FOOD PRESERVATIVES. 



(d) HEH NEK'S METHOD.* 



185 



To the milk to be tested add strong commercial sulphuric acid without mix- 

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

 the milk contains one or more parts of formaldehyde per 10,000. This color is 

 supposed to be given only when there is a trace of ferric chlorid or other oxi- 

 dizing agent present. As pointed out by Hehner, milk may be treated directly 

 by this method without any other operation, and some other articles of food 

 rich in proteids for example, egg albumen give the reaction in the presence of 

 water without the addition of milk. The distillate described above may be 

 mixed with milk and this test applied. 



(e) LEACH'S METHOD. 



Add about 5 cc of the distillate obtained under (a) to an equal volume of 

 pure in ilk in a porcelain casserole and about 10 cc of concentrated hydrochloric 

 acid, containing 1 cc of 10 per cent ferric chlorid solution, to each 500 cc of 

 acid. Heat to 80 or 90 C. directly over the gas flame, giving the casserole a 

 rotary motion to break up the curd. A violet coloration indicates formalde- 

 hyde. 



(f) RIMINI'S METHOD. & 



Treat 15 cc of milk or other liquid food under examination or of the distillate 

 prepared as directed under (a) w r ith 1 cc of a dilute solution of phenylhydrazin 

 Imlrochlorid, then with a few drops of dilute ferric-chlorid solution, and, finally, 

 with concentrated hydrochloric acid. The presence of formaldehyde is indi- 

 cated by the formation of a red color, which changes after some time to orange 

 yellow. 



This method is suitable for the examination of milk without previous treat- 

 ment, but more delicate tests may be obtained from the distillate from milk or 

 from milk serum. The reaction is not interfered with by acetic aldehyde or 

 benzaldehyde. 



(g) PHLOROGLUCOL METHOD. c 



Prepare the reagent by dissolving 1 gram phloroglucol and 20 grams of sodium 

 hydroxid in sufficient water to make 100 cc. To 10 cc of milk or other liquid 

 food under examination in a test tube add, by means of a pipette, 2 cc of this 

 reagent, placing the end of the pipette on the bottom of the tube in such a 

 manner that the reagent will form a separate layer. 



A bright red coloration (not purple) is formed at the zone of contact if 

 I formaldehyde be present. This solution gives a yellow color in the presence 

 of some other aldehydes, and if it is used for the detection of aldehyde formed 

 by the oxidation of methyl alcohol after the destruction of ethyl aldehyde 

 with hydrogen peroxid an orange-yellow color will slowly appear when an 

 ; insufficient amount of hydrogen peroxid has been employed. On the other hand, 

 j if the excess of hydrogen peroxid is not fully destroyed before the use of this 

 [reagent a purple color will slowly form. The clear, red color given by the use 

 this reagent forms quickly, and in the presence of but a small amount of 

 formaldehyde soon fades. 



Analyst, 1895, 20: 155. 



"Ann. di Farmacol., 1898, 97: Abs. Chem. Centrbl., 1898, 69 (1) : 1152; Abs. J. Soo. 

 lem. Ind.. 1898, 17: 697. 



c Jorissen, Service de Surveillance des Aliments en Belgique, through Bui. soc. chim. 

 Big., 1897-98, 11: 12, 211 ; Abs. Analyst, 1897, 22: 282. 



