Tables and diagrams illustrative of chemistry and pharmacy / by John Murray.

Date:
1835
Catalogue details

Licence: Public Domain Mark

Credit: Tables and diagrams illustrative of chemistry and pharmacy / by John Murray. 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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    ]11 I have stated, in each instance, what it is the object of the reaction to form, and have marked the pharmaceutic processes of the Edinburgh College, and some of those peculiar to the Pharmacopoeias of London and Dublin. The equivalent numbers exhibit the proportional quanti- ties of materials that are necessary to decompose each other, and the amount of each product. But in Pharmacy, and in Practical Chemistry, quantities somewhat different are em- ployed ; the general rule being, to use an excess of the cheaper ingredient, as this ensures the complete decomposition of that which is more expensive. In our Pharmacopoeia this princi- ple is carried much too far ; and Dr Barker even found, in re- modelling the Dublin Pharmacopoeia, that in many cases the proportions of materials which it was most economical to use were such as agreed with the atomic numbers. Among the following cases of reaction may be remarked some of a singular kind, in which substances of a complicated constitution are resolved, by reaction between their elements, into substances altogether different. Thus, the salt named Nitrate of Ammonia is resolved by heat into water, and a gas named Nitrous Oxide ; the animal principle Urea is converted by the action of water into carbonate of ammonia, oxalic acid is resolved into carbonic acid and carbonic oxide gases, sugar into carbonic acid gas and alcohol ; and there are va- rious other examples of this nature. To illustrate these, the form of diagram, here employed, is peculiarly fitted, as it en- ables us to demonstrate the correspondence of atomic weights, and to shew how, by a different arrangement of atoms, one compound is convertible into another. Cases of this kind are the more interesting, as they may be considered as so many proofs of the accuracy of the atomic doctrine.