Thomas Thomson

XXII. On Asbestus, Chlorite, and Talc

Notwithstanding the great progress which Mineralogy has made of late years, towards the division of minerals into accurate and well defined species, there are several groups which occur in the oldest mineral systems extant, and which have continued to the present time with very little alteration or improvement. I allude to the minerals classed under the names of Asbestus, Chlorite, and Talc. As these minerals, with the exception of certain varieties of talc, have never been observed in crystals, the important labours of the crystallographer have not been able to throw any light upon them. But, as all mineral species are chemical compounds, and as each species consists of the same constituents united in the same proportions, I thought it not unlikely that an accurate chemical analysis of the different varieties of minerals, at present classed under the names Asbestus, Chlorite, and Talc, would be likely to throw considerable light on their nature, and would inform us whether they constitute peculiar mineral species, or are only varieties of species already well defined and characterized. I propose, in this paper, to give an account of the result of this investigation.

III. On a New Combustible Gas

It has been generally known for several years, that, when the acetic acid formed by the distillation of wood is rectified, there is obtained a transparent spirituous liquor, analogous in many respects to alcohol, though very different in others. This liquid has received the name of pyroxylic spirit . It is manufactured by Messrs Turnbull and Ramsay of Glasgow. I have been in the habit for several years of employing it for combustion in lamps instead of alcohol. It is a good deal cheaper, and raises just as good a heat as alcohol; for I can make the small platinum crucible, which I use for drying the products of analysis, red-hot by means of a pyroxylic spirit lamp in a few minutes. Pyroxylic spirit is as limpid and colourless as alcohol. Its specific gravity, when well rectified, is 0.812. It has an agreeable smell, not, however, quite free from that of naphtha. Its taste is very disagreeable, owing, I believe, to a small portion of naphtha, or empyreumatic oil, which it holds in solution, and from which we cannot free it by any known process. A set of experiments on pyroxylic spirit by Messrs Macaire and Marcet was published in the Bibliotheque Universelle for October 1823. These gentlemen have described several of its properties, and subjected it to an analysis, from which it appears that, like alcohol, it is composed of hydrogen, carbon and oxygen, though the atomic proportions are different.