334 BUTTER. 



the flask gently rotated till the fat is dissolved ; 20 c.c. of the 

 iodine chloride solution is next added and the whole well mixed. 

 The flask is now put aside for half an hour. At the same time 

 one or more blanks — i.e., flasks containing 10 c.c. of carbon 

 tetrachloride and 20 c.c. of iodine chloride solution should be 

 put aside with the tests. 



After half an hour, 10 c.c. of potassium iodide solution are 

 added to each flask, and the contents are washed out into a 

 larger stoppered bottle with distilled water. The standard thio- 

 sulphate salutio]i is run in with continued shaking till only a 

 faint yellow colour remains ; a little starch paste is added, and 

 the thiosulphate solution run in, drop by drop, till the 'blue 

 colour disappears. The quantity of thiosulphate solution used 

 for the flask in which the sample was placed subtracted from 

 the mean of the blanks will give the equivalent of the iodine 

 Absorbed. This, multiplied by the strength of the solution, will 

 give the weight of iodine. By multiplying this by 100 and 

 dividing by the weight of fat, the percentage of iodine absorbed 

 is obtained. 



The following examples will make the mode of calculation 

 .clear : — 



Bxperimenl 1. Weight of fat taken, 0-i5006 gramme. 



Titrated with 26-48 o.c. of thiosulphate solution. 



„ 2. Weight of fat taken, 0-4991 gramme. 



Titrated with 26-55 c.c. of thiosidphate solution. 



Blank Xo. 1 took 43-35 „ „ „ 



„ 2 „ 43-45 „ 



Mean, 43-40 „ 



1 c.c. of the thiosulphate solution was equal to 0-001187 gramme of 



iodine. 

 Therefore 0-5006 gramme absorbed (43-40 — 26-48) X 0-001187 gramme 

 of iodine. 



= 0-2008 gramme or 40-11 per cent. 



= 0-4991 gramme absorbed {43-40 — 26-55) x 0-001187 gramme 



of iodine. 

 = 0-2000 gramme or 40-07 per cent. 



Bromine Absorption. — Instead of using the iodine chloride 

 solution, a solution of bromine in chloroform, or, what is far 

 preferable, carbon tetrachloride may be used. 



Four c.c. of dry bromine (this is best dried by shaking bromine 

 with anhydrous calcium chloride, decanting, and distilling from 

 .a small stoppered Wiirtz flask fitted with a good condenser) are 

 dissolved in 1 litre of dry chloroform or carbon tetrachloride. 

 The process is performed as above described, except that there 

 is no need to wait before titrating ; this may be performed at 

 once. 20 c.c. of the bromine solution are substituted for the 

 20 c.c. of iodine chloride solution. It is advisable also to increase 

 the amount of potassium iodide solution added to 20 c.c. or more. 



