122 



Testing Milk and Its Products. 



134. Manns' testing outfit. The appa- 

 ratus (see fig. 41) and chemicals needed for 

 testing the acidity of milk or cream by the 

 so-called Manns ' test include one gallon of a 

 one-tenth normal alkali solution; four ounces 

 of an alcoholic solution of phenolphtalein, a 

 50 cc. glass burette provided with a pinch- 

 cock, a burette stand, and a pipette for meas- 

 uring the sample. This outfit will make about 

 100 tests and is sold for $5.00. 1 



135. The alkaline tablet test. Solid 

 alkaline tablets were proposed by Far- 

 rington in 1894, as a substitute for the 

 liquid used in the Manns ' test. 2 It was 

 found possible to mix a solid alkali car- 

 bonate and coloring matter, and com- 

 press the mixture into a small tablet, 

 which would contain an exact amount 

 of alkali. The advantage of the tablets 

 lies in the fact that they will keep far 



better than a standard alkali solu- 

 tion, and they can be easily and 

 safely sent by mail; they also re- 

 4uire less apparatus and are con- 

 FlG 'tnMtnnt' ra t t est s . used siderably cheaper than standard 

 alkali solutions; 1000 of these tablets, costing $2 00, will 



solution is diluted to 1850 cc. in a two-quart bottle, such as is used for 

 mineral waters. Each cc. of this solution represents .01 cc. of acidity 

 when 17.6 cc. of cream is measured off. The titration is made in tin' 

 usual manner, using phenolphtalein as an indicator. 



1 Devarda's acidimetcr (Milch/eitung, 1896, p. 785) is based on tin- 

 s;nno principle as Manns' t i st: one-tenth soda solution is added to 100 

 cc. of milk in :i glass-stoppered graduated flask, 2 cc. of a 4 per cent, 

 phenolphtalein solution being used as an indicator. The graduations 

 on the neck of the flask give the "degrees acidity" directly. 



2 Illinois exp, riinont station, bulletin 32, April, 1894. 



