CHEMISTRY. 



ing, is the production of the state of 

 dense fluidity ; 5, cementation is a pro- 

 cess, wherein solid bodies of different 

 kinds, one or more of them being- in pow- 

 der, are exposed to heat in a vessel near- 

 ly closed, with the intention that the more 

 t volatile parts of the one may unite with 

 the other, or its fixed parts ; 6, eliqua- 

 tion is the exposure of a compound body, 

 usually metallic, to heat, sufficient to 

 fuse one of its ingredients, which runs 

 out, and leaves the other solid and po- 

 rous; 7, digestion consists in keeping bo- 

 dies for a considerable time immersed in 

 a fluid more or less heated, in order to 

 effect some combination between them ; 

 8, evaporation is the dissipation of a fluid 

 by heat ; 9, concentration consists in di- 

 minishing the proportion of water in any 

 solution of saline matter, either by heat- 

 ing it, or by freezing the surplus water 

 and taking out the ice ; 10, when evapo- 

 ration is performed in any apparatus of 

 vessels, partly or quite closed, and the 

 vapours, after being raised by heat in one 

 part or vessel, are received in another 

 sufficiently cold to condense them into 

 the fluid state, this process is called dis- 

 tillation; 11, when a fluid obtained by 

 distillation is again distilled, in order to 

 obtain the most volatile part of the first 

 product, this last part is said to be recti- 

 fied, and the process is called rectifica- 

 tion. This term has become nearly ob 

 solete in scientific description, but is still 

 retained in the arts; 12, there are many 

 products of evaporation, which congeal, 

 or become solid, at a temperature much 

 higher than that of the atmosphere, and 

 are not, therefore, obtained in the fluid, 

 but the solid state. These usually ad- 

 here in the form of crystals to the upper 

 part of the apparatus, and on this account, 

 as well as because the operation does not 

 in general require the same kind of ves- 

 sel, it is distinguished by the name of su- 

 blimation, and the products themselves 

 are called sublimates, and in some in- 

 stances flowers ; but these two last terms 

 are more particularly confined to the 

 arts. Other terms are also used, such as 

 fusible, evaporable, &c. but their sense is 

 manifest. 



For the apparatus used in these and 

 the other operations of chemistry, see 

 LABORATORY. 



The consideration of what happens to 

 the parts of bodies, in consequence of 

 their elective attractions, constitutes the 

 most difficult part of the science, whe- 

 ther the mind be employed in developing 

 the facts, or in deducing the general 

 theory which may be indicated from 



them. It is, therefore, necessary to con- 

 sider them with some attention, and in a 

 regular manner. 



The adhesion of parts, considered to 

 be of the same kind, is called lurivrega- 

 tion. Thus a number of piec. s o*-' ,lass 

 melted together form an aggregate : and 

 the smallest parts into which an aggre- 

 gate can be imagined to be divided, so 

 as not to change its nature, are called in- 

 tegrant parts; so that the integrant 

 parts of glass are themselves glass. But 

 when the body is known to be made up 

 of parts of different kinds or nature, and 

 it is considered with regard to these, the 

 body is called a compoond, or combina- 

 tion, and the parts are called component 

 parts or principles. In this manner 

 glass is a compound of the earth called 

 silex. and a salt called alkali, combined 

 together at a strong heat: and we may 

 imagine, that if there were any means 

 by which glass could be reduced, first 

 to its integrant parts, and the division 

 could be carried farther, the parts would 

 then be no longer integrant and glass, 

 but would become divided into compo- 

 nent parts, namely, earth, and alkali. 

 Bodies are also considered in a wide 

 manner by the name of mixtures, when 

 small aggregates of different kinds are 

 united, as in a variety of minerals, where 

 the parts are frequently distinguishable 

 by the senses : and in the arts we have 

 sand and lime made into mortar by mix- 

 ture, or sand, clay, and other earths, 

 made into pottery, and hardened by a 

 moderate fire ; but these by a stronger 

 heat may be made to combine into glass, 

 and are then no longer mixtures, but com- 

 pounds. 



The early chemists were led into a sup- 

 position, that the bodies they were un- 

 able to analyze were simple, and they 

 distinguished them by the name of ele- 

 ments. It is probable that the great va- 

 riety of bodies around us are formed by 

 combination, out of a few simple princi- 

 ples, or perhaps out of one single ele- 

 ment, variously combined as to figure and 

 position of parts ; but it*is useless and un- 

 profitable to speculate on probabilities, 

 which experiment can never verify. Mo- 

 dern chemists, very properly, consider 

 those bodies as simple, which have not 

 yet been decomposed ; but this is merely 

 with relation to the present state of 

 our knowledge, and for the sake of ar- 

 rangement and induction. They do not 

 lose sight of the necessity of instituting 

 experiments for their further analysis; 

 and the great discoveries which have 



