168 THE ESTIMATION OF SUGARS. 



He also, at the author's suggestion, has wcrked out the following 

 method, which avoids the calculation ; add to 100 c.c. of diluted 

 condensed milk 



(a) 10-25 c.c. of water, 



(b) a number of c.c. equal to W X F X 1-08, 



(c) 3 c.c. of acid mercuric nitrate ; 



polarise, and calculate the reading due to cane sugar as before. 

 Then the difference between the reading before inversion 



100 



and that due to cane sugar multiplied by -^ will give the per- 

 centage of milk-sugar, and the reading due to cane sugar multi- 



100 



plied by w will give the percentage of cane sugar. 

 1 * 2i VV 



Revis and Payne point out that the acid commences to invert 

 the cane sugar at once, and give a formula which corrects for this 

 as well as for the error due to incomplete removal of proteins ; 

 if 141-71 be substituted for 142-66 and the milk-sugar be divided 

 by I'Ol, the formulae above will become essentially those of 

 Revis and Payne. 



The fat may be estimated by a rapid method, as the deviation 

 from the truth due to an error in the fat estimation of 0-5 per 

 cent, is only 0-1 per cent, in the cane sugar ; the possible error 

 due to the use of the simplified method does not exceed 0-2 

 per cent. Richardson and JafTe have proposed a somewhat 

 similar method, but invert and polarise at 86, at which tem- 

 perature inverted cane sugar reads ; the method is, however, 

 less convenient than that of Harrison. 



The addition of phospho-tungstic acid to the acid mercuric 

 nitrate filtrate (p. 106), gives slightly higher and more correct 

 results, and should not be neglected with condensed milk. 



Knight and FormanSk, bearing in mind the author's observa- 

 tion that mercuric nitrate does not remove all proteins, add 

 1-7 c.c. of 5 per cent, phospho-tungstic acid for each 10 grammes 

 of condensed milk, and then, after shaking, 2-1 c.c. of 25 per 

 cent, neutral lead acetate for each 10 grammes. After shaking 

 and filtering, potassium oxalate crystals are added until a curdy 

 precipitate forms, which settles quickly. They polarise directly, 

 and, after inversion by HC1, at room temperature. 



Other Methods. An approximation to the percentage of 

 cane sugar can be obtained by determining the total polarisation 

 and deducing the milk-sugar by multiplying the ash by 6-5, or 

 the aldehyde figure by 0-24. This method serves for controlling 

 the preparation of condensed milk, but is of course only of 

 approximate accuracy. 



Another method, which gives fair approximate results, is to 



