3 2 4 



PHYSIOLOGICAL CHEMISTRY 



i 



This test may form the basis of a quantitative method by diluting 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 aqueous solution of 

 para-phenylenediamine hydrochloride to 10-15 c.c. of milk. If hydrogen peroxide 

 is present a blue color will be produced 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 Borates. To the ash, obtained accord- 

 ing to the directions given in Experiment 4, page 327, add 2 

 drops of dilute hydrochloric acid and i c.c. of water. Place a 

 strip of turmeric 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 supposed to show boric acid 

 F5| when present in the proportion i : 8000. 



Quantitative Analysis of Milk 



1. Specific Gravity. This may be determined con- 

 veniently by means of a Soxhlet, Veith, or Quevenne 

 lactometer. A lactometer reading of 32 denotes a 

 specific gravity of 1.032. The determination should 

 be made at about 6oF. and the lactometer reading 

 corrected by adding or subtracting 0.1 for every degree 

 F. above or below that temperature. 



2. Fat. (a) Babcock's Centrifugal Method} Prin- 

 ciple. The principle of this method is the destruction 

 of organic matter other than fat by sulphuric acid and 

 the centrifugation of the acid solution in the special 

 tube shown in Fig. 106 and the subsequent reading of 

 the percentage of fat by means of the tube's gradu- 

 ated neck. The method is one of the most satisfac- 

 tory in common use and is accurate to within 0.5 per 

 cent. 



ICC. 



FIG. 1 06. BAB- 

 COCK TUBE. 



Procedure. By means of a special narrow pipette introduce milk into the 

 tube up to the 5 c.c. mark. Now add sufficient sulphuric acid (sp. gr. 1.83- 

 1.834) to fiH the body of the tube and rotate the tube to secure a homogeneous 

 acid-milk solution. Fill the neck of the tube with an acid-alcohol mixture. 2 

 Centrifuge the tube and contents for one to two minutes and read off the per- 

 centage of fat by means of the graduated neck of the tube. If the top of the fat 



1 A modification of this method for use with sweetened dairy products, e.g., ice cream, 

 and entailing the use of a different type of centrifuge tube has been proposed by Halverson 

 (Jour. 2nd. and Eng. Chem., 5, 403, 1913). 



2 This mixture consists of equal volumes of amyl alcohol and concentrated hydrochloric 

 acid. 



