On the 17th of April 1823, he communicated to the Royal Society a paper "On the application of Liquids formed by the condensation of Gases as mechanical agents."
He states that doubts may, for various philosophical reasons, exist as to the economical results to be obtained by employing the steam of water under great pressures, and at very elevated temperatures; but that no doubts can arise with respect to the use of such liquids as require for their existence even a compression equal to that of the weight of thirty or forty atmospheres; and where common temperatures, or slight elevations of them, are sufficient to produce an immense elastic force; and when the principal question to be discussed is, whether the effect of mechanical motion is to be most easily produced by an increase or diminution of heat by artificial means.
With the assistance of Mr. Faraday, he made several experiments on the differences between the increase of elastic force in gases under high and low pressures, by similar increments of temperature. In an experiment made with carbonic acid, its force was found to be nearly equal to that of air compressed to one-twentieth at 12° Fah. and of air compressed to one-thirty-sixth at 32 degrees, making an increase equal to the weight of thirteen atmospheres by an increase of twenty of temperature!
In applying, however, the condensed gases as mechanical agents, Davy admits that there will be some difficulty; "the materials of the apparatus must be as strong and as perfectly joined as those used by Mr. Perkins in his high-pressure steam-engine: but the small differences of temperature to produce an elastic force equal to the pressure of many atmospheres, will render the risk of explosion extremely small;" and he adds, "that if future experiments should realize the views here developed, the mere difference of temperature between sunshine and shade, and air and water, or the effects of evaporation from a moist surface, will be sufficient to produce results, which have hitherto been obtained only by a great expenditure of fuel."
If this be true, who can say that future generations shall not perform their voyages in gas-vessels, across the Atlantic Ocean, with no other fuel than that which a common taper may supply? I fear, however, that in this scientific reverie, Davy merely looked at the difference of the sensible temperatures, and entirely neglected, in his calculation, the quantity of heat rendered latent during the change of the liquid into the gaseous state; and which, perhaps, is far more considerable in the application of these fluids than in that of water; but even in this latter case, the great expenditure of heat in working the steam-engine, is in the portion rendered latent, and which cannot, by any contrivance, be brought again into operation, after it has performed its duty. That a philosopher who had, during the whole progress of his researches, directed such unremitting attention to the subject of Heat, should have wholly overlooked an objection arising out of one of its most familiar phenomena, is scarcely less extraordinary than his having, on another occasion,[82] advanced to a conclusion in direct opposition to the very principle of Electricity, which his own discoveries had established.
Davy succeeded in liquefying gases by a method which, at first view, appears very paradoxical—by the application of heat! The method consists in placing them in one leg of a bent sealed tube, confined by mercury, and applying heat to ether, or alcohol, or water, in the other end. In this manner, by the pressure of the vapour of ether, he liquefied prussic gas and sulphurous acid gas; which gases, on being reproduced, occasioned cold.
There can be little doubt, he thinks, that these general facts of the condensation of the gases will have many practical applications. They offer, for instance, easy methods of impregnating liquids with carbonic acid and other gases, without mechanical pressure. They afford means of producing great diminutions of temperature, by the rapidity with which large quantities of liquids may be rendered aëriform; and as compression occasions similar effects to cold, in preventing the formation of elastic substances, there is great reason to believe that it may be successfully employed for the preservation of animal and vegetable substances for the purposes of food.
Davy might also have added, that the same general views will explain natural and other phenomena not previously understood. They certainly afford a plausible explanation of the nature of blowers in coal-mines; and they may lead to more satisfactory views on other subjects of geology. They assign a limit to the expansive force of gas under increasing pressure, and account for effects connected with the blasting of rocks, which would otherwise appear anomalous.[83]
It may be stated, greatly to the honour of Davy, that there never occurred any question of scientific interest or difficulty in which he did not cheerfully offer his advice and assistance. Few Presidents of the Royal Society have ever exerted their influence and talents with so much unaffected zeal for the promotion of scientific objects, and for the welfare of scientific men. In the year 1821, the Great Hafod copper-works, in the neighbourhood of Swansea, were indicted for a nuisance, in consequence of the alleged destructive effects of the fumes which arose during the smelting of the ores. When we learn that the amount of wages paid by the proprietors of the works in this district exceeds 50,000l., per annum; that twelve thousand persons, at least, derive their support from the smelting establishments; that a sum of not less than 200,000l. sterling is annually circulated in Glamorganshire and the adjoining county, in consequence of their existence; that they pay to the collieries no less than from 100,000l. to 110,000l. per annum for coal; that one hundred and fifty vessels are employed in the conveyance of ore, and, supposing each upon an average to be manned by five seamen, that they give occupation to seven hundred and fifty mariners, a more serious calamity can scarcely be imagined than the stoppage of such works: we may therefore readily believe, that Davy entered most ardently into the consideration of some plan by which the fumes might be prevented, and the alleged nuisance abated.
Through the kind attention of my friend Mr. Vivian, I am enabled to insert the following letters.