PRODUCTS OF RIPENING. 



.239 



Nitrogen as Caseoses. To the filtrate from the last deter- 

 mination add 1 c.c. of 50 per cent, sulphuric acid, saturate with 

 zinc sulphate, and warm to 70 C. Cool the solution, filter, wash 

 with a saturated solution of zinc sulphate, and estimate the 

 nitrogen in the precipitate. 



Nitrogen as Amino-acids and Ammonia. To TOO c.c. of the 

 aqueous solution of the cheese add 1 gramme of sodium chloride, 

 and tannin solution till the precipitation is complete ; filter 

 and dilute the filtrate to 250 c.c., and Kjeldahl an aliquot portion. 

 This will give the nitrogen as amino -acids and ammonia ; the 

 ammonia is estimated in another aliquot portion by making 

 alkaline with a little magnesia, and distilling the ammonia into 

 standard acid. 



Nitrogen as Peptone. The difference between the water soluble 

 nitrogen and the sum of the other determinations will give the 

 nitrogen as peptone. 



Nitrogen as Mono-calcium Caseinats. The portion of the cheese 

 insoluble in water is treated with successive portions of ICO c.c. 

 of a 5 per cent, sodium chloride solution, in a manner similar 

 to the treatment with water, and the nitrogen as mono-calcium 

 caseinate is estimated by the Kjeldahl method in an aliquot 

 portion of the solution. 



Devarda's Method. Devarda recommends for the deter- 

 mination of water that about 10 grammes of finely-divided 

 cheese should be dried in vacuo over sulphuric acid for twenty- 

 four to thirty-six hours, and then for two to six hours at 100 C. 

 until the weight becomes constant. In this way the bulk of 

 water is removed at the ordinary temperature, and, whilst the 

 method is fairly quick, there is no material loss of organic matter, 

 such as occurs with long-continued drying at 100 C. Complete 

 drying in vacuo is too tedious and often impracticable. 



The following examples show the accuracy of this process : 



TABLE XLV. 



