Page:A biographical dictionary of eminent Scotsmen, vol 4.djvu/221

Rh and enriched its transactions by accounts of experiments on a bold and extensive scale. The results Avere in many instances so important, that they deserve to be cursorily mentioned in this memoir, which, treating of a scientific man, would be totally void of interest without some reference to them. He was a supporter of the theory of Dr Hutton, who maintained the earth to be the production of heat, and all its geological formations the natural consequences of fusion; and his experiments may be said to be special evidence collected for the support of this cause. Among the minute investigations made by the supporters of both sides of the controversy, it had been discovered by the Neptunians, that in some granites, where quartz and feldspar were united, the respective crystals were found mutually to impress each other therefore, that they must have been in a state of solution together, and must have congealed simultaneously; but as feldspar fuses with less heat than is required for quartz, the latter, if both were melted by fire, must have returned to its solidity previously to the former, and so the feldspar would have yielded entirely to the impression of the crystals of the quartz. Sir James Hall discovered, that when the two substances were pulverized, and mixed in the proportions in which they usually occur in granite, a heat very little superior to that required to melt the feldspar alone, fused both, the feldspar acting in some respects as a solvent, or flux to the quartz. Making allowance for the defects of art, the result of the experiment, while it could not be used as a positive proof to the theory of the Huttonians, served to defend them from what might have proved a conclusive argument of their opponents. But the other experiments were founded on wider views, and served to illustrate truths more important. The characteristic of the theory of Dr Hutton, distinguishing it from those of others who maintained the formation of the earth by means of fire, was, that perceiving the practical effect of heat on most of the bodies which formed the crust of the earth, to be calcination, or change of state, and not fusion, or change of form, and knowing from the experiments of Dr Black, that, in the case of limestones, the change depended on the separation of the carbonic acid gas from the earth, the theorist concluded, that by a heat beyond what human agency could procure, calcareous earths might be fused, provided the gas were prevented from escaping, by means of strong pressure. Sir James Hall, conceiving it possible that a sufficient heat might be procured, to exemplify the theory on some calcareous bodies, commenced a series of experiments in 1798, which he prosecuted through success and disappointment for seven years. The result of these experiments produced an elaborate paper, read before the Royal Society of Edinburgh, and published in the Transactions of that body in 1806 ; they were in number one hundred and fifty-six, some successful, others productive of the disappointment to which accident frequently exposes the zealous chemist, conducted with considerable danger, great expense, and unvarying patience and labour, and on the whole singularly satisfactory in their results. The plan followed by Sir James was, to procure a tube which might afford a strong resistance to inward pressure, for which purpose he alternately tried iron, and porcelain; one end being closed up, pulverized chalk or other limestone was inserted, and the space betwixt its surface and the mouth of the tube being closely packed with some impervious substance, such as clay baked and pounded, fused metal, &c., the open extremity was hermetically sealed, and the end which contained the substance to be experimented upon, subjected to the action of a furnace. The iron or the porcelain was frequently found insufficient to sustain the pressure; the substance rammed into the tube to prevent the longitudinal escape of the gas had not always the effect, nor could Sir James, even in the most refined of his experiments, prevent a partial though sometimes scarcely perceptible escape of gas; yet the general results showed the truth of