DAIRY HUSBANDRY 
51 
EXERCISE NO. 37 
Object: To become acquainted, with Walker’s Formaldehyde solution method 
of casein determination. 
Procedure: It is important that the formaldehyde used in this test be 
neutralized with alkali before using; i. e., it must have a dis¬ 
tinct pink color to show that it is neutralized. 
A. Test each of the lots of milk provided in duplicate as follows: 
(1) Pipette 10 cc. of a well mixed sample of milk into a porce¬ 
lain cup, add 1 cc. of a one per cent solution of phenolphta- 
lein; neutralize with an n / 9 NaOH solution, stirring con¬ 
stantly until a fairly permanent deep pink color develops. 
(2) Add 2—3 cc. of natural 40% formaldehyde. 
(3) Titrate with n / 9 NaOH solution until the same permanent 
deep color develops as before adding the neutral formalde¬ 
hyde. 
(4) The number of cc. n / 9 NaOH solution used for step 3 mul¬ 
tiplied by 1.63 will give the per cent casein in the sample. 
B. Make a fat test of the milk provided and compare the ratio of 
the casein to the fat. 
Observations: 
Sample 
% casein 
% fat 
Ratio 1 : ? 
l 
2 
Conclusions: 
Questions: (1) If you assume that 17.5 cc. of milk was used instead of 10 
cc. what factor would you use? 
(2) What factor would you use if you have an n /i 0 normal solution 
instead ol an n / 9 solution? 
(3) How may casein be prepared commercially? 
(4) What chemicals are used for precipitating casein? 
References: F. & W. IT 18. 
