DAIRY PRODUCTS. 53 



REFRACTIVE INDEX OF OILS. 



The use of the re f IMC to meter of Abbe in the examination of butters 

 has been proposed by Miiller. 1 The principle of the use of this instru- 

 ment is, that the fats of pure butter possess a less refractive power 

 than the glyccrides of a higher molecular weight. 



This subject lias also been treated by Skalweit. 2 



ESTIMATION OF SOLUBLE ACIDS IN BUTTER FATS. 



fltcthod of Heliner and Angell. 3 Hehner and Augell, in June, 1874, pub- 

 lished a pamphlet on butter analysis in which the details of their method 

 were given. 



The following is an abstract of this method : 4 



A weighed quantity, usually 3 grams, of the fat was saponified in a 

 porcelain dish with caustic potash, with frequent stirrings with a glass 

 rod. The clear butter soap was transferred to a flask or retort and 

 decomposed by means of dilute sulphuric acid. This mixture, which 

 contained sulphate of potash, glycerine, and the volatile acids in solu- 

 tion and the insoluble fatty acids floating on the top, was distilled, and 

 the acidity of the distillate estimated by means of a soda solution of 

 known strength. The practical difficulties of this method, such as the 

 violent bumping of the boiling liquid and the impossibility of obtain- 

 ing a distillate perfectly free from acid, led the authors to adopt a 

 somewhat different method. 



This modification is based upon the different percentages of the 

 insoluble fatty acids in butter and other animal fats. The insoluble 

 acids, after saponiflcation, were collected on a moistened filter paper, 

 washed with hot water, and when the soluble acid was washed out, 

 dried and weighed. 



They found the percentage of insoluble fats in butter to vary from 

 85.40 to 86.20, while in other animal fats the percentage of insoluble 

 fatty acids was about 95.5. As will be shown further along, a small 

 error is introduced into this method by washing the insoluble fatty 

 acids on the filter. When this error is avoided, it is found that the per- 

 centage of the insoluble fatty acids in butter fat is considerably higher 

 than the figure which has just been given. A detailed description of 

 this part of the process will be given farther on. Turner 5 suggested 

 the employment of alcohol, with the view to hasten the saponification 

 of I he fat; a modification of the process which has been almost uni- 

 versally adopted by analysts. 



About 30 or 40cr. of spirits of wine are added to the butter in the por- 

 celain dish and heated over the water bath to near the boiling-point. 



1 Arcliiv (1. Pliann., 1886, p. 210. 

 2 Rep. d. Vcr. Anal., Chcm., 1888, p. 181. 

 3 Analyst, 1877, p. 147. 



^Hassall, Food and its adulterations, p. 446. 

 5 Ibid, p. 447. 



