Journal of Agriculture. [8 April, 1908. 



V. Storch^ with the object of utilizing this property of raw milk as a 

 basis for a differentiative test searched for a substance which if acted upon 

 by nascent oxygen would produce a colour change. He found potassium 

 iodide-starch to be a very suitable reagent for this purpose. He further 

 suggested and tried various organic compounds, such as guaiacol, hydro- 

 quinone, a-naphthol, paraphenylendiamine, pvrogallic acid, &c., and 

 finally declared paraphenylendiamine to be the most suitable reagent. 

 This compound in presence of the oxygen liberated from hydrogen per- 

 oxide causes a greyish blue colouration in milk. 



After Storch published his results the question was closely followed 

 up by numerous investigators who critically tested his methods. F. 

 Schaffer,* Utz,^ M. SiegfekF and others agreed with Storch, in view of 

 their own experiments, that paraphenylendiamine is the most suitable 

 reagent. du Roi and Kohler' however favoured a less costlv chemical 

 than paraphenylendiamine and experimented with potassium iodide and 

 starch which had previously (in 1899) been suggested by Storch but 

 condemned by him as not being sufficiently sensitive. Later on, Utz^ as 

 the result of further experience agreed with du Roi and Kohler's finding, 

 viz.. that the potassium iodide-starch process is of greater practical 

 importance than Storch 's for the reason that paraphenylendiamine will 

 not keep long, and that it is too costly. M. Siegfeld^ in 1903 subjected 

 all the known methods to critical examination and concluded that para- 

 phenylendiamine deserves first place among the methods, and subsequently 

 the paraphenylendiamine process was selected as the official method for 

 use m milk analysis in Italy (1904), France (1905), Switzerland (1905). 



Although the paraphenylendiamine process is now almost universally 

 adopted, it possesses several disadvantages. In addition to the two 

 objections raised by du Roi and Kohler and Utz, that the chemical is 

 too costly and does not keep well, there is another objection : the reaction 

 is far from being perfect in the case of raw Avhole milk. Bearing these 

 defects in mind we have endeavoured to find a more sensitive test than 

 that based on the use of paraphenylendiamine for identifying the oxygen 

 liberated from hydrogen peroxide by unboiled milk and have found a 

 suitable reagent in the organic base Benzidin (paradiamidodiphenyl NH^ 

 (C,;H^)2 (NH2). An alcoholic solution of benzidin acetate when brought 

 in contact at ordinary temperature with a solution containing nascent 

 oxygen immediately develops an intense blue colouration. The reaction 

 is carried out in a manner analogous to that \\\t\\ paraphenylendiamine : — 

 To TO cc. of the milk to be tested are added 2 cc. of an alcoholic solution 

 of Benzidin, then 2 to 3 drops of glacial acetic acid (just sufficient to 

 cause coagulation of the milk) shake the whole, and finally add 2 cc. of 

 a 3 per cent, solution of hydrogen peroxide. If the milk is unboiled or 

 or if it has not been heated to above 78 deg. C. an intense blue 

 colouration is immediately produced. Milk which has been heated to above 

 80 deg. C. do€'S not show any change by this treatment. It is advisable 

 to pour the hvdrogen peroxide solution slowly into the tilted test tube 



3V. Storch 4ode Beretninf; fra den Kgl. \ eterlnar. 0£t Landbo-hojskoles Labor- 

 atorium for landekonomiske Forsog. Kjobenhavn, 1898, A. Bang, 46S. 



■^F. SchafTer, Schweiz. Wochenschr, Chem. Pharm. 1900, 38, i6q and 209. 



5 Utz, Pharm. Centrh. 1901, 42, 149-150. 



6 Siegfeld, Milch Zeitung 1901,30, 723-725. 



7 Milch Zeitung, 1902, 31, 17-18. 



8 Milch Zeitung, 1902, 31, i4!;-i46. 

 ^Zeitschr. fur angewandte Chemie, 1003, 764. 



