36 PROVISIONAL METHODS FOE ANALYSIS OF FOODS. 



3. DETERMINATION OF FAT. 



(a) OFFICIAL METHOD.* 



Dry about 5 grains of the sample on ignited asbestos in a Hofmeister schalchen or 

 in a perforated metal cylinder (described by Babcock) and extract with ether in a 

 continuous extraction apparatus. 



(b) BABCOCK'S METHOD. b 



This method is commonly used where a large number of samples is to be examined. 

 Owing to the general use of this method and its wide publication it is not deemed 

 advisable to introduce its description here. 



(c) GERBER'S METHOD. 



Where only occasional samples are to be examined Gerber's acid butyrometer is 

 found to give results comparable with those of the Babcock apparatus and is much 

 more convenient. Directions accompany the apparatus. 



4. DETERMINATION OF SOLIDS .NOT FAT. 



Deduct the percentage of fat from the percentage of total solids. 

 5. DETECTION OF GELATIN. c 



"An acid solution of mercuric nitrate is prepared by dissolving mercury in 

 twice its weight of nitric acid of 1.42 specific gravity, and diluting this solution 

 to 25 times its bulk by the addition of water. Ten cubic centimeters of the 

 milk or cream to be examined are mixed with an equal volume of the acid mercuric 

 nitrate solution, the mixture is shaken, and then 20 cc of water are added. The liquid 

 is again shaken, allowed to stand five minutes, and filtered. In the presence of much 

 gelatin the filtrate will be opalescent and can not be obtained quite clear. To a por- 

 tion of the filtrate contained in a test tube an equal volume of a saturated aqueous 

 solution of picric acid is added. A yellow precipitate will be produced in presence 

 of any considerable amount of gelatin, while smaller amounts will be indicated by 

 the cloudiness produced by the picric acid solution. In the absence of gelatin the 

 filtrate obtained will be perfectly clear, and will be unaffected by adding picric acid." 



6. DETECTION OF FORMALDEHYDE.* 1 



To the milk to be tested add strong commercial sulphuric acid without mixing, 

 and at the junction of the two liquids a violet or blue color will appear if the milk 

 contains one or more parts per 10,000 of formaldehyde. This color is supposed to be 

 given only when there is a trace of ferric chlorid or other oxidizing agent present. 



Other methods of detecting formaldehyde are described on pages 79 and 107. 



7. DETECTION OF BORAX AND BORIC ACID. 

 Use methods described on page 110. 



8. DETECTION OF FOREIGN COLORS. 

 (a) LEACH'S METHOD. e 



Warm about 150 cc of milk in a casserole over the flame and add about 5 cc of. 

 acetic acid, after which slowly continue the heating nearly to the boiling point while 



U. S. Dept. of Agr., Div. of Chem., Bui. 46 revised, p. 54. 



> Wis. Kxp. Sta. Bui. No. 24, and U. S. Dept. of Agr., Div. of Chem.. Bui. No.. 28, p. 34-42. 



Allen, Com. Org. Anal., 2d ed., Vol. IV, pp. 181-182. 



d See Appendix, ]>. 151. 



Jour. Am. Chem. Soc., 1900, 22, 207, 



