74 CHEMICAL EXAMINATION 



of 30 per cent caustic soda, followed by 10 c.cms. of a 10 per 

 cent solution of potassium sulphide. The flame is placed under 

 the flask, and the distillation continued until about 200 c.cms. 

 have passed over. Before taking away the flame, the tap of 

 the funnel should be opened to prevent creating a partial vac- 

 uum and so drawing back the distillate into -the flask. The 

 end of the condenser is washed with water, and the washings 



N 

 mixed with the distillate which is finally titrated with caustic 



alkali using sensitive methyl orange or, preferably, methyl red 



N 

 as the indicator. Each c.cm. of acid neutralised = 0.0014 



grm. nitrogen or 0.028 per cent of nitrogen when 5 grms. of milk 

 are used. The percentage of nitrogen multiplied by 6.38 gives 

 the percentage of total proteids. 



In all determinations of nitrogen by the above method, it is 

 essential that a blank determination should be made on all the 

 reagents and this amount deducted from all subsequent results. 



Caseinogen. Dilute 10 gms. of the sample with about 90 

 c.cms. of water at 40 to 42 C. and add at once 1.5 c.cm. of a 

 10 per cent acetic acid solution. Stir with a glass rod and allow 

 to stand for about five minutes. Decant on to a wet filter, 

 wash several times with cold water by decantation and then 

 transfer the precipitate completely to the filter. Wash once 

 or twice with cold water. If the filtrate is not bright it should 

 be refiltered until that condition is attained. The nitrogen in 

 the precipitate is then estimated as above by the Kjeldahl 

 method. The percentage of nitrogen multiplied by 6.38 gives 

 the percentage of caseinogen. This method is only applicable 

 to fresh milk. 



Albumin. The filtrate from the precipitation of caseinogen 

 is first exactly neutralised with caustic alkali and then acidified 

 by the addition of 0.3 c.cm. of a 10 per cent solution of acetic 

 acid. After heating to boiling over a flame, the precipitate is 

 digested on the water bath for fifteen minutes. The liquid is 

 filtered through paper, the precipitate washed and finally used 



