268 THE CHEMICAL ANALYSIS OF BUTTER FAT. 



with the acid to be used in a small bottle, and a 5 c.c. pipette, 

 are placed in an incubator kept at 30 C. for at least half an 

 hour, and the temperature noted. Five c.c. of acid are added, and 

 the mixture stirred well with the thermometer, till the tempera- 

 ture ceases to rise. The difference between the initial tempera- 

 ture and that finally attained is taken as the rise of temperature, 

 and the Relative Molecular Maumene figure is calculated from 

 this. 



The R.M.M. of butters varies from 33-0 to 34-5, with a mean 



value of 34-0. The ratio . ^'. M ' M ' ~ *, has been about 0-633, 



iodine absorbed 



varying from 0-615 to 0-649. Any increase in this ratio may 

 be taken to indicate adulteration by vegetable oils. 



This method is occasionally useful, but is rather troublesome, 

 and cannot be well recommended, except as an additional test in 

 cases of doubt. It is very important that the fat be dried well. 



Detection of Rancidity in Butter. The amount of free 



fatty acids in fresh butter does not exceed 5 c.c. - acid per 100 



grammes, any higher figure indicates partial hydrolysis. Soltsien 

 recommends that the fat be steam distilled, treated with alkali 

 in excess, and again steam distilled. Wellmann's reagent * is 

 added to the distillate, and ammonia in excess ; and a blue 

 colouration in from half to one minute indicates rancidity. 



* Five grammes of molybdic acid is saturated with sodium carbonate 

 solution, 1 gramme of sodium phosphate is added, and the solution 

 evaporated to dryness, and fused. The mass is dissolved in boiling water, 

 and concentrated nitric acid (5 to 7 c.c.) .added till the yellow shade is 

 permanent, and the solution made up to 100 c.c. 



