ESTIMATIOX OF MILK-SUGAR. 93 



Vieth Method. — Vieth, when using the small Mitscherlich 

 half-shadow polariscope made by Schmidt and Hcensch, prefers 

 to add the stronger mercuric nitrate solution, described above, 

 direct to the milk, and to polarise the resulting filtrate. He 

 finds the volume of precipitated proteins from 100 c.c. of milk- 

 to amount on the average to 3 c.c, and, consequently, adds 

 3 c.c. of acid mercuric nitrate solution to allow for this. The 

 method is carried out as follows : — Measure 50 c.c. of milk into 

 a small flask, add 1'5 c.c. of acid mercuric nitrate, and well mix 

 by shaking violently ; pour the mixture on to a filter, and fill a 

 polarimeter tube with the filtrate ; polarise, and correct the 

 reading for that obtained in a blank reading — i.e., by reading a 

 tul)c filled with water. 



jVs the [«]i, of milk-sugar is 0:2 -5 , the reading, if in angular 

 degrees, can be converted into percentages of milk-sugar by the 

 following formula — 



100 100 



Where- m - minilin of grammes of niilk-sugar por 100 c.o. of solution 

 polarised. 



I = length of tube in millinieti'fs. 



r -~ rcatlini;' in nni^nlar dcgreos. 



If a tube of 198 ••! millimotvos be used (these tubes are sup- 

 plied with the instrument used by Vieth), the formula becomes 



'" = l-d42- 

 If the length of the tube be '200 millimetres, the formula is 



1-O.V 



The resulting figure representing milk-susar in the solution 

 polarised must be submitted to correetion. 



The volume of the liquid from which the fat and protein have 

 been precipitated is the volume of the milk plus that of the 

 mercuric nitrate miinifi that of the protein precipitate and fat. 



.\s the volume of the mercuric nitrate was purposely made 

 equal to that of the protein, both of these may be neglected, one 

 compensating for the other. 



Taking the volume of the milk as 100 c.c, the volume of fat 

 in this will be the percentage by weight of fat multiplied by the 

 specific gravity of the milk, divided by the specific gravity of 

 the fat. 



The milk-sugar may be either calculated as hydrated or 

 anhydrous sugar, but it is usual to calculate it in milk analysis as 

 anhvdrous sugar. 



