66 THE I'KlNCirLE.S OF AGKICLLTUKE. 



of the water, some of the remaining' salt would innnedi- 

 ately move forwanl and fill the vacancy, so as to maintain 

 an equal distribution. 



The diffusion of water and sulphuric acid may be seen 

 by partially tilling' a glass jar or tube with water colored 

 with blue litmus, and pouring through a tube, to the 

 bottom, water containing a few drops of sulphuric acid. 

 The effect of the acid would be to change the blue to 

 red. Sulphuric acid is heavier than water, and would 

 otherwise remain at the bottom ; but according to the 

 law of diffusion, it gradually mingles with the water 

 aljove until the color of the whole is changed to red. 



2. Osmose. — The term osinosi', from a Greek word 

 which means to push, is applied to the fact that sub- 

 stances which tend to mingle by diffusion will })ass 

 through a porous partition sejjarating them, and become 

 as thoroughly mixed as if no partition were present. If 

 a quantity of salt water and a quantity of sweetened 

 water are separated by a porous membrane, some salt 

 will j>ass through the membrane one way, and souie sugar 

 tlie other way, until both are equally distributed through 

 the whole. 



The same is true of other substances dissolved in 

 water, and of different liquids separated by a membra- 

 nous partition. 



This jii'inciple may l)e illustrated by placing in al)lad- 

 der, or some other membrane, a small (piantity of colored 

 alcohol, lowering this into a glass of water, and allowing 

 it to I'cniain until tlic water becomes colored, showing 

 that some of the alcohol has ]iasscd through the niem- 

 bi-anc into the wat(M'. 



While the mciiibran;', or other sulistance, must ]»e 

 porous, the pores may be very minute. Water, and sub- 



