Butyro-refractometer

Index of refraction. From 50 grams of the sample the fat is separated either by simple fusion at 1000 or by boiling with water and separating the layer of fat. The latter is examined in the Zeiss butyro-refractometer at 40° [see Butter, Chapter II). If the index exceeds 51-5°, the presence of horseflesh is probable. 

Butyro-refractometer Reading. -The Zeiss butyro-rcfractometer, here described (see Fig. f>), is l modification of the ordinary Abb[Pg.36]

Butter giving a butyro-refractometer reading higher than 48 at 350 may, without further test, be taken as adulterated. Also recently made butter which, in polarised light, shows a crystalline structure, is to be regarded as adulterated if the butter is not known to be of recent preparation, the crystalline structure renders it suspicious. Further, butter having at ioo° a lower specific gravity than 0-865, with reference to water at 150, is to be taken as adulterated. 

Refractive Index.—As with essential oils at 15°.2 Use may be made of the butyro-refractometer (see p. 36), the results being expressed as degrees on this instrument at 15 °. 

The refractive index at 15° is r 468-1 478 and the reading on the Zeiss butyro-refractometer at 15°, 66-73, most French and American oils having values between 70 and 73 and Greek oil the value 66. Mineral oils lower the refractive index, whilst tar oils raise it. 

Refraction. This serves especially for the identification of oil of turpentine and for the detection of any added mineral oil the determination is made with the Zeiss butyro refractometer at 150 C. (see p. 36). 

Refractive Index (butyro) Determine as directed under Refractive Index, Appendix IIB, using a melted sample filtered through filter paper. Determine the refractive index at 48° with an Abbe or butyro refractometer. 

Where a great number of samples have to be tested expeditiously, the Abbe refractometer or the Zeiss butyro-refractometer may be recommended on account of the ease with which they are manipulated. The most usual temperature of observations is 60 C. 

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