BUTTER 91 



fat almost as soon as melted, while with process 

 butter the fat may remain turbid for a long while. 

 When the curd has largely settled, as much of the 

 fat is poured off as possible, and the remaining 

 mixture is thrown on a wet filter, by which the 

 water will drain away, carrying the soluble 

 proteins and salt. A few drops of acetic acid 

 are added to the filtrate and the mixture is 

 boiled. The filtrate from ordinary butter gives 

 a slight milkiness, but that from process butter 

 gives a flocculent precipitate. Quantitative ex- 

 amination is made by dissolving 50 grams of the 

 sample in ether; if it is ordinary butter, the curd 

 is so finely divided that it remains suspended for 

 some time. As much as possible of the solution 

 is decanted and the mass transferred to a sepa- 

 rator, the casein, water, and salt removed, and the 

 remainder washed three times, at least, with 

 ether to remove the fat. The curd is collected 

 on a filter, washed with water, and the nitrogen 

 determined by treating the precipitate with the 

 filter by the Kjeldahl-Gunning method. The 

 filtrate from the curd is made slightly acid with 

 acetic acid, boiled, the precipitated proteins 

 collected on a filter, and the total nitrogen de- 

 termined. The factor 6.38. may be used in each 

 case for converting the nitrogen into proteins. 



A distinction between ordinary and process 

 butter may often be made by microscopic ex- 



