Volume 1

The principles of chemistry / by D. Mendeléeff.

  • Dmitri Mendeleev
Date:
1905
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The principles of chemistry / by D. Mendeléeff. Source: Wellcome Collection.

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    separation of Chemistry as a special branch of natural philosophy. Not only was this owing to the increasing store of observations and experi- ments relating to the transformations of substances, but more especially because, in addition to gravity, cohesion, heat, light, and electricity, it became necessary to recognise the existence of peculiar internal forces in the ultimate parts of all substances, forces which make themselves manifest in the transformations of substances into one another, hut remain hidden (latent) under ordinary circumstances, and whose exist- ence cannot therefore be directly apprehended, and so for a long time remained unrecognised. The primary object of chemistry is the study of the homogeneous substances 2 of which all the objects of the universe of substances as yet unknown to experiment, &c.), and have verified the knowledge thus obtained, and employed it for increasing the interests of humanity. It may therefore be safely said that the inductive method of investigation is a more perfect mode of acquiring knowledge than the deductive method alone (which from a little of the unknown accepted as incontestable arrives at much which is visible and observable) by which the ancients strove to embrace the universe. By investigating the universe by an inductive method (endeavouring from the much which is observable to arrive at a little which may be verified and is indubitable), the new science refuses to recognise dogma as truth, but through reason, by a slow and laborious method of investigation, strives for and attains to true deductions. 2 Substance or matter is that which occupies space and has weight; that is, which presents a mass attracted by the earth and by other masses of matter, and of which the objects of nature are composed, and by means of which the motions and phenomena of nature are accomplished. It is easy to discover, by examining and investigating in various ways the objects met with in nature and in the arts, that some of these are homogeneous, whilst others are composed of a mixture of several homogeneous substances. This is most clearly apparent in solid substances. The metals used in the arts (for example, gold, iron, copper) must be homogeneous, otherwise they are brittle and unfit for many purposes. Homogeneous matter exhibits similar properties in all its parts. By breaking up a homogeneous substance we obtain parts which, although different in form, resemble each other in their properties. Glass, pure sugar, marble, salt, &c., are examples of homogeneous substances. Examples of non- homogeneous substances are, however, much more frequent in nature and the arts. Thus the majority of the rocks are not homogeneous. In porphyries bright pieces of a mineral called ‘ orthoclase ’ are often seen interspersed amongst the dark mass of the rock. In ordinary red granite it is easy to distinguish large pieces of orthoclase mixed with dark semi-transparent quartz and flexible laminae of mica. Similarly, plants and animals are non-homogeneous. Thus, leaves are composed of skin, fibre, pulp, sap, a green colouring matter, &c. As an example of non-homogeneous sub- stances artificially produced, gunpowder may be cited, which is prepared by mixing together sulphur, nitre, and charcoal. Many liquids, also, are not homogeneous, as may be observed by the aid of the microscope, when drops of blood are seen to consist of a colourless liquid in which red corpuscles, invisible to the naked eye owing to their small size, are floating about. It is these corpuscles which give blood its peculiar colour. Milk is also a transparent liquid, containing microscopic drops of fat, which rise to the top and form cream when the milk is left at rest. It is possible to extract from every non-homogeneous substance those homogeneous substances of which it is made up. Thus orthoclase may be separated from porphyry by breaking it off. So also gold is extracted from auriferous sand by washing away the mixture of clay and sand. Chemistry deals only with the homogeneous substances met with in nature, or extracted from natural or artificial non-homogeneous substances. The various mixtures found in
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