PREPARATION OF BUTTER FAT FOR ANALYSIS. 



315 



vessel. It is sometimes of importance to prepare the butter 

 free from water. This may be done by shaking it with a little 

 calcium chloride (free from hme) and filtering again. Chatta- 

 way proposes to remove the water by stirring in a number of 

 pellets of filter-paper, which have been dried in the water-oven. 

 The author has found that, as far as the proportions of the vola- 

 tile acids, insoluble acids and saponification equivalent are 

 concerned, the fat is entirely unafiected by this treatment, though 

 certain properties — e.g., rise of temperature with sulphuric acid 

 — are slightly afiected, owing to removal of the water. 



After filtration, the fat is rapidly cooled, so as to prevent 

 partial solidification and to ensure the homogeneous nature of 

 the sample. 



Stokes' Fat-clearing Process. — Stokes uses a tube open 

 at both ends (Fig. 41), the smaller and lower of 

 which is closed 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 transferred to a 

 centrifuge (800 to 900 revolutions per minute).* 

 The casein and water are driven into the narrow 

 end and read oS. The result is taken as all water. 

 (This is used to sort out butters which come for 

 water determination, and is not absolutely corn^tt 

 if checked by gravimetric methods.) Into the hot 

 fat a wad of cotton wool is placed, and is slowly 

 forced down by a wire (see Fig. 41), so as to 

 prevent any cloudy particle from oozing up. The 

 fat thus obtained (above the pad) is perfectly '^ 



clear, practically dry, and ready for use. ^fr 



Recapitulation of Properties. — The following j-jg, 41 

 recapitulation of the essential difierences between stokes' Butter 

 butter fat and other fats likely to be used as Clearing Tube, 

 substitutes or for adulteration wUl serve to 

 show the basis of the methods employed in the anahsis 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 but}Tic acid, but 

 the whole of the members of the series C„Hiu+iCOOH, in which 

 n is an odd number from 3 to 17, are present ui 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 meinbers 

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

 * Gerber disc is quite sufficient. 



