XVI. THE ANALYSIS OF MILK AND MILK PKODUCTS 357 



detsrmin'ng the amount of alkali necessary for saponification of a fixed 

 quantity of the fat, or what is practically its reciprocal, the " saponifi- 

 cation equivalent," i.e., the weight of fat corresponding to the gramme 

 equivalent of the alkali. The saponification equivalent of butter, in con- 

 S3quence of the low molecular weights of the acids which it contains, 

 is much smaller than that of most other fats, the actual values found 

 being about 247 for genuine butter and about 288 for most other fats. 

 For other methods the reader must refer to some manual of analysis. 



Butter Colouring. The natural colouring matter of milk is ap- 

 parently contained in the fat and is subject to considerable variation. 

 The amount is usually least in winter, and, at that season, butter is 

 often white in colour. It is a common practice to add some colour- 

 ing substance to the cream in the churn, so that the colour of the 

 butter may be deeper. The usual addition is annatto, a colouring 

 matter obtained from the seeds of Bixa orellana. 



The colouring substance is soluble in alkaline solutions and in oils. 

 The commercial solution generally contains sodium carbonate. Other 

 colouring matters, e.g., carrot juice, turmeric, saffron, marigold and 

 even chrome yellow (lead chromate) have been occasionally used. The 

 last mentioned is highly objectionable and poisonous. Its presence 

 would be indicated by the occurrence of lead and chromium in the 

 ash. Annatto can be detected by taking about 5 grammes of butter, 

 dissolving it in about 50 c.c. of ether, and then shaking vigorously with 

 about 15 c.c. of very dilute caustic soda. The whole is set aside, when 

 it separates into two layers, the upper one consisting of an ethereal 

 solution of fat, the lower containing the annatto, if present. Some of 

 the lower liquid is then removed, evaporated to dryness, and the 

 yellow residue treated with a drop of strong sulphuric acid. If an- 

 natto be present a blue or violet colour is produced, quickly changing 

 to green, and finally to a brownish hue. Another way of separating 

 artificial colouring matter from butter is due to Martin. A mixture 

 of about 2 parts of carbon disulphide and 15 of alcohol is made, and 

 five grammes of butter are treated with 25 c.c. of this liquid and the 

 whole well shaken. On standing, the carbon disulphide, with the fat, 

 sinks to the bottom, and the colouring substances remain in the alcohol. 



CHEESE. In cheese, the usual constituents determined in an 

 analysis are water, ash, fat and casein, and although the last mentioned 

 is the characteristic ingredient, the value of a sample depends far more 

 upon the amount of fat which it contains than upon its casein content. 



Water is determined by heating about 5 grammes of the sample, in 

 thin slices, in a weighed dish containing some asbestos, which serves 

 to absorb the melted fat. The heating should be done in a steam oven 

 and extend over at least ten or twelve hours. The loss in weight gives 

 the water. 



Ash. The residue from the previous determination is set on fire, 

 when the asbestos will act as a wick, from which the fat will burn . 

 The dish is then heated to a low redness until the black carbon particles 

 disappear. 



