440 



THE FARMER S AND 



burning animal substances, called animal charcoal, which 

 is more effective than vegetable charcoal. Charcoal has 

 likewise the property of absorbing coloring matter ; bran- 

 dy may be rendered white by being passed through it, 

 and port wine has been rendered pale . it is also used for 

 whitening the syrup of sugar. 



Nature effects filtration by means of beds of sand.- 

 Water that has percolated through these issues is perfectly 

 transparent and clear, and freed from everything except 

 what it holds from solution. Art, imitating nature, em- 

 pioys sand for the same purpose, and filtering beds upon 

 a great scale have been formed for purifying water, the 

 supply of towns, and for domestic purposes. Little more, 

 indeed, seems necessary for rendering water perfectly 

 pure, where the impurities are merely of a mechanical 

 nature. 



To filter water "by means of sand, it is the practice in many 

 places, particularly in France, to 

 construct cisterns in the cellars, 

 and to divide them into two une- 

 qual parts by a partition, a, that 

 does not reach quite to the bot- 

 tom. The largest of these divisions, 

 b, is half filled with layers of sand 

 of different degrees of coarseness, and into this the water 

 10 be filtered is put ; in passing down through the sand, 

 all the mechanical impurities are detained, and it rises 

 into the other division, c, perfectly clear. This method 

 is so simple, that it may be practiced anywhere without 

 difficulty. The shape and size of the cistern are quite 

 immaterial. If a cock is placed in the smaller division 

 to draw off the water, it should be fixed a little way above 

 the bottom, lest there might be some J ight sediment 

 which would be disturbed. It is obvious that the sand 



