226 PHYSIOLOGICAL CHEMISTRY. 



10 c.c. of concentrated hydrochloric acid containing about 0.002 

 gram of ferric chloride in a small porcelain evaporating dish or 

 casserole and gradually raise the temperature of the mixture, on 

 a water-bath, nearly to the boiling-point, with occasional stirring. 

 If formaldehyde is present a violet color is produced, while a brown 

 color develops in the absence of formaldehyde. In case of doubt 

 the mixture, after having been heated nearly to the boiling-point for 

 about one minute, should be diluted with 5075 c.c. of water, and 

 the color of the diluted fluid carefully noted, since the violet color 

 if present will quickly disappear. Formaldehyde may be detected 

 by this test when present in the proportion i : 250,000. 



(&) Salicylic and Salicylates. Remont's Method. 1 Acidify 20 

 c.c. of milk with sulphuric acid, shake well to break up the curd, 

 add 25 c.c. of ether, mix thoroughly and allow the mixture to 

 stand. By means of a pipette remove 5 c.c. of the ethereal extract, 

 evaporate it to dryness, boil the residue with 10 c.c. of 40 per cent 

 alcohol and cool the alcoholic solution. Make the volume 10 c.c., 

 filter through a dry paper if necessary to remove fat, and to 5 c.c. 

 of the filtrate, which represents 2 c.c. of milk, add 2 c.c. of a 2 per 

 cent solution of ferric chloride. The production of a purple or 

 violet color indicates the presence of salicylic acid. 



This test may form the basis of a quantitative method by dilut- 

 ing the final solution to 50 c.c. and comparing this with standard 

 solutions of salicylic acid. The colorimetric comparisons may be 

 made in a Duboscq colorimeter. 



(c) Hydrogen Peroxide. Add 2-3 drops of a 2 per cent aque- 

 ous solution of para-phenylenediamine hydrochloride to 10-15 c - c - 

 of milk. If hydrogen peroxide is present a blue color will be pro- 

 duced immediately upon shaking the mixture or after allowing it 

 to stand for a few minutes. It is claimed that hydrogen peroxide 

 may be detected by this test when present in the proportion 

 i : 40,000. 



(d) Boric Acid and B orates. To the ash, obtained according 

 to the directions given in Experiment 4, Chapter XXIII, add 2 drops 

 of dilute hydrochloric acid and i c.c. of water. Place a strip of tur- 

 meric paper in the dish and after allowing it to soak for about one 

 minute remove it and allow it to dry in the air. The presence of boric 

 *acid is indicated by the production of a deep red color which changes 

 to green or blue upon treatment with a dilute alkali. This test is sup- 

 posed to show boric acid when present in the proportion i : 8000. 



'Sherman's Organic Analysis, p. 232. 



