The London dispensatory, containing: I, the elements of pharmacy; II, the botanical description ... and medicinal properties, of the substances of the materia medica; III, the pharmaceutical preparations and compositions of the pharmacopoeias of the London, Edinburgh, and Dublin Colleges of Physicians / By Anthony Todd Thomson.

  • Thomson, Anthony Todd, 1778-1849.
Date:
1830
Catalogue details

Licence: Public Domain Mark

Credit: The London dispensatory, containing: I, the elements of pharmacy; II, the botanical description ... and medicinal properties, of the substances of the materia medica; III, the pharmaceutical preparations and compositions of the pharmacopoeias of the London, Edinburgh, and Dublin Colleges of Physicians / By Anthony Todd Thomson. Source: Wellcome Collection.

    31/1096 (page 11)
    7. The influence of temperature in modifying chemical action is very considerable. An increased temperature, by promot- ing fusion, and in other respects weakening the attraction of cohesion in solids, favours combination; but opposes it in some cases, as much as it augments elasticity. In both in- stances its effects are much modified by the degree of its inten- sity; 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 increased 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 de- composed, and running mercury and oxygen gas are obtained. From the influence of the above circumstances on chemical combination, the utility of these pharmaceutical and chemical operations, which diminish aggregation, overcome the effect of specific gravity, diminish elasticity, and regulate tempera- ture, 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 extem- poraneous compositions, 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, may act, and produce even 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 (Part iii.) ; and almost all the vegetable substances are compounds of three or more principles. The forces with which chemical] attraction is exerted are dif- ferent in different bodies. In cases where this attraction is exerted in a superior degree, by a third body, to that of either of the components of a compound of two bodies, so as to decompose it, and form a new compound, while, at the same time, one of the components of the previous compound is set free, the affinity thus exerted has been termed single elective attraction. ‘lo represent the relative forces of affinity, tables were first constructed by Geoffroy ; and afterwards much