THE FUSING POINT. 25 



By using such a -weight, the sinking points of all butters 

 come within the Hmits of three degrees, and any numher of 

 observers witnessing an experiment would agree when to 

 read the thermometer. Beef, mutton, pork, and other fats are 

 also equally constant, providing they are taken from the same 

 part of the animal. 



Further, in mixtures of foreign fats with butter, the 

 sinking point varies in ratio to the percentage composition of 

 the mixture, so much so, that in many instances the result 

 arrived at by previous mathematical calculation practically 

 coincides with the sinking point obtained. 



Dripping or kitchen stuff, being often a mixture of dif- 

 ferent fats in unknown proportions, and having a sinking 

 point very near that of butter itself, is an adulterant the 

 presence of which the sinking point may give no indication ; 

 in this case recourse must be had to the estimation of fatty 

 acids, which process will be spoken of further on. The 

 reason why dripping has such a low sinking point is probably 

 because it is composed of that part of the fat which is most 

 easily fused in the process of cooking j in other words, it 

 contains comparatively little stearin. 



To take the sinking point of a butter, place 20 to 30 

 grammes of butter in a porcelain dish or glass beaker, and 

 melt in the water-bath ; when quite fluid, pour into a test- 

 tube of f -inch interior diameter, and about 6 inches long, 

 until filled to within about two inches of the top. Keep the 

 tube warm untU the whole of the water, salt, and casein has 

 sunk, and left a perfectly clear fat ; now soHdify by immers- 

 ing the tube in water of 15° temperature. When quite cold, 

 notice whether a dimple or hollow cone be formed upon the 

 top ; if so, it is a fact of sufficient importance to give rise to 

 suspicion. Pure butter shows only a slight depression, 

 whereas mixtures of a fat having a high fusing point, with 

 butter, cool with a hollow cone ; an admixture of 20 per cent. 



