The London dispensatory : a practical synopsis of materia medica, pharmacy, and therapeutics : Illustrated with many useful tables, and woodcuts of the pharmaceutical apparatus / by Anthony Todd Thomson ; edited by Alfred Baring Garrod.

Date:
1852
Catalogue details

Licence: Public Domain Mark

Credit: The London dispensatory : a practical synopsis of materia medica, pharmacy, and therapeutics : Illustrated with many useful tables, and woodcuts of the pharmaceutical apparatus / by Anthony Todd Thomson ; edited by Alfred Baring Garrod. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    some cases, the change is sudden, or the body instantly passes from the solid to the liquid state; in other cases, it passes through several degrees of softness before it be perfectly liquefied: the conversion of ice into water is an example of the first; the melting of glass, of wax, and unctuous matters, which become first viscous, are instances of the second. There are some bodies, nevertheless, which cannot be melted or fused, owing to their suffering chemical decomposition at a lower temperature than is required for their fusion under the ordinary pressure of the atmosphere : — a piece of wood, for instance, cannot be melted by the application of any degree of heat. Although the melting point, in most cases, is always the same in the same bodies, yet circumstances may vary it; and the admix- ture of other substances may alter it very considerably. Thus, the melting point of ice, or, what is generally the same thing, the freezing point of water, is 32°; but by exposing water slowly to the action of freezing mixtures, it may be cooled down to 22° before it freezes. The addition of salts renders this point still lower, as may be seen by the following table.1 Names of salts. Proportion by weight dissolved in 100 parts of water. Freezing point. Common salt 25* 4* Sal ammoniac 20 8* Rochelle salt 50 21- Sulphate of magnesia 41-6 25*5 Nitre - 12-5 26* Sulphate of iron 41-6 28- zinc 33-3 28*6 When solids pass to the liquid state they receive an additional quantity of heat, which combines with them, but does not sensibly elevate their temperature ; and this caloric of fluidity or latent heat, as it has been named, is again given out in a sensible form, when the body returns to a solid state. If water, for example, be ex- posed to a great degree of cold, and kept free from agitation, it may be cooled several degrees below the freezing point, namely, to 21°, and yet remain fluid; but if it be then agitated, it instantly congeals, and at the moment of its congelation its temperature Lead - - 612° Copper - 1996° Spermaceti - 112° Bismuth - - - 476 Silver - 1873 Phosphorus 100 Tin - - - 442 Iron - - 21637 Tallow 92 Zinc - - 773 Sulphur 218 Oil of anise 50 Antimony - - 809 Bees’ wax 149 Camphor 303 Mercury - - —39 Lard - 97 Ice 32 1 Phil. Trans. 1788, 27., quoted by Dr. Thomson, Syst. Chemistry, 4ih edit. i. 520.