MICROSCOPIC EXAMINATION OF BUTTER. 17 



tissue, the contents of which depolarise light in an irregular 

 manner. 



Pure butter, freshly made, has no effect upon polarised 

 light, except when it has been heated and allowed to cool 

 again; when cooled very rapidly no perfect crystals are 

 formed. 



One part of ox fat and two parts of butter fat melted and 

 poured into cold water, exhibited no traces of crystals, but 

 contained much water, which might have been expelled by 

 pressure. 



If, therefore, upon crushing a small portion of the sample 

 into a thin layer, and viewing it by polarized light, it shows 

 stellate masses of crystals, it is a proof that some part of the 

 fat has been melted down ; and if no definite crystalline 

 forms can be made out, but some portion or the whole of the 

 mass possess any power over the polarised ray, it is probable 

 that an animal fat has been added whilst in a state of fusion, 

 and that the mixture was rapidly cooled. 



It must not be forgotten that it is quite possible that in 

 the summer time the outside portion of a pure butter may 

 have fused and become crystalline. If some of a fat contain- 

 ing crystals be placed upon a slide, and a drop of castor or 

 olive oil be applied, and pressed out with a thin glass cover, 

 the depolarisation of light is much enhanced. A revolving 

 black cross, not unlike that on some starch grains, is seen in 

 great perfection. These crosses are most clearly defined in 

 the crystals obtained from butter, and these thus mounted 

 form a brilliant polariscope object for a one-third lens. The 

 oil, however, exerts a solving action upon the crystals, and 

 they soon disappear. 



Thus far and no farther, as it seems to us, can the micro- 

 scope assist us in this matter, but even such indications are 

 valuable, especially when subsequent analysis proves the 

 sample to be an adulterated article, the microscopic evidence 



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