58 A DAIRY LABORATORY GUIDE 



EXPLANATION OF EXERCISE XI 



In testing butter by the Babcock method, the 

 practice is sometimes followed of melting the 

 butter and then putting it into the test bottle 

 by means of the pipette. It is posssible to do 

 this sometimes and get accurate results, but 

 the tendency for fat and water to separate 

 makes it difficult to get accurate tests. 



Division b of experiment 2 illustrates how 

 readily the fat and water separate. In draw- 

 ing off the fat for this experiment, keep the 

 point of the pipette at the surface of the fat. 



Carbon dioxide acts toward an alkali like an 

 acid. We are told that some of the acidity 

 of the milk is due to the presence of C02. 

 In experiment 4, pouring the milk back and 

 forth from one vessel to another tends to mix 

 the CO2 of the air with the milk. Heat will 

 expel the CO2, and so after boiling the milk 

 the acid test would be lower than it would 

 be before boiling. This experiment also 

 shows that milk will take up gases. 



In the same way that acids and alkalies form 

 reactions so do solutions of certain salts form 

 reactions. When salts do react they follow 

 the same rule as acids and alkalies, namely, 

 that equal volumes of salts of the same chem- 

 ical strength will just neutralize one another. 

 This fact is made use of in determining, 

 quantitatively, the amount of salt (sodium 

 chloride) in butter. The salt used to neutral- 

 ize the sodium chloride is silver nitrate (Ag 

 N03) and the indicator used to tell when 

 enough silver nitrate has been added is a solu- 



