102 



MILK AND DAIRY PRODUCTS PART 



0'5 mg. per 100 c.c., the blue colour appears after a few minutes ; 

 where the amount is less, say about 01 mg. in 100 c.c., several 

 hours may be needed. 



This test gives good results, but the method is too compli- 

 cated to make its use general in practice. 



(b) Fritzmann s 1 Nitrate Test. 



Fritzmann does not use diphenylamine, but shows the 

 presence of nitrates in milk by formalin and sulphuric acid. 



One drop of a 10 per cent, solution of formaldehyde is added 

 to 10 c.c. of milk and about 10 c.c. of chemically pure sulphuric 



FIG. 49. Apparatus for making the Nitrate Test. 



acid (sp. gr. 1*815), and the presence of nitrates in the milk is 

 indicated by a bluish-violet colour, only shown in the presence 

 of protein. 



Siegfeld 2 carries out the test by not mixing the two liquids, 

 but allowing the milk, to which a drop of formalin has been 

 added, to form a layer above the acid. Any violet coloration 

 then becomes apparent at the junction of the two liquids. Made 

 in this way, it is claimed by Siegfeld that the test is more 

 sensitive than with diphenylamine. 



Fritzmann and Reiss have arranged a testing apparatus, 

 which they call " Hydro," for the use of those dealing in milk. 



1 Zeitschrift fur o/entliche Chemie, 1897, No. 23. Ref. in Milch-Zeitung, 

 1898, p. 73. 



2 Molkerei-Zeitung, Hildesheim, 1902, No. 10. 



