Copy 1

The London dispensatory / By Anthony Todd Thomson.

  • Anthony Todd Thomson
Date:
1811
Catalogue details

Licence: Public Domain Mark

Credit: The London dispensatory / By Anthony Todd Thomson. Source: Wellcome Collection.

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    inches and tenths. The length to which the pyrometrical pieces can be slid in the converging groove, indicates the heat to which they have been previously “exposed ; and as they do not expand again when cold, no fallacy can uae from the ac- tion of heat on the gauge. Each degree of this scale is eqnal to 130° of Fahrenheit; and the 0, or commencement of it, corresponds with 10774 of Fahrenheit’s scale. The hiohest temperature that Has Metti measured by it is 160° or 21:877° of Fahrenheit, which is 30° above the point at which cas iron melts. But as much higher temperatures than this must exist, so, also, there are temperatures much lower than can be measured by any thermometer. Hence all bodies contain a portion of caloric intimately combined with them, and which remains latent or insensible while they remain; but which may be extricated and rendered sensible by chemical action ; as in the processes of mixture cag combustion. Effects of Caloric. The effects produced by Hats ri6 on bodies are different both in degree and in kind. By the introduction of it inte substances in different quantities, they are either changed in bulk, and suffer expansion; or in state, assuming the fluid form, and that of vapour; or they are ivnited, a. Expansion, or increase of bulk, is ‘the most general effect of caloric, and, with very few exceptions, may be regarded as a wencral law of its operation. When caloric flows into a body, it separates its integrant particics from each other, and hence augments its volume. This change is smallest in solids, more considerable in liquids, and most considerable in gaseous bodies; or the expansibility is greater in the inverse ratio of the force of aggreration. Thus, the ¢ expansion of air 1s 8 times greater than that of water; and the expansion» of this 45 times greater than that of iron. The expansion of solid bodies i 1S, in general, so very Incon siderable as not to be easily ascertained ‘by measurement : re as far as it can be known, it is equable. Argi] is an excep- tion to the law of expansion in solids; for, as has been al- yeady remarked, the bulk of pure clay eer fo when heated, in the ratio of the intensity of the heat to which it is exposed, The cause of this anomaly has not been discovered. That of Jiquids is more evident, but not at all uniform; the differences apparently depending on the fixity or volatility of the compo- nents of the liquids: those expanding the most the boiling point of which is lowest ; and which, consequently, most readily assume the gaseous form. The degree of their expansion, also, increases with the augmentation of their temperature 5 or, the nearer a liquid approaches to the boiling point, the greater is the expansion produced by a degree of calonec ;
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