172 



CHEMISTRY. 



expressed by some simple multiple of the first pro- 

 portion. Upon this general foct, doctor Wollaston 

 constructed the logametric scale of chemical equi- 

 valents ;in invention which has contributed, in an 

 cniincnt degree, to render our knowledge of the con- 

 stitution of compounds precise, by introducing the 

 sure basis of arithmetical relations, which, when fixed 

 with accuracy, are not susceptible of change. The 

 doctrine of definite proportions may, therefore, be re- 

 garded as having communicated to the principles of 

 diemistry that certainty which lias long been con- 

 sidered as peculiar to the mathematical sciences ; and 

 it is ni the development of these important relations 

 that the advancement of the science lias been most 

 conspicuous. Among the still more recent improve- 

 ments in chemistry may be cited the discovery of 

 Dobereiner, relating to the power of platinum in 

 effecting the combination of oxygen and hydrogen ; 

 the researches of Faraday, in which many ot the 

 gases have been reduced to the liquid form ; tiie 

 discovery of new compounds of carbon and hy- 

 drogen, and the singular feet, which they exhibit, 

 of different combinations being established in the 

 same proportions ; the elucidation of the new com- 

 pounds of chlorine with carbon ; of the peroxide of 

 chlorine ; the hydriodide of carbon ; the perchloric, 

 iodous, fulminic, and other acids ; the discovery of 

 the real bases of silex and zircon, and that of the new 

 principle, brome : add to these, that our knowledge 

 of light and electricity has been greatly enlarged, and 

 that the phenomena of electro-magnetism are alto- 

 gether new, and it becomes strikingly obvious that 

 chemistry is still a progressive science. " Nor can 

 any limits be placed to the extent of its investiga- 

 tions. Its analysis is indefinite ; its termination will 

 have been attained only when the real elements of 

 bodies shall have been detected, and all their modi- 

 fications traced : but how remote this may be from 

 its present state we cannot judge. Nor can we, 

 from our present knowledge, form any just concep- 

 tion of the stages of discovery through which it has 

 jet to pass " 



Chemistry has two ways of becoming acquainted 

 with the internal structure of bodies, analysis and 

 synthesis (decomposition and combination). By the 

 former, it separates the component parts of a com- 

 pound body ; by the latter, it combines the separated 

 elements, so as to form anew the decomposed body, 

 and to prove the correctness of the former process. 

 These methods depend on a complete knowledge of 

 the two powers, by which all bodies in nature are set 

 in motion, viz. , attraction and repulsion. Attempts 

 have been made to distinguish the attraction of ele- 

 mentary particles from planetary attraction; the 

 former being designated as chemical affinity: but 

 nature has only one kind of attraction. The alter- 

 nate play of attraction and repulsion produces a 

 great number of sensible phenomena, and a multi- 

 tude of combinations, which change the nature and 

 the properties of bodies. The study of these pheno- 

 mena, and the knowledge of these combinations, ap- 

 pertain to the department of chemistry. The history 

 of a body must always precede its analysis. The 

 mere examination of its form, its colour, its weight, 

 and the place where it was found, &c.. is often suf- 

 ficient, by a comparison, to lead to a knowledge of 

 its chemical properties. There is no science more 

 extensive than chemistry, nor is it possible for one 

 person to embrace it in its whole extent. To facili- 

 tate the study, it is considered in different points of 

 view, and thrown into divisions and subdivisions, so 

 that a person may devote himself to one department 

 of it, although the method of observing, analyzing, 

 and combining is the same in all, and although all 

 the phenomena must be explained by the general 



theory, and refer to certain laws, of wliicli a [ revious 

 knowledge is requisite. '1 hese laws constitute what 

 is called philosophical chemistry, which explains what 

 is meant by the affinity of aggregation or cohesion, 

 and by the affinity of coini>o>iti(in, or chemical affi- 

 nity. It treats of the phenomena of solution, situ- 

 ration, crystallization,ebullition, fusion, neutralization. 

 Chemical processes, by changing or modifying the 

 properties of bodies, suggest to the observer impor- 

 tant considerations on the changes of form, density, 

 and temperature. Philosopliical chemistry weighs 

 these considerations. It shows, further, that affinity 

 may be exerted, 1. between two simple bodies ; 

 2. between a simple and a compound one ; 3. be- 

 tween compound bodies ; and, establishing the prin- 

 ciple, that the same body has not the same aft nity 

 for all others, but attracts them unequally ; it shows 

 us the laws which determine tin's preference, and the 

 circumstances which modify it; such as cohesion, 

 mass, insolubility, elasticity, and temperature. It 

 measures the degree of affinity, whether of simple or 

 compound bodies. It observes the circumstances 

 wliicli aid or obstruct the play of attraction, and 

 shows that two bodies will not act upon each other, 

 unless one of them, at least, is in a fluid state ; that 

 bodies, even in a state of solution, act upon each 

 other only at imperceptible distances ; tliat two bo- 

 dies, which have no perceptible affinity, may be 

 made to combine by the interposition of a third ; and, 

 finally, that the peculiar properties of bodies are de- 

 stroyed by their combination, and the compound 

 possesses entirely new properties. Proceeding from 

 these principles to the examination of bodies them- 

 selves, philosophical chemistry considers the effects 

 of light, heal, and electricity ; the nature of the sim- 

 ple and compound inflammable bodies ; of air and 

 water ; the composition and decomposition of acids ; 

 the nature and properties of the salts ; their relations 

 to the acids ; the calcination, solution, and alloying 

 of metals ; the composition and nature of plants ; 

 the characteristics of the immediate elements of vege- 

 table substances ; the phenomena of animalization ; 

 the properties of animal compounds, and the decay 

 of organic substances. This is the sphere of philo- 

 sophical chemistry, while it confines itself to general 

 views. 



According to the application of these general 

 views, chemistry is divided into seven or eight 

 branches, which we have yet briefly to survey. '1 he 

 study of the great phenomena which are observed in 

 the atmosphere, and which are called meteors, con- 

 stitutes meteorological chemistry. Tliis explains the 

 formation of the clouds, rain, mist, snow, water- 

 spouts ; the state of the atmosphere in relation to 

 the hygrometer, barometer, and thermometer ; the 

 nature of the aurora borealis, meteoric stones ; in 

 short, all the chemical processes going on above the 

 surface of the earth. Geological chemistry treats 

 principally of the great combinations of nature, which 

 produce volcanoes, veins of metals, beds of mineral 

 coal, basalt, mineral waters, the enormous masses of 

 salt and lime, the saltpetre in the bed of the Indus, 

 the natron of the lakes of Egypt, the borax of the 

 lakes of Thibet. The geological chemist endeavours 

 to discover and explain the causes of deluges, earth- 

 quakes, the decrease of the waters on the globe, the 

 influence of climate on the colour of animals and 

 plants, on the smell of flowers, and the taste of 

 fruits. In these general views, he needs the aid of 

 natural philosophy and physics. Chemistry, in its 

 application to natural history, is divided in the same 

 manner. There is a chemistry of the mineral king- 

 dom, wliich comprises metallurgy and assaying, and 

 the examination of all inorganic substances, as stones, 

 salts, metals, bitumen, waters; a chemistry of the 



