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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    very considerable. An increased temperature, by promoting fu- sion, and in other respects weakening the attraction of cohesion in solids, favours combination; but opposes it in some cases, inasmuch as it augments elasticity. In both instances its effects are much modified by the degree of its intensity; combinations effected at a lower being often dissolved at a higher temperature, owing to one or more of the components having its affinity weakened by an in- creased elasticity. Thus, mercury exposed to air, for some time, at a temperature equal to its boiling point, combines with the oxygen of the air, and is converted into red oxide of mercury ; but, if the fire be raised so as to make the retort red hot, this oxide is again decomposed, and running mercury and oxygen gas are obtained. The order of affinity is also influenced by the nature of the at- mosphere in which the elements are placed: thus, steam passed over iron at a red heat, is partly decomposed, oxide of iron being formed, and the hydrogen of the steam set free ; but, if a stream of hydrogen gas is passed over oxide of iron at the same temperature, the oxide is decomposed, water is formed, and the iron, reduced to the metallic state, remains. In this manner the Pul vis Ferri of the Dublin Pharmacopoeia, the “ Fer reduit” of the French, is di- rected to be prepared. Here the difference of atmosphere, into which the disengaged products can diffuse, influences the nature of the decomposition, the atmosphere of steam favouring the dis- engagement of the hydrogen, and the hydrogen the formation of the watery vapour. From the influence of the above circumstances on chemical com- bination, the utility of those pharmaceutical and chemical opera- tions, which diminish aggregation, overcome the effect of specific gravity, diminish elasticity, and regulate temperature — such as pulverization, trituration, granulation, agitation, and compression, with the proper management of furnaces — is sufficiently obvious. In that department of pharmacy, also, which regards extempo- raneous composition, it is of importance to attend to the slowness with which chemical action is in many instances produced ; for substances, which have mutual affinities for each other, may give no indication of any change when newly mixed, but yet, after some time, produce very complete changes. Such compounds, therefore, when they are intended to act medicinally, should be exhibited as soon as possible after they are made. Chemical attraction may be exerted between more than two bodies, so as to bring three or four into one combination ; and such compounds are named ternary, quaternary, &c. according to the number of their components. Several examples of these are to be found among the saline preparations; and almost all the vegetable substances are compounds of three or more principles. The forces with which chemical attraction is exerted are differ- ent in different bodies. In cases where this attraction is exerted in a