14 ATTRACTION. 



called Capillary* attraction, has been considered by some 

 a species of the attraction of cohesion. Thus, if a glass 

 tube of very small bore, open at both ends, be immersed 

 in a vessel of water, the water will be found to rise higher 

 than its natural level. If a piece of sugar or salt be 

 placed upon a drop or two of water, the water will, by 

 virtue of this attraction, continue to rise in the sugar or 

 salt until it be entirely wet. Also the ascent of water to 

 the branches of trees by means of their roots, is attri- 

 buted to this kind of action. 



Chemical attraction, or affinity, is that principle on 

 which the various operations of chemistry depend. The 

 art of chemistry exerts itself to destroy the cohesion of 

 bodies, and to form other substances by means of new 

 attractions. Most bodies combine only in certain pro- 

 portions, and with certain other bodies ; and when com- 

 bined they acquire new properties, and cannot be sepa- 

 rated by mechanical means. There are 'two kinds of 

 chemical attraction, simple and compound attraction. 



Simple attraction, or affinity, is when two substances 

 unite together in consequence of their mutual affinity ; 

 thus, spirits of wine will dissolve camphor, and hold it in 

 solution, and the solution will be perfectly clear until 

 some other substance be added for which it has a greater 

 affinity than it has for the camphor ; water is such sub- 

 stance, a little of which being poured into the solution, 

 the spirits of wine will leave the camphor to unite with 

 the water, and the camphor will fall down in flakes. 



Compound affinity is when two compound substances 

 decompose each other, and produce two or more new 

 compounds. If a solution of muriate of baryta be mixed 

 with a solution of sulphate of soda, the sulphuric acid 

 of the sulphate of soda, by attracting the baryta of the 

 muriate of baryta, will form a sulphate of baryta, while 



* Sir Richard Phillips ascribes that which is generally called Ca- 

 pillary attraction to the pressure intercepted by the intervening sides 

 of the immersed solid, and which is relatively increased on the inter- 

 cepted side ; and that it is this important principle of intercepted 

 pressure which occasions a plurab-line to incline towards a moun- 

 tain, and boats to congregate about a ship, and small corks about a 

 bung. 



