded and retained by red-hot palladium—that is, in some manner dependent upon the exercise of chemical force.
I have only to add here that a stone having all the qualities of stinkstone can be prepared from certain argillaceous limestones containing organic matter, by submitting them to a red heat.
The following is a statement of the composition of the stone upon which my experiments were first performed:—
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
| Carbonate of lime | 54.40 |
| Carbonate of magnesia | .93 |
| Iron protoxide | .21 |
| Sulphate of lime | Traces |
| * Siliceous matter | 42.44 |
| Organic matter | .21 |
| Water | .89 |
| † † Sulphuretted hydrogen | 0.31 |
| Loss on analysis | 0.61 |
| 100.00 |
[Footnote] * Principally clay-slate.
[Footnote] † This represents about seven volumes of the gas, and this would, but for some restraining influence, expand to more than twenty volumes of the stone when heated to a red heat. It is evident that the influence that keeps it in the finely powdered stone is of a very powerful nature.