COHESION. 



35 



tween the metal and the sides of the bowl ; but if 

 we turn the same into a metallic vessel, the surface 

 will be hollow or concave, because the metal is at- 

 tracted by the sides of the vessel. A gold c( in 

 dipped in quicksilver will be so coated with it in a 

 short time that it cannot be wiped off. An amal- 

 gam is formed by chemical affinity, and the gold be- 

 comes soft and white. So pieces of tin, placed 

 upon melted lead, will swim, because specifically 

 lighter than lead ; but on melting, which it will in a 

 short time, we find it diffused, by the influence of 

 affinity, through every portion of the lead. If we 

 throw rock-salt into water, it sinks ; in a few minutes 

 it is dissolved, and we then find every particle of 

 the water impregnated with salt. It has been at- ' 

 tracted in every direction by chemical affinity. 

 The same is the case with sugar, and every other 

 substance which has an affinity for water. When 

 we mix alcohol and water together, at first we find 

 a mere mechanical mixture ; in a short time, how- 

 ever, the fluid appears uniformly the same, because 

 they have chemically combined. 



Remarkable changes occur by the combination of 

 different substances. If we mix copper^ which is of 

 a reddish colour, with tin, which is white, we have 

 a compound of a grayish yellow of a very hard tex- 

 ture, although both copper and tin are soft. And, 

 what is more singular, though copper is not one of 

 the heavy metals, and tin is lighter still, the com- 

 bined mass weighs more than both. Now b%ll-metal 

 is made of tin and copper ; though a bell of tin 

 would have no sound, and one of copper would 

 sound duller yet. The same compound constitutes 

 bronze, oi which cannon, speculum, statues, &c., are 

 cast. Tin, combined with lead, forms one of the 

 best solders. Pewter is an alloy of tin 100 parts, 

 and antimony 17 parts. 



The air we breathe is composed of two poison- 

 ous gases ; and table salt is the result of a combi- 



