28 CHEMICAL AFFINITY IS 



atmospheric air, a gaseous mixture in which oxygen 

 forms only the fifth part, that metal (in the form 

 of a black powder) condenses on its surface, at 

 the ordinary temperature, an enormous quantity of 

 oxygen gas (without any nitrogen), and acquires 

 thereby properties, which it does not otherwise 

 possess.* And when oxide of chromium, fragments 

 of porcelain, or asbestus, at high temperatures, 

 effect the combination of two gases, oxygen and 

 hydrogen, or oxygen and sulphurous acid, which 

 gases do not combine at the same temperature, 

 unless when in contact with thee solid bodies, it is 

 to the chemical attraction or affinity of these solid 

 bodies that we must ascribe this effect. 



The solution of a salt in water is an effect of 

 affinity, and yet no one property, either of the salt 

 or of the solvent, is thereby altered, except only the 

 cohesion of the saline particles. 



Sea salt, the crystals of which are usually anhy- 



tion of sea 



salt. drous, takes up, at very low temperatures, 38 per 



cent, of water of crystallization ; not because any 

 new cause acts which increases its affinity for the 

 particles of water (for cold is no cause, but the 

 absence of a cause), but because the higher tem- 

 perature acted as an obstacle, opposing their 

 chemical combination. The force of affinity is 

 all the time present and undiminished. 



* According to Dcebereiner, platinum black condenses 252 times 

 its volume of oxygen. Its effect in oxidizing alcohol, pyroxilic 

 spirit, &c., is familiar to every chemist. W. G. 



