Volume 1

A system of chemistry / by John Murray.

  • Murray, J. (John), -1820.
Date:
1819
Catalogue details

Licence: Public Domain Mark

Credit: A system of chemistry / by John Murray. Source: Wellcome Collection.

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

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    not very great, as the affinity exerted by the one of tliese principles to the other is a force the effect of wliich is to maintain the combination, to counteract therefore the ele- mentary, and favour the resulting affinity. Lastly, when an elementary affinity is exerted at first, as it must become weaker in the approach to saturation, it will at length not exceed in force the affinity exerted to the other principle of the compound, an equilibrium will be established, and the action will terminate in the exertion of a resulting affi- nity. The application of these principles affords some hap- py explanations of more minute chemical phenomena, of which a few examples are given in the note beneath *. An important application of this doctrine is to be found in the explanation it affords of certain anomalous cases of * Water, in dissolving a neutral salt, acts by a resulting ^affi- nity, or by the astractions it exerts to the principles of the salt, modified by the attractions they exert to each other. But if its attraction to one of these principles be much superior to what it is to the other, especially where the affinity between them is not very strong, the affinity it exerts is elementary, and the salt is decomposed. This is exemplified in a number of the metallic salts, in which water abstracts their acid. Sulphuric acid is a compound of oxygen and sulphur, and, in combining with potash, is supposed to act by an affinity which results from the affinities of these elements. The reciprocal action of potash is also composed of its affinities to the prin- ciples which constitute sulphuric acid. Both therefore are re- sulting ; and when exerted, they effect the combination of the acid and potash. But the elementary affinities of sulphuric acid may also be exerted. Thus, when heated on a metal, the me- tal does not exert an attraction to the entire acid, but to its oxygen. This is therefore an elementary affinity ; but in the progress of the action, the attraction of the metal to an addi- tional portion of oxygen becoming nearly equal to its attrac- tion to sulphqr, at least when that attraction is aided by the attraction of the oxygen to sulphur, it exerts an affinity to