The life of the Hon. Henry Cavendish : including abstracts of his more important scientific papers, and a critical inquiry into the claims of all the alleged discoverers of the composition of water / by George Wilson.

George Wilson

Date:: 1851

Credit: The life of the Hon. Henry Cavendish : including abstracts of his more important scientific papers, and a critical inquiry into the claims of all the alleged discoverers of the composition of water / by George Wilson. Source: Wellcome Collection.

487/508 page 463

$In further trials the nitric acid was largely diluted with water, and when exposed to a low temperature was found to congeal in part, so as to present the appearance of flakes or spicu as of ice floating through a syrupy liquid. This liquid was decanted from the crystals and ts strength determined by saturating it with marble; and the crystals, after liquefaction, were treated in the same way. They were found to consist, in%reater part, of pure water, whilst the unfrozen liquid was strongly acid From these experiments Cavendish drew the conclusion that nitric acid, or as he called it spirit of nitre, is subject to two kinds of conge- lation, which we may call the aqueous and the svvntmus; as m the farst it is chiefly if not entirely the watery part which freezes, and in the latter the spirit \i. e. the acid] itself. Accordingly, when the spirit is cooled to the point of aqueous congelation, it has no tendency to dissolve snow and produce cold thereby, but on the contrary is disposed to part with its own water; whereas its tendency to dissolve snow and produce cold, is by no means destroyed by being cooled to the point of spirituous congelation or even by being actually congealed. . Experiments of a similar nature were made with oil of vitriol, which was frozen at a temperature of -15°. It was allowed to melt partially in a warm room, and the fluid part was then decanted, but was not found to difler sensibly in strength from the undecanted portion of the acid. In other experiments snow was added to the diluted oil of vitriol, as in the preceding experiments to the nitric acid, till it began to fall in tempera- ture, which it did speedily. When snow was then rapidly added ^to it, the temperature of the air being —3-9°, the mixture sunk to —55^°. In another trial the thermometer descended to —68^°, and in a third to -78i=, a greater cold than had certainly been produced up to this time. Oil of vitriol was also shown to be capable of the spirituous congelation, and to freeze with a less degree of cold when strong than when much diluted; but Cavendish could not at this time make out that it had any point of easiest freezing. During the congelation, however, of oil of vitriol, he thought, both from his own experiments and from those of others, some separation of its parts took place, so that the congealed portion difiered in some respect from the rest, and in consequence froze with a less degree of cold ; and as he could detect no difference between the strength of^the congealed and uncongealed portions of the oil of vitriol, he thought it must be owing to the presence of some peculiar substance—. probably that which makes glacial sulphuric acid differ from common oil of vitriol. He then refers to the separability from the glacial acid, by the gentlest heat, of a peculiar concrete substance in the form of saline crystals; but that this was anhydrous sulphuric acid, and that glacial and common oil of vitriol differed from each other only in the proportion of this substance which they contained, he was not aware. A reference is then made to the action of a mixture of oil of vitriol and spirit of nitre on snow, which does not call for special notice, and the paper concludes with an account of experiments on the congelation of spirits of wine. Little cold was found to be produced when the spirits were mixed with snow. When diluted spirit was exposed to the natural cold of the atmo- sphere, it froze in part. The congealed portion consisted in greater part of water, what had not frozen retaining the spirit. Not satisfied in some respects with the results we have been consider- ing. Cavendish, with that extraordinary love of accuracy which he carried into every inquiry, had a second series of trials made by Mr. McNab.' The report of these is entitled, An Account of Experiments made by$