360 THE ANALYSIS OF MILK AND MILK PRODUCTS. XV. 



in oils. The commercial solution generally contains sodium 

 carbonate. Other colouring matters, e.g., carrot juice, tur- 

 meric, saffron, marigold, and even chrome yellow (lead chro 

 mate) 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 contain- 

 ing 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 annatto 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 5 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 10 or 

 12 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 low redness until the 

 black carbon particles disappear. 



