64 DETECTION OF PRESERVATIVES. 



V. FORMALIN. 



This substance, which has now come into general use 

 as a food preservative, according to some authorities, 

 may be properly used as a preservative for milk. The 

 commercial preparation "Formalin" consists of a 40 per 

 cent solution of formaldehyde in water. The detection 

 of it in milk is a simple matter.* By adding a solution 

 of silver nitrite to the milk a black precipitate is formed 

 when formaldehyde is present. In case of very small 

 amounts of formahn, the nitrite solution produces usual- 

 1)', on standing, only a brownish black stain or coloration, 

 due to the production of finely divided metallic silver. 

 The preservative action of formalin is especially marked. 

 It has been found that milk may be kept 100 hours at 25 

 degrees C. when formalin is added in the proportion of 

 one part of formaldeyde to 5,000 parts of milk. When 

 added in such small amounts, formalin changes neither 

 the odor nor the taste of milk. Notwithstanding this, its 

 use as a preservative of milk intended for food should be 

 prohibited since it has been shown that even with dilute 

 solutions it retards digestion and also alters the compo- 

 sition of the milk. Upon the albuminoids especially it 

 exerts an influence tending to increase the solubiHty of 



*For the detection of formaldehyde in milk a method has re- 

 cently been proposed making use of phloroglucin solution, o.i 

 gram of phloroglucin is dissolved in 100 c. c. of water. 1-2 c. c. 

 of this solution is treated with a few drops of potassium or sodi- 

 um hydroxide and added to eight or ten c. c. of the milk to be 

 tested. In the presence of formaldehyde a red coloration is pro- 

 duced. According to Jorrissen one part in 20,000 may be easily 

 detected in this way. This reaction with phloroglucin takes 

 place only with dilute formaldehyde solutions. Vanino found 

 that ten to thirty per cent solutions gave no reaction, or at best 

 only a slight coloration. A three per cent solution produces a 

 deep red color. The strongest color is produced by 0.5 per cent. 

 With solutions containing 0.00004 per cent formaldehyde the 

 color is distinctly visible but when more highly diluted it does 

 not respond distinctly to the phloroglucin test. See Zeitsch. fur 

 Anal. Chemie, 1900, page 64. — Translators. 



