YIELD AND COST OF CULTIVATION. 205 



the exact percentage or degrees is doubled. This will 

 give the so-called " quotient de purete."^ As a general 

 thing it may be said that the amount of solids indicated 

 by the areometer is greater than the reality, on account 

 of various decompositions that have taken place in the 

 juice, and for that reason it has been argued that a 

 given amount of juice should be evaporated and the re- 

 maining deposits weighed. But even then small errors 

 will exist. Too much reliance cannot be placed upon 

 the percentage of these, as the manufacturer will 

 greatly suifer from it. For example, the greater the 

 mineral salts the greater the amount of bone black 

 required in the manufacture ; this increasing the ex- 

 pense, w^hich would be a small item if the foreign 

 elements could all be gotten rid of, but unfortunately 

 these seem still to remain in the juice, and, in a remark- 

 able degree, prevent the crystallization. Bad results 

 may also be expected from the nitric albuminous 

 substances, and it is important to know what these are 

 and to what extent they exist. The effect produced 

 by tannin has been before mentioned, and a most in- 

 genious method has been proposed by Mr. Walkhoff^ 

 for its detection. 



' Mr. WalkhofFindorses this principle emphatically on account of its simplicity 

 and calls attention to the fact that a solution of pure sugar at a density of 1.0488 

 will indicate 50° with the polariscope. which, when doubled, will represent 100 

 per cent, of pure. 



2 A solution of 100 grammes of water and 1 gramme of pure tannin, or, 

 again, 10 grammes of tannin to 1000 grammes of water, 10 c. c. of juice ai'e 

 united with 100 c. c. of water and 10 of a solution of alum, the total is heated 



