74 FOODS AND FOOD ADULTERANTS. 



volume of the wasli water amounts to 250 to 500cc. By this time all 

 the salt has been dissolved and separated from the butter. 



Chromate of potassium is now added to the salt solution, and the titra- 

 tion is accomplished by a standard silver nitrate solution. 



The amount of NaOl in butter is also determined by dissolving the fat 

 with ether or light petroleum, and after incineration of the curd, 

 weighing the residual ash, which is taken as the amount of salt present. 

 This method is not to be recommended since it includes the salt found 

 in the other mineral constituents. 



Sell 1 gives the following method : Ten grams of butter are weighed 

 into a porcelain crucible and dried at 100 0. for six hours. The melted 

 fat, &c., is now filtered, and crucible and filter are washed with ether. 

 The filter with its contents is then incinerated. The ash is extracted 

 with water, filtered, and the NaCl estimated volumetricaily in the fil- 

 trate. 



ESTIMATION OF CURD. 



The methods of estimating curd depend on the principle of first dry- 

 ing a weighed portion of the butter, and afterwards extracting the fat 

 with ether or petroleum. The residual mass is then weighed and the 

 curd determined by loss on ignition. This process is carried on in this 

 laboratory as follows : 



Five to ten grams of butter are dried at 100 C. for a few hours in a 

 porcelain dish. The dried fat, &c., are filtered through a Gooch cruci- 

 cle, the contents of the dish all brought into the crucible and well 

 washed with ether or light petroleum. The filter crucible is dried for 

 two hours and weighed. The curd is then determined by loss of 

 weight on ignition. A number of experiments have also been made 

 to convert the curd directly into an ammonium compound by Kjel- 

 dahl's process. This method has not met with sufficient success to 

 merit a recommendation to general use. This method was first tried in 

 the laboratory in 1884. 



Babcock finds this method more satisfactory. 2 Ten grams of the fat 

 are treated with light petroleum, and after the fat solution has been de- 

 canted the treatment is repeated. The purified curd is then treated by 

 KjeldahPs process. 



QUALITATIVE TESTS. 



The qualitative tests employed in the detection of artificial butter 

 are the following : 



(1) Microscopic examination. This method has already been suffi- 

 ciently described. 



(2) Solubility in a mixture of am} 1-alcohol and ether. 



1 Op tit, p. 5^7. 



2 Fifth Ann. Rept. Bd. Control N. Y. Exp. Sta., p. 335. 



