(d) HEHNER'S METHODS 



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 of formaldehyde per 10,000. This color is supposed to be given only when there is 

 a trace of ferric chlorid or other oxidizing 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, e. g., 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 milk 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 directly over the 

 gas flame, holding the casserole by the handle and giving it a rotary motion to break up the 

 curd. A violet coloration indicates formaldehyde. 



(f) RIMINI'S METHOD, c 



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

 directed under (a) with 1 cc of dilute solution of phenylhydrazin hydrochlorid; then with a 

 few drops of dilute ferric-chlorid solution; and finally, with concentrated hydrochloric acid. 

 The presence of formaldehyde is indicated 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 treatment, but more 

 sensitive results may be obtained from the distillate from milk or from milk serum. The 

 reaction is not interfered with by acetic aldehyde or benzaldehyde. 



(g) PHLOROGI.UCIN METHOD.^ 







Prepare the reagent by dissolving 1 gram of phloroglucin 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 formaldehyde be 

 present. This solution gives a yellow color in the presence of some other aldehydes, and if 

 it be 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, if the excess of hydrogen peroxid be not fully destroyed before the use of 

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

 reagent forms quickly, and in the presence of but a small amount of formaldehyde soon fades. 



(h) RESORCIN METHOD. 



This method has been suggested for the detection of formaldehyde formed by the 

 oxidation of methyl alcohol in flavoring extracts. Add to the liquid, prepared as directed 

 under flavoring extracts in Bulletin 65, 1 drop of a solution containing 1 part of resorcin 

 in 200 parts of water, and pour the mixture cautiously into a test tube containing 3 cc 

 of concentrated sulphuric acid, holding the tube in an inclined position in such a manner 

 that the two liquids shall not mix. Allow it to stand three minutes, then sway the tube 

 slowly from side to side in such a manner as to produce a gentle rotary motion of the two 



a Analyst, 1895, SO: 155. 



b Leach, Twenty-ninth Ann. Kept. Mass. Board of Health, 1897, p. 558. 



cAnn. di Farmacol., 1898, 97; Abs. Chem. Centrbl., 1898, 69, pt. 1: 1152; Abs. J. Soc. Chem. Ind., 1898, 

 17: 697. 



d Jorissen, Service de Surveillance des Aliments en Belgique, through Bui. soc. chim. Belg., 1897-98, 

 11: 12, 211; Abs. Analyst, 1897, 2S: 282. 



