IODINE VALUE 205 



which passes a calcium chloride tube, is heated on the 



water-bath until all is dissolved. 7-2 grams of finely 



powdered iodine are then dissolved in glacial acetic 



acid in a similar manner and added to the first solution. 



The mixture is then stoppered, allowed to cool, and 



made up to i litre with acetic acid. It is titrated after 



twenty-four hours as follows : — Ten or 20 c.c. of solution 



are mixed with 5 to 10 c.c. of potassium-iodide solution, 



diluted with 300 c.c. or so of distilled water, and titrated 



N 

 with — sodium-thiosulphate solution in the ordinary 



manner. The strength of the iodine-chloride solution 

 alters during the first twenty-four hours, but after that 

 will remain constant for several weeks. It must be 

 restandardised from time to time. 



Iodine Value Estimation. — About 0-75 gram of 

 butter-fat is dissolved in 10 c.c. of carbon tetrachloride, 

 and when dissolved 25 c.c. of the Wijs' solution is added 

 and the flask stoppered. After standing in the dark for 

 one to two hours the contents are washed into a conical 

 flask with water and mixed with 10 c.c. of KI solution, 

 the total volume being about 300 c.c. The residual 

 iodine is titrated with standard sodium thiosulphate. 



The calculation is made as previously described for 

 the Hubl method (13, p. 23). 



The Colour of Butter. 



Butter possesses naturally a light yellow colour, the deepness 

 of which depends on several causes. It is generally found that, 

 during the summer months when the cows are on grass, the colour 

 is deeper, while during the winter when the diet consists largely of 

 concentrated foods, together with hay, straw, and roots, butter 

 may be practically colourless. Again, the natural colour of 

 butter depends upon the breed of cow, the butter produced from 

 the milk of the Channel Islands breeds (Jersey, Guernsey) being 

 notably deeper in colour. It is the custom to colour butter artifi- 



