40 FOODS AND FOOD ADULTERANTS. 



uncertain results of some skilled microscopists, however, would indicate that the 

 difficulty is inherent in the method. It certainly is not simple, and is not calculated 

 to supersede the chemical methods now in use. 



Caldwell, 1 after references to the notices of the use of the microscope 

 in the examination of butter published up to that time (1882), says, 

 p. 519 : 



It is plain, therefore, that little dependence can he placed on any microscopic lest 

 of the genuineness of hnttor, at least so far as the ohsorvation of the crystalline forms 

 of foreign fats is concerned, for neither docs the ahsence of such forms prove that the 

 hutter does not contain oleomargarine, nor does their presence prove the adulteration. 



'Jn the other hand, Mylius 2 has shown that the polarization micro- 

 scope may be used for the detection of minute quantities of foreign fats 

 in butter. Pure butter gives with crossed Nicols a dark field, whereas 

 crystals of foreign fat will appear bright. Skalweit 8 recommends this 

 method highly, and affirms that even the kind of foreign fat present may 

 be determined. 



In spite of the generally unfavorable, opinions I feel sure that the 

 chemist who neglects to make a simple microscopic examination of a 

 suspected butter with polarized light and a selenite plate loses a valua- 

 ble qualitative indication of the character of the samples with which he 

 has to work. The melting of the sample of butter and its slow cooling 

 to secure good bi-refracting crystals I consider a much less valuable 

 indication than the simple observations above described. 



SPECIFIC GRAVITY. 



The determination of the specific gravity of a butter fat gives a most 

 valuable indication of its purity. The density of pure butter glycerides 

 is distinctly greater than that of the common adulterants, with the ex- 

 ception of cotton-seed oil. While this difference is not great, it is 

 nevertheless large enough to be easily detected by careful manipulation. 



Manipulation. The relative weight of the filtered and dried fat is to 

 be determined in a picnomcter. This flask should be carefully cali- 

 brated by weighing the pure distilled water it will contain at the tem- 

 perature at which the subsequent determinations are to be made. The 

 Mask should be provided with a delicate thermometer, but this is not 

 essential, since the temperature can be determined by an external ther- 

 mometer. 



The temperature at which the determinations should be made is evi- 

 dently that at which all the common butter adulterants will be in. a 

 perfectly fluid state. Generally the temperature of 100 F. has been 

 employed. Since, however, "neutral lard" may have a melting point 

 as high as 40 0. or even a little above that I have uniformly taken the 

 specific gravity at that degree. In case the fat should have a melting 

 point a little above this the temperature can be raised until the fat is 



1 Second Ann. Kept. N. Y. S. Bd. of Health. 



2 Correspondenshlatt des Vereins Anal. Chem., 1878, No. 3. 

 ^ IMd., 1879, Nos. 5 and 13. 



