RECAPITULATION OF PROPERTIES. 241 



with a rubber plug. The lower divisions each represent 1 per 

 cent. For butter it is used thus : 



The butter is put in it (as the tube stands immersed in boiling 

 water) up to the 15 c.c. mark, and when melted the tube is trans- 

 ferred to a centrifuge (800 to 900 revolutions per minute).* 

 The casein and water are driven into the narrow end and read 

 off. The result is taken as all water. (This is used to sort out 

 butters which come for water determination, and is not absolutely 

 correct if checked by gravimetric methods.) Into the hot fat 

 a wad of cotton wool is placed, which is slowly forced down by 

 a wire, so as to prevent any cloudy particle from oozing up. 

 The fat thus obtained (above the wad) is perfectly clear, practi- 

 cally dry, and ready for use. 



Recapitulation of Properties. The following recapitula- 

 tion of the essential differences between butter fat and other 

 fats likely to be used as substitutes or for adulteration will serve to 

 show the basis of the methods employed in the analysis of 

 butter. Butter fat is characterised by the presence, in con- 

 siderable amount, of glycerides of the fatty acids of low molecular 

 weight. The lowest and most important is butyric acid, but 

 the whole of the members of the series C n H 2n+1 COOH, in which 

 n is an odd number from 3 to 17, are present in butter fat. A 

 considerable amount of acids of the oleic series, of which not 

 much is known, is also present ; of this series, the lower members 

 are certainly absent, and the unsaturated acids are of a higher 

 mean molecular weight than the saturated acids : it is probable 

 that oleic acid is the chief representative of the series, and, 

 possibly, higher homologues occur. It is not known with cer- 

 tainty whether acids of other series occur in butter fat. The 

 alcohol present is almost entirely glycerol. 



The pioneer in butter analysis was Otto Hehner, who demon- 

 strated in 1872 that upwards of 5 per cent, of the fatty acids 

 were volatile, and that the quantity of insoluble fatty acids was 

 very much less than that yielded by nearly all other fats. The 

 bulk of the methods at present in use are the legitimate outcome 

 of Hehner's work. Perhaps the only method which is not 

 derived from the first investigation of Hehner is that of von 

 Hiibl, who showed that, by the action of an alcoholic solution 

 of iodine and mercuric chloride, a quantitative addition of halogen 

 could be made to unsaturated glycerides, but in the simplification 

 of this method Hehner has had a large share. 



Estimation of Volatile Fatty Acids. 

 Reichert Process. Hehner and Angell, after showing that 

 butter contained more butyric acid than was (then) generally 



* Gerber disc is quite sufficient. 



16 



