78 PUBLIC HEALTH CHEMISTRY 



and bring to the boil, and just keep boiling. Now add the 

 whey from the burette until all the blue colour is discharged. 

 The end reaction is difficult. Allow to settle, place a drop 

 of supernatant liquid on a white tile, add a drop of K 4 FeCy 6 , 

 and then a drop of acetic acid. A brown precipitate shows 

 that some copper is still unreduced. 



Read the amount of whey added, divide by 10. This 

 gives the amount of milk which exactly reduces 10 c.c. of 

 Fehling's solution. But 10 c.c. of Fehling's solution are 

 reduced by 0-0667 S rm - f lactose, so that this quantity 

 of milk contains 0-0667 S rm - f lactose, and the amount 

 in 100 c.c. and 100 grm. is readily calculated. 



Fehling's Solution : synonyms, potassio-cupric tartrate 

 solution, or alkaline cupric tartrate solution consists of 

 34-65 grm. of crystallized copper sulphate, CuSO 4 '5H 2 O, 

 176 grm. of Rochelle salt, KNaC 4 H 4 O 6 -4H 2 O, 77 grm. 

 sodium hydrate, NaOH, dissolved in water and bulk made 

 up to 1000 c.c. Of this solution 10 c.c. are completely 

 reduced by 0-05 grm. of glucose, laevulose, or invert sugar. 

 Fehling's solution does not keep well, and so it is often 

 made up in two parts, equal measures of which produce, 

 when mixed, Fehling's solution. Solution No. i : 34-64 

 grm. of copper sulphate crystals dissolved in water, 0-5 c.c. 

 sulphuric acid added, and bulk made up with water to 500 

 c.c. Solution No. 2 : 176 grm. Rochelle salt and 77 grm. 

 caustic soda dissolved in water, and bulk made up to 500 c.c. 



Cane Sugar in Milk. (Present in preserved milks, 

 but here described for completeness.) Take a portion of 

 the whey from the above process, and boil it with i c.c. 

 of strong HC1. Cool and neutralize with anhydrous sod. 

 carb., and make up bulk originally taken to three times 

 with distilled water. Estimate the invert sugar produced 

 as for lactose. Subtract the percentage of lactose pre- 

 viously found from the percentage of invert sugar now 

 obtained, and the remainder is the amount of invert sugar 

 derived from cane sugar. This multiplied by 0-95 gives the 

 percentage of cane sugar present. 



Nitrogen in Milk Is the most constant ingredient, 

 and never falls below 0-5 per cent. Ten grams, of milk 

 are weighed into a dry Kjeldahl flask. Evaporate to dry- 

 ness on the water bath, and to the dried residue add 20 c.c. 



