5. FORMALDEHYDE. 



(a) PREPARATION OF SAMPLE. 



If the material be solid or semisolid, macerate from 200 to 300 grams in a mortar with 

 about 100 cc of water until a sufficient degree of fluidity is obtained. Transfer to a short- 

 necked distilling flask of copper or glass of from 500 to 800 cc capacity and make distinctly 

 acid with phosphoric acid. Connect flask with glass condenser and distill from 40 to 50 cc. 

 In the case of liquids acidify with phosphoric acid and distill. 



(b) PHENYLHYDRAZIN HYDROCHLORID METHOD.a 



Mix 5 cc of the distillate as prepared under (a), or of an alcoholic solution or extract from 

 the substance under examination, with 0.03 gram of phenylhydrazin hydrochlorid, and 4 or 5 

 drops of a 1 per cent solution of ferric chlorid. Add slowly and with agitation in a bath of 

 cold water to prevent the heating of the liquid, from 1 to 2 cc of concentrated sulphuric acid. 

 A precipitate is formed which can be dissolved by the addition of either concentrated sul- 

 phuric acid, keeping the mixture cool, or alcohol. With meats and fats the formaldehyde 

 should first be extracted with alcohol and the filtrate tested. In the case of fat it is necessary 

 to heat the mixture above the melting point of the fat to insure thorough extraction. Milk 

 is shaken with an equal volume of strong alcohol and the filtrate employed. Other liquids 

 are shaken with an equal volume of strong alcohol and filtered in case of the formation of 

 any insoluble matter. 



In the hands of different analysts this method is found to give reliable reactions for formal- 

 dehyde in solutions of formaldehyde varying from 1 part in 50,000 to 1 part in 1.50,000. 

 Acetic aldehyde and benzaldehyde give no reaction when treated by this method and do not 

 interfere with the reaction given by formaldehyde. 



(c) PHENYLHYDRAZIN HYDROCHLORID AND FERRICYANID METHOD. & 



This method may be applied directly tc liquid foods or to an aqueous or alcoholic extract 

 of solid foods. To from 3 to 5 cc of liquid food or extract of the same add a lump of phenyl- 

 hydrazin hydrochlorid about the size of a pea, from 2 to 4 drops (not more) of a 5 to 10 per 

 cent solution of potassium ferricyanid, and from 8 to 12 drops of an approximately 12 per 

 cent solution of sodium hydroxid. The method is not applicable to preparations containing 

 blood-coloring matter. In such cases nitroprussid may be used in place of the ferricyanid. 

 Alcoholic extracts from foods must be diluted with water to prevent the precipitation of 

 potassium ferricyanid. 



Milk may be examined directly. Meat may be finely comminuted, extracted with 2 

 volumes of hot water, and the liquid pressed out and employed for the test. Fats are 

 warmed above the melting point with 10 cc of alcohol (from 80 to 95 per cent) thoroughly 

 shaken, cooled, and filtered with a moistened paper, and the filtrate employed. 



When formaldehyde is present to the extent of more than 1 part in 70,000 to 80,000 in the 

 solution tested, a distinct green or bluish green reaction is obtained. In more dilute solu- 

 tions the green tint becomes less marked and a yellow tinge tending toward greenish brown 

 is formed. 



With this method acetic aldehyde and benzaldehyde give a color varying from red to 

 brown, according to the strength of the solution. A reaction may, therefore, be obtained 

 with these aldehydes similar to that obtained with formaldehyde in solutions more dilute 

 than 1 part in 70,000. The presence of acetic aldehyde or benzaldehyde together with for- 

 maldehyde gives a yellowish or yellowish green tinge. The reaction for formaldehyde may, 

 therefore, be masked by the presence of other aldehydes, but is characteristic when a clear 

 green color is obtained. 



a Arnold and Mentzel, Zts. Nahr. Genussm., 1902, 5: 353. 



& Arnold and Mentzel, Chem. Ztg., 1902, 26:24.6; Abs. J. Chem. Soc., 1902, (2), 82:367; Abs. Chem. 

 Centrbl., 1902, 73, pt. 1: 1077. 



