ESTIMATION OF CANE SUGAE. 101 



The solution is brought to boiling, and the sugar solution run 

 in gradually, till the blue colour of the liquid is destroyed, the 

 boiling being maintained the whole time, and the sugar solution 

 run in slowly towards the end. 



As the reaction takes place somewhat slowly, boiling must be 

 continued for a few minutes before it can be finally decided that 

 the blue colour is permanent. 



It is necessary to repeat the titration, adding a little less of 

 the solution, as with Fehling's solution. This may be advan- 

 tageously added all at once, and the boiling continued for five 

 minutes. If the boiling be unduly prolonged, the ammonia may 

 be boiled off, and cuprous oxide will then begin to deposit : in 

 order to avoid this, Shenstone places a tapped funnel in the 

 cork, by means of which an addition of strong ammonia can be 

 made if necessary. 



Stokes and Bodmer strongly recommend this method, and 

 state that the reducing power of milk-sugar is 52 per cent, of 

 that of glucose — i.e., 100 c.c. of Pavy solution = (ro'.iGl gramme 

 of milk-sugar. 



It is advisable to standardise the Pavy's solution on a solution 

 of pure milk-sugar containing 0"5 gramme per 100 c.c. 



Heliiier has shown that by varying the proportion of suits in 

 solution, such as alkaline tartrates and carbonates, the acciu'acy 

 of the results is affected; but by standardising the solution at 

 the time of using with a solution of pure milk-sugar, the elTect 

 of any such variations is eliminateil. 



Allen has modified the procedure by placing a layer of petro- 

 leum over the Pavy solution, and dispensing with the cork. 

 This enables an ordinary burette, or even pipette, to be used. 



Estimation of Cane Sugar in Milk. — Cane sugar is sometimes 

 added as an adulterant of milk, but the determination is more 

 often required in the case of condensed milks. 



.\.n approximate estimation may be made by estimating the 

 sugar by precipitation with alcohol, and the milk-sugar by 

 Fehling or Pavy solution ; the difference between the two will 

 not be far from the cane sugar. 



Muter Method. — iluter estimates as follows : 10 grammes 

 of milk are evaporated to dryness on -1 grammes of hydrated 

 calcium sulphate with frequent stirring, so that nothing sticks 

 to the basin. The dry residue is powdered, placed in a dried 

 filter, and extracted with ether in a Soxhlet apparatus. The 

 residue, together with the filter, is transferred to a beaker, 

 •Jt) c.c. of hot (not boiling) water added, and the whole well 

 stirred ; 30 c.c. of rectified spirit (60" overproof, sp. gr. 0'825) 

 are then added, and the mixture allowed to cool, stirring occa- 

 sionally. When cool, it is thrown on a filter and washed with 



