382 OTHER MILK PRODUCTS. 



Van Slyke's Method, for the Estimation of the Products 

 of Ripening. — 25 grammes of cheese are well mixed in a mortar 

 with an equal volume of quartz sand, and transferred to a flask ; 

 100 c.c. of water at about 50° C. are added, and the mixture 

 kept at 50° to 55° for half an hour with frequent shaking. The 

 liquid is filtered through cotton wool into a 500 c.c. flask, and 

 the residue is treated as before with four further successive 

 quantities of 100 c.c. of water ; after cooling the volume is made 

 up to the mark. 



Water-soluble Nitrogen. — This is estimated by the Kjeldahl 

 method in 50 c.c. of the solution. 



Nitrogen as Paranuclein. — Five c.c. of a 1 per cent, solution of 

 hydrochloric acid are added to 100 c.c. of solution, and digested 

 at 50° to 55° G. till the precipitate has completely separated. 

 The precipitate is filtered, and washed, and the nitrogen esti- 

 mated by the Kjeldahl method. 



Nitrogen as Goagulable Protein. — Neutralise the preceding fil- 

 trate, heat to boiling, and estimate the nitrogen in the precipitate, 

 if any ; ooagulable proteins rarely occur in cheese. 



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 100 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 difEerenoe between the water soluble 

 nitrogen and the sum of the other determinations will give the 

 nitrogen as peptone. 



Nitrogen as Mono-calcium Oaseinate. — The portion of the cheese 

 insoluble in water is treated with successive portions of 100 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 

 •oaseinate 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- 

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

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



