130 THE SPIRIT OF THE SOIL 



A reaction very commonly met with is the change 

 of substances through the addition of the elements 

 of water. This is often effected by boiling the sub- 

 stance with dilute acid. Thus, the sugar Lactose, 

 if boiled with dilute Hydrochloric acid, yields the 

 sugars Glucose and Galactose, a molecule of water 

 being added in the process according to the 

 formula : 



C 12 H 22 O n + H 2 = C 6 H 12 6 + C 6 H 12 6 



Lactose. Water. Glucose.* Galactose.* 



At first sight it seems curious that the effect of 

 boiling with such a substance as a dilute acid should 

 be to add the elements of water. It has to be 

 remembered that when such a body as Hydrochloric 

 Acid is in solution it splits up. The molecules of the 

 acid no longer move in the liquid as the unit HC1, 

 but in a peculiarly active form as H and Cl , con- 



* These two substances, though they have the same composi- 

 tion, and in a sense the same structural formulae, have their 

 atoms differently arranged, so that one would be the looking- 

 glass picture of the other. 



