ii BUTTER 137 



About 10 g. butter are weighed out, together with a short 

 glass rod, into a porcelain dish, which is then heated over a 

 small flame, the butter being kept constantly stirred and the 

 flame regulated so that no fat spirts out. In this way all 

 the water is evaporated, and a point is reached where the 

 boiling stops suddenly and a fine foam forms on the surface, 

 whilst the casein at the bottom becomes a light brown colour. 

 As the water has then all been driven off, the flame is withdrawn. 

 Even though the heating should be continued a little too long, 

 it does not make much difference. When the dish is cold it is 

 weighed again, and so the loss of water is obtained. 



This method, which appears to be quite crude, really gives 

 surprisingly accurate results, and the author has found that 

 the mean difference between this method and the ordinary 

 method with pumice stone is on an average only + 0*17 per 

 cent. 



II. DETERMINATION OF THE FAT. 



(a) Scientific Methods. 

 1. The Extraction Method. 



If the fat of the butter is to be determined by the extraction 

 method, the residue left after the determination of the water is 

 used. With the help of a platinum spatula, the pumice 

 stone and the dried butter are transferred to one of the fat-free 

 cartridges made by Schleicher and Schull, and this put into a 

 Soxhlet extraction apparatus. Afterwards the dish is washed 

 out with small quantities of ether, which are poured on to the 

 cartridge. When all the fat has been washed from the basin, 

 a fairly thick layer of previously extracted cotton wool is placed 

 over the cartridge, which also rests upon a layer of similar 

 cotton wool 2-3 cm. thick. These precautions are necessary, 

 for otherwise some of the fine particles of pumice stone would 

 be carried over with the ether. The extraction with pure 

 ether must proceed for at least 12 hours, after which the ether 

 is evaporated off and the fat dried and weighed. This is done 

 in exactly the same manner as described in the extraction of 

 fat in milk (p. 49). 



