CHEMISTRY. 



tXonhave been called tables of simple elec- 

 tive attraction. They are usually drawn up 

 to express effects in the humid way with 

 moderate proportions of water at the mid- 

 dle atmospheric temperature ; and in the 

 dry way by the operation of fire acting 1 

 up'on the containing vessels, to raise their 

 temperature. From the reasons just 

 mentioned, they cannot be admitted as 

 denoting invariable effects, but they are 

 nevertheless useful, provided the modifi- 

 cations of circumstances be attended to 

 in our general reasoning. See ELECTIVE 

 ATTRACTION. 



3. In our present discussion it was not 

 practicable, from the nature of the sub- 

 ject to avoid presenting facts for illus- 

 tration, in which more than three princi- 

 ples were concerned; though the doc- 

 trines to be elucidated supposed no more 

 than that number to be present. This 

 supposition can admit only of one combi- 

 natio! , either of two or of three princi- 

 ples ; but in the complex effects of che- 

 mical attraction, four or more bodies may 

 be treated of as forming distinct and se- 

 parate combinations ; and these com- 

 pounds being presented to each other, 

 may be affected by all the habitudes and 

 circumstances upon which we have so 

 long dwelled, besides such others as 

 arise from their greater complexity. 

 These cannot be' here fully treated. It 

 will be sufficient at present to overlook 

 those effects wherein compounds of many 

 principles may be formed, or in which 

 the intermediate, or resulting, or dis- 

 posing attractions may operate, and re- 

 gard only the cases in which two binary 

 compounds, being presented to each 

 other, do either remain unaltered, or else 

 exchange their principles so as to form 

 two other binary compounds. A few 

 years ago this was thought to compre- 

 hend the greatest part of the doctrine of 

 chemical attractions ; but, as practical 

 science advances, the supposed simplici- 

 ty of the facts becomes less than before. 



These phenomena, afforded by two bi- 

 nary compounds, have been classed un- 

 der the denomination of effects of dou- 

 ble elective attraction. These facts may 

 be considered with regard to the whole 

 force of the attractions that tend to re- 

 tain the original compounds, which have 

 been called quiescent attractions, and the 

 whole force of the attractions that tend 

 to produce two new binary compounds, 

 which have been called divellent attrac- 

 tions. If the former be the greatest, the 

 change will not take place ; but if the 

 latter exceed, it will. Thus, if to the 



s,ulphate of potash lime be presented, the 

 sulphuric acid being more strongly at- 

 tracted by potash than by lime, no de- 

 composition will ensue; but if muriate 

 of lime be presented to the sulphate of 

 potash, the lime will not only attract the 

 sulphuric acid, but the muriatic, acid 

 will attract the potash ; and the sum of 

 the divellent attractions, namely, of the 

 lime to the sulphuric acid, of the muri- 

 atic acid to the potash, being greater 

 than the sum of the original or quiescent 

 attractions; namely, of the sulphuric 

 acid to the potash, and of the muriatic 

 acid to the lime ; two new compounds, 

 namely, sulphate of lime and muriate of 

 potash, will be formed. See ELECTIVE 

 ATTRACTION. 



The most essential difference between 

 the complicated cases of attraction here 

 described, and those treated of just be- 

 fore, is, that the principles in these last 

 are either saturated, or nearly so, when 

 presented to each other ; and from this 

 difference, and the number of principles, 

 it is, that the effect of solvents, the force 

 of cohesion and of elasticity, as well as 

 of temperature, and other circumstances, 

 act with more effect than in the simpler 

 cases. 



Whenever the cohesive attraction ope- 

 rates so as to form solid aggregates, 

 whether by the congelation of fused bo- 

 dies by cooling, or the deposition of bo- 

 dies from their solvents, the aggregates, 

 if not disturbed by too rapid condensa- 

 tion, or by other causes, have the forrn 

 of solids bounded by flat surfaces, meet- 

 ing each other in certain definite angles. 

 These solids are called crystals. The 

 property of crystallizing seems to be a 

 natural consequence of the resulting at- 

 tractions. For if a binary compound be 

 attracted by any other principle or com- 

 pound, and the time and circumstances 

 allow the particles to turn round, it ap- 

 pears obvious that the appulse and ad- 

 hesion will be made by such sides of the 

 bodies as'are occupied by particles most 

 strongly attractive of each other ; and 

 this regularity of opposition must pro- 

 duce regularity of figure. See CRYSTAL- 

 LIZATION. 



After this general statement of the 

 means and agents of chemistry, it re- 

 mains only for us, in this general article, 

 to give an outline of the different sub- 

 stances or principles upon which the pro- 

 cesses of nature and art are performed,, 

 and upon which the articles devoted to- 

 each may be consulted. 



