184 METHODS OF ANALYSIS. 



(b) PHENYLHYDBAZIN HYDROCHLOBID METHOD.** 



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 phenylhy- 

 drazin 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 sulphuric 

 acid (keeping the mixture cool) or with alcohol. With meats and fats the for- 

 maldehyde 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 reac- 

 tions for formaldehyde in solutions of formaldehyde varying from 1 part in 

 50,000 to 1 part in 150,000. Acetic aldehyde and benzaldehyde give no reaction 

 when treated by this method and do not interfere with the reaction given by 

 formaldehyde. 



(c) PHENYLHYDBAZIN HYDBOCHLOBID AND FEBBICYANID METHOD. & 



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

 alcoholic extract of solid foods. To from 3 to 5 cc of liquid food or extract of*i 

 the same add a lump of phenylhydrazin 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 I 

 sodium hydroxid. The method is not applicable to preparations containing 

 blood-coloring matter. In such cases use nitroprussid in place of the ferri- 

 cyanid. Alcoholic extracts from foods must be diluted with water to prevent 

 the precipitation of potassium ferricyanid. 



Apply the method directly to milk without any preparation of sample. In thoj 

 case of meat finely comminute the sample, extract with two volumes of hot 

 water, and employ the liquid pressed out for the test. Warm fats above the 

 melting point with 10 cc of alcohol (80 to 95 per cent by volume), thoroughly 

 shake, cool, and filter through a moistened paper, using the filtrate for thej 

 examination. 



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

 to 80,000 in the solution tested, a distinct green or bluish green reaction is 

 obtained. In more dilute solutions the green tint becomes less marked and aj 

 yellow tinge tending toward greenish brown is formed. 



With this method acetic aldehyde and benzaldehyde give a color varying froml 

 red to brown, according to the strength of the solution. A reaction may there-l 

 fore be obtained with these aldehydes similar to that obtained with formalde-l 

 hyde in solutions more dilute than 1 part in 70,000. The presence of acetic! 

 aldehyde or benzaldehyde together with formaldehyde gives a yellowish orl 

 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. 



_ _ 



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



^Arnold and Mentzel, Chem. Ztp., 11)02. 26: 246; Abs. J. Chem. Soc., 1902, 82 (2)11 

 367; Abs. Chem. Centrbl., 1902, 78 (1) : 1070. 



