PHYSICAL AND CHEMICAL EXAMINATION OF MILK 



167 



Babcock test gives perfectly reliable results when it is executed 

 with care. 



Testing Cream by the Babcock Method.— The fat content of 

 cream can be tested by the Babcock method, but special care is 

 required to obtain reliable results. Since the specific gravity 

 of cream is lower than that of milk, a 17.6-c.c. pipet will not deliver 

 18 grams of cream and the result will be too low. The determina- 

 tion is further complicated by the varying viscosity of cream. If 

 cream has a high viscosity an appreciable amount will adhere to 

 the glass of the pipet, and as air-bubbles are generally present in 

 cream and tend to rise slowly, the real amount of cream falls short 

 of the required 18 grams. Washing the adhering cream out of the 

 pipet with water corrects the error in a measure, but a true charge 

 can only be obtained by weighing. 



Farrington and Woll have determined the weight of cream of 

 different fat content delivered from a 17.6-c.c. pipet when the cream 

 is fresh from a separator. The figm-es are given in the following 

 table : 



WEIGHT OF FRESH SEPARATOR CREAM DELIVERED FROM A 17.6-C.C. PIPET 



When corrections are made according to these figures good re- 

 sults are obtained only when the cream is fresh from the separator. 

 After it has stood for some time conditions change with the in- 

 creasing acidity. Bacterial activity not only increases the acidity of 

 the cream, but produces gas-bubbles, which are held in suspension 

 and decrease the specific gravity of cream. Whenever possible 

 cream samples should be weighed. Special balances can be pro- 

 cured for this purpose on which one or more bottles can be weighed 

 and which remain sensitive if properly cared for. The bearings, 

 if made of iron, must be kept free from rust. (See Figs. 52 and 53). 



Cream Test Bottles. — Special test bottles have been designed 

 for cream testing, since milk bottles record only 8 to 10 per cent, 

 fat (Fig. 63). The necks of cream testing bottles are devised to 

 hold more than 10 per cent. fat. Either a bulb is blown in the 



