150 PROVISIONAL METHODS FOE ANALYSIS OF FOODS. 



valuable when taken in conjunction with some other measurement (volatile acid, 

 iodin, absorption, etc.)- A fairly constant ratio may often be observed between the 

 specific gravity and other measurements for a particular oil. Addition of an adul- 

 terant may upset this relationship without, however, bringing the specific gravity 

 (or other measurement) outside the limits for the pure oil. Edgar B. Kenrick. 



Page 22, 2, (b), (2). Why not use Westphal balance to determine specific gravity 

 at temperature of boiling water? A. G. Woodman. 



Page 22, 3. I think it is time that a vigorous protest be made against the practice, 

 now becoming quite common, of reporting refractive indices by purely arbitrary 

 numbers. One would think that the confusion resulting from the use of Twaddell, 

 Baume", etc. , degrees of specific gravity should be sufficient warning. 



The omission of any statement as to the optical relation between the readings of 

 the Zeiss instrument and the refractive indices leaves the reader in doubt as to 

 whether the table given is of any use beyond the individual instrument for which it 

 was constructed. The writer of a recent text-book on physical measurements gives 

 at the end of the book a table for the conversion of the readings of the Pulfrich 

 refractometer into refractive indices. No warning is given to the reader that the 

 table will not apply to any Pulfrich refractometer. The table, in fact, is quite useless 

 for the instrument now in use in my laboratory. The index of refraction in the 

 Pulfrich instrument is the square root of the difference between the square of the 

 refractive index of the glass prism and the square of the* sine of the angle measured. 

 Since the refractive index of the prism in any particular instrument is not the same 

 as that of the one for which the table in the book is made, it is obvious that the said 

 table can not be used with my instrument. 



After an experience of twelve years with two forms of the Pulfrich refractometer, 

 I am able to say that this instrument leaves nothing to be desired in point of accuracy 

 and ease of operation. Edgar B. Kenrick. 



Page 25, 4. In weighing the fat for determination of iqdin absorption I use Wes- 

 son's small, flat-bottomed glass cylinders and a narrow-mouthed bottle. (See our 

 report for 1896, p. 23. ) Would it not be well to make the instruction a little more 

 elastic, so as to cover any form of glassware found efficient? A. L. Winton. 



Referring to the "wide-mouth bottle," I should prefer small glass stopper on 

 account of greater danger of loss of iodin from large one. A. G. Woodman. 



Page 26, 5, (a). It has always been customary in the laboratory at Munich, 

 Bavaria, under Professor Hilger, to keep the solutions of iodin and mercuric chlorid 

 separate. They were mixed in equal proportions forty-eight hours before use. 

 Emil ScMichting. 



Page 26, 5, (b) and (c). Instead of about 5 grams of the melted fat, I think it 

 better to use from 1 to 2 grams. Instead of a reflux condenser, I prefer a small 

 funnel placed in mouth of flask. This is perfectly satisfactory and more con- 

 venient. A. G. Woodman. 



Page 29, 11. The method of using 5 grams of fat is satisfactory for most analytical 

 work, but that I may be able to present a sample of the adulterant found as evidence 

 in court, in the case of adulterated linseed oils, it has been my practice to use 10 

 grams, following the method of Morawski and Demski, page 172 of Benedikt and 

 Lewkowitzch (Oils, Fats, and Waxes). By this method the removal of the alcohol 

 used in saponification is avoided, as is also to a great extent the solubility of the 

 alkaline soap solution in ether. 



Ten grams of fat are saponified in a flask with 5 grams of caustic potash dissolved 



