CHEMISTRY. 



and the same power, or from energies 

 originally dissimilar, require, at least for 

 the purposes of language, to be treated 

 apart from each other. Chemistry seems 

 to have little to do with the perceptible 

 attractions : it is principally confined 

 to the state of bodies, as it relates to 

 the cohesion and the combination of their 

 parts. 



Heat, or rather temperature, is a well 

 known modification of bodies, by which 

 they produce a peculiar sensation, dis- 

 tinguished by the same word. Its laws 

 have been very successfully investigated 

 by our contemporaries ; for which see CA- 

 LORIC, HEAT, and COMBUSTION. The ope- 

 rative chemist considers it as the means 

 of converting solid bodies into dense 

 fluids, and dense fluids into elastic fluids, 

 called gas or vapour, while compound bo- 

 dies may have their parts separated from 

 each other by this treatment. 



When bodies of different kinds are 

 brought into contact, they produce very 

 little of the change called chemical, 

 while they continue in the solid state. 

 Mechanical trituration will forward their 

 mutual action, by multiplying the sur- 

 faces of contact ; but still the masses con- 

 tinue too large to be moved amongst 

 each other by the peculiar attractions 

 they may be capable of exerting. It has 

 been considered as an axiom in chemis- 

 try, that bodies do not act on each other, 

 unless one or both be in the fluid state ; 

 and though this is not strictly and uni- 

 versally true, yet it is requisite for almost 

 every operation of chemistry, that this 

 condition, either of dense or of elastic 

 fluidity, should obtain. The facility with 

 which the parts of fluids move amongst 

 each other is, no doubt, the principal 

 cause of this increased effect. 



The practical part of chemistry may be 

 therefore said to consist almost entirely 

 in separating or changing the order of 

 the parts of bodies by heat, or of placing 

 bodies in such situations with regard to 

 each other, as that, with the assistance 

 of heat, if needful to produce fluidity ; 

 changes or separations of the same kind 

 may take place among their parts. The 

 actions of electricity, galvanism, and 

 light, will probably be soon combined 

 among the leading resources of chemis- 

 try. 



No change could take place by this or 

 any other treatment, if the attractions of 

 the parts of bodies to each other were all 

 perfectly the same. It is manifest from 

 the facts, that the attractions between 

 some bodies is stronger than between 

 others, and from this remarkable variety 



in the habitudes of bodies, the attractions 

 of chemistry have been called elective 

 attractions. 



A distinction has been made between 

 those processes in which water is present, 

 and those in which the requisite fluidity 

 is produced by strong heat. The first me- 

 thod is called the humid way, and the 

 other the dry way. 



The practice of chemistry requires, in 

 most cases of solid bodies, previous to 

 the application of heat, or of one body 

 to another, for the exercise of the attrac- 

 tions, that some mechanical means should 

 be taken to divide their parts from each 

 other. These are, 1, chopping or cut- 

 ting ; 2, rasping, filing, or shaving ; 3, 

 pulverizing or grinding ; 4, granulation, 

 as when shot is formed by pouring lead 

 into water, or a powder of the metal is ob- 

 tained by shaking it in a box, in the fus- 

 ed state, till it congeals ; 5, elutriation, 

 or washing, to separate the finer or light- 

 er parts of bodies from the coarser or 

 larger, as when earthy matters are wash- 

 ed from the heavier metallic ones, or 

 when a fine powder, such as that of 

 pounded emery, is suspended by agita- 

 tion in water, which is decanted off, and 

 then set to subside, while the coarserpar- 

 ticles, which settle immediately, are left 

 behind ; 6, hammering, or forging, as in 

 the making of tin foil, or leaf gold, or in the 

 extension of other metals, whether hot 

 or cold ; 7, laminating, as when the metals 

 are passed between steel rollers, or 

 when wax is poured upon a wooden cy- 

 linder, turned round in cold water; and, 

 8, wire drawing, as when the metals are 

 drawn through a hole in a plate to make 

 wire, or forced through an engine, 

 such as that employed for glazier's lead, 

 &c. 



Bodies are distinguished, with regard 

 to heat, into fixed, volatile, and refrac- 

 tory. The first can scarcely, if at all, be 

 evaporated ; the second are easily raised 

 or driven off; and the third undergo no 

 change. 



The simple application of heat is dis- 

 tinguished by various terms, according to 

 the nature of the operation, or of the ef- 

 fects produced. These are, 1, roasting, 

 which consists in exposing minerals to an 

 open fire, to drive off their volatile con- 

 tents; 2, calcination is the exposure of a 

 body to strong heat, in an open vessel, 

 till it undergoes no farther change. This 

 word, which was formerly used in a ge- 

 neral way, is now confined to earths and 

 some of the salts, and is indeed seldom 

 used; 3, oxydatiou is the like process 

 with metallic bodies : 4, fusion, or melt- 



