17,2 Adriano: Determination of Lactose 215 
the same paper a picrate colorimetric method for lactose is de- 
scribed which is materially simpler than the one given by Dehn 
and Hartman. (2) Parallel results obtained with the colorimet- 
ric method of Folin and Denis and the titration method are 
given to show that the latter is the more accurate. 
MATERIALS AND PROCEDURE 
QUISUMBING’S(7) method as applied to the determination of lactose in 
MILK 
Place in an Erlenmeyer flask 50 cubic centimeters of 0.1 N 
potassium permanganate solution, 25 cubic centimeters of a 
solution of sodium carbonate containing 8.48 grams of (anhy- 
drous) sodium carbonate per liter and 5 or 10 cubic centimeters 
of the filtrate obtained as indicated below. Add sufficient wa- 
ter to make the final volume of the mixture 100 cubic centi- 
meters. Heat the mixture on the heating device, consisting of 
an iron tripod with asbestos hood, with the heating power so 
regulated that its temperature is raised from 29° C. to 95° C. in 
two minutes, and continue heating for another two minutes 
after the temperature has reached 95° C. Remove the flask and 
add gradually 25 cubic centimeters of 30 per cent sulphuric acid 
and 0.1 A oxalic acid solution until the liquid is clear. Titrate 
the excess of oxalic acid against standard 0.1 N potassium per- 
manganate solution, adding the latter until the liquid assumes 
a pink color that remains for a few seconds. The sum of the 
number of cubic centimeters of 0.1 N potassium permanganate 
solution used in oxidation and in titration minus the number of 
cubic centimeters of 0.1 N oxalic acid solution gives the num- 
ber of cubic centimeters of 0.1 N potassium permanganate 
solution that is actually used in oxidation The corresponding 
lactose value with the use of pure lactose is shown in Table 2. 
The pure lactose used in obtaining the data for this table was 
prepared as follows: 
To an alcoholic solution, saturated at 40° C. of chemically 
pure lactose obtained from a local dealer, absolute alcohol and 
ether were added, and the sugar was allowed to crystallize 
from the solution in a vacuum desiccator over sulphuric acid. 
When about half of the solvent had evaporated, the crystals 
were separated from the mother liquor by suction and then 
washed with small amounts of ether and absolute alcohol. The 
lactose was recrystallized three times in the manner described 
and the purified product dried for sixteen hours at 40° C. under 
