The elements of experimental chemistry (Volume 1).

  • Henry, William, 1774-1836.
Date:
Nov. 1814
Catalogue details

Licence: Public Domain Mark

Credit: The elements of experimental chemistry (Volume 1). Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    affinities of sulphurate acid for different bases, will be exactly the reverse of the order established by Mr. Kirwan ; and to that or- der, which would have been assigned from observed decomposi- tions. ' Thus ammonia will have a sronger affinity for sulphuric acid, than any of the substances which arc placed above it in the table; though it is separated, by each of these, from its union with that acid. It is in the extraneous forces, which have been enumerated as influencing chemical affinity, that we are to seek for the expla- nation of this apparent anomaly, and especially in those of cohe- sion and elasticity. The elasticity of ammonia, for example, turns the balance in favour of magnesia, lime, &c. There is an obvi- ous difficulty, however, in the application of the theory. For as the elasticity of ammonia, is suppressed by its combination with sulphuric acid, what, it may be asked, but a superior affinity can oc- casion the first commencement of decomposition ? This difficul- ty, perhaps, will be removed, if we admit that the affinity of the last portions of ammonia, which produce saturation, is inferior to the affinity of lime, which, being in an insulated state, acts on the sulphuric acid with all the force of its initial affinity. The de- composition then goes on because the ammonia, being removed from the sphere of action, presents no obstacle by its quantity. The problem, therefore, of determining the absolute forces of affinity can scarcely be admitted to be solved. Even if it were, we should not be able to predict the order of decomposition, unless the modifying forces of cohesion, elasticity, &c. could be at the same time subjected to precise admeasurement. Until both these ob- jects are accomplished, the results of chemistry can in no case be obtained by calculation, but the science must remain a collection of general principles, derived from experiment and induction. SECTION VI. Of Complex Affinity. • Under the more general name of Complex Affinity, Berthollet includes that which has hitherto been considered as produced by the action of four affinities, and which has commonly been denom- inated double elective affinity. It frequently happens that the < ompound of two principles cannot be destroyed either by a third