THE ANALYSIS OF BUTTER 



75 



Estimation of Iodine Absorption. Weigh about 

 0.4 to 0.5 gramme of fat in a stoppered bottle, dis- 

 solve in 10 c.c. of chloroform, and add 20 c.c. of 

 Wijs' iodine solution (see Appendix). At the same 

 time mix 10 c.c. of chloroform with 20 c.c. of iodine 

 solution, and place both bottles in a dark place for half 

 an hour. Add 15 c.c. of a 10 per cent, solution of potas- 

 sium iodide solution 

 to each, and about 

 200 c.c. of water, and 



titrate with - sodium 

 10 



thiosulphate solution 

 (see Appendix) till 

 the colour on shak- 

 ing is removed from 

 both aqueous and 

 chloroformic solu- 

 tions ; a little starch 

 solution may be 

 added when the colour 

 is very pale, and the 

 titration carried on 

 till all blue has disappeared, but its use is not absolutely 

 necessary. 



The number of c.c. of thiosulphate multiplied by the 

 value of i c.c. in terms of iodine used in the blank 

 experiment gives the total amount of iodine added to 

 the fat ; the number of c.c. of thiosulphate similarly 

 multiplied used in the actual experiment gives the 

 weight of iodine not absorbed by the fat, and the 

 difference between these two gives the quantity 

 absorbed, and this multiplied by 100 and divided by 

 the weight of fat taken is the iodine absorption. 



Determination of Refractive Index. The Zeiss 

 butyro-refractometer is employed for the determina- 

 tion of the refractive index ; it consists of two water- 

 jacketed prisms, between which the substance is 

 placed, a mirror to reflect light through these, an eye- 



FIG. 37. Margarine 



