310 MILK AND CREAM TESTING 



one test over to the next. In going from a high testing sample 

 to a low testing sample one may easily cause the reading of the 

 low test sample to be one- or even two-tenths per cent too high. 



Adding Acid. — Carefully measure out acid (temperature 

 55 to 65 degrees) into the acid measure. A quantity exactly 

 to the scratch on the little cylinder will be required if the acid is 

 the right strength and temperature, and the milk is not too 

 warm. Warm acid or a warm sample increases the chemical 

 action and will cause a burning of the sample unless checked. 

 If either is too warm use slightly less acid. Pour the acid 

 carefully down the side of the neck, allowing the heavy, half- 

 sticky substance to flow under the milk rather than through it. 

 If poured directly downward into the sample burning and un- 

 reliable reading are almost certain to follow. 



Mixing Acid and Milk.— By one not especially familiar 

 with the process this mixing should he done immediately after 

 the acid has been added and by all means should be finished 

 quickly when once started. Care should he taken not to shake 

 the sample violently, nor in a perpendicular direction, since this 

 would throw a mass of coagulated milk into the neck of the 

 bottle where it would be forced out by the heat and lost, thus 

 invalidating the whole sample. Shake the sample with an 

 elliptical, rotary motion in such a way as to mix the contents 

 of the bottle without throwing any of it into the neck. Observe 

 the sample for an instant to note the color. Allow it to con- 

 tinue the chemical action till a strong coffee color or deep cherry 

 red has been reached. If the acid is too strong or the ingredients 

 at such a temperature that the mixture at this point begins to 

 turn black, 2 or 3 c.c, a teaspoonful of lukewarm water should 

 be added and then mixed. This checks the action of the acid 

 and prevents charring. Care to get both milk and acid to the 

 favorable temperature will be time well spent, for half the secret 

 of making good tests is in getting the right temperatures. 



Whirling. — When all the samples to be tested at one time 

 have been gotten ready in manner just described, the bottles are 

 to he placed in the centrifugal machine, taking care to balance 

 the load in all cases. Increase the speed gradually until the 



