898 Notices respecting New Books. 



account of them, ami as far as possible in the very words 

 of the aiithor. After stating the nature of combination as 

 exemplified in combining oil and water by means of a so- 

 lution of potash, the latter having an attraction or affinity 

 for the former, it is observed that a new substance is formed 

 which differs from both the oil and alkaii in taste, smell, 

 colour, and in all its sensible qualities It is a general 

 character of chemical combinati.)n, that it changes the sen- 

 sible qualities of bodies. " The forms of bodies, or their 

 densities, likewise usually alter; solids becinue fluids, and 

 solids and fluids gases, and gases are olten converted into 

 fluids or solids." Salts, gums, &c. dissolve in water; the 

 consumption of charcoal in our fires depends upon its unit- 

 ing with a part of the air, with which it forms an invisible 

 elastic fluid : mercury is rendered solid by being heated 

 with half its weight of tin, and a substance of this kind is 

 used for silvering mirrors. " The gas produced by the 

 combustion of charcoal is condensed by another gas pro- 

 cured from quicklime and sal ammoniac, when they are 

 mixed over mercury ; and the two invisible elastic fluids 

 form a white saline solid," (carbonat of ammonia used for 

 smelling salts.) Many substances may be made to unite 

 by chemical affinity or attraction : fossil alkali, sand and 

 glass of lead melted together form flint glass ; porcelain is 

 formed by heating together mixtures of different earths. 

 *' That chemical attraction may be exertetl between bodies, it 

 is necessary that they should be brought into apparent con- 

 tact. Thus, no body will act chemically upon another at 

 any sensible distance. A freedom of motion in the parts 

 of bodies, or a want of cohesion, greatly assists combina- 

 tion ; and this circumstance is so marked, tfjat it was for- 

 merly considered as a chemical axiom, which is still re- 

 tained in some elementary books, that bodies cannot act 

 chemically on each other, unless one of them be fluid 

 or aeriform. Such an extensive generalization is, however, 

 ■incorrect : thus, crystalline muriate of lime and snow, both 

 cooled to 0^ Fahrenheit, act upon each other and liquefy ; 

 and crystals of oxalic acid and dry lime, treated in the 

 same manner, readily combine. The hardest and the densest 

 bodies, however, undergo chen)ical changes with the 

 greatest difficulty. Thus the sapphire in its crystallized 

 state is not affected by boiling sulphuric acid ; but when 

 in a fine powder, as alnmine, it is easily dissolved. Mi- 

 nute division, or solution, or fusion, is necessary in almost 

 all chemical processes." These general and well known 

 facts prem^ised, relative to attraction and combination, the 



author's 



