167 



REPORT ON THE SEPARATION OF NITROGENOUS BODIES: MILK 

 AND CHEESE PROTEIDS. 

 By L. L. VAN SLYKE, Referee. 

 The referee selected the following subjects for investigation: 



(1) The acetic-acid-precipitation method for determining casein in milk, especially 

 with reference t<> the following points: 



(a) The use of less acid. 



(6) The influence of acid on the redissolving of casein. 



(r) The effect of temperature on the solution of casein by acetic acid. 



(d) The effect of various preservatives on the accuracy of the acetic-acid method. 



(2) The selection ,,f an official method by the association for the determination of 

 milk albumin. 



(3) A simple. rapid, ami accurate volumetric method for determining milk casein . 



F,,r the cooperative u<,rk of 1907-8 the referee selected the Matthaiopoulos volu- 

 metric method for the determination of casein. Results from only one of the cooper- 

 at.>r- WM received. The method is as follows: 



SOLUTIONS REQUIRED. 



I \:i .<:'M \miately i \venty-tifth-normal solution of sulphuric acid. 

 \ tenth-norm*] solution of sodium hydroxid. 

 \ 1 per cent alcoholic solution of phenolphthalein. 



Ml.THOD OF PROCEDURE. 



Into each of two 200 re beakers measure 20 cc of milk and 80 cc of water. Call one 

 A ami the niher />' Into .1 lei the i went \ -fifth-normal sulphuric acid run drop by 

 drop with c<>ri-iaiit -^tirrin_' of the diluted milk until the casein precipitates in large 

 flak-". After three to five minutes filter through a dry filter (S and S 589, 9cm, recom- 

 mended an. I collect the filtrate in a graduated, dry, 100 cc flask. If the first portions 

 of the lilt rai.- an- turbid, |*>ur back on filter. If the filtrate continues turbid, not 

 enough acjl has been used to precipitate the casein completely; in which case take 

 h sample and add 0.2 or 0.3 cc more acid. The amount of acid required varies 

 \\iih different milks, ranirinu' in the sample studied from about 23 to 27.5 cc. Any 

 M id must be avoided. Collect 1 00 cc of clear filtrate and transfer it to a beaker, 

 rinsinir ihe flask carefully, add I cc of the phenolphthalein solution and titrate to a 

 pal- pink color with tenth-normal sodium hydroxid. Note the number of cubic cen- 

 timeter- of alkali u-ed 



Treat theconteiiK <>f beaker li with twenty-fifth-normal sulphuric acid, usingexactly 

 the -line amount as in the case of .1. Add 1 cc of phenolphthalein solution and 

 titrate to a pale pink \\ith tenth-normal sodium hydroxid. Note the amount of alkali 



ll-ed 



The values obtained in .1 and B are then used in making the following calculations: 



in which /; H the amount of alkali used in titrating the mixture of water, milk, and 

 tweiity-fifth-nnrmal sulphuric acid; A is the amount of alkali used in titrating the fil- 

 trate;'// is the amount of twenty-fifth-normal sulphuric acid used in precipitating 

 in; <> II:'. I", i- a constant factor based on the equivalent weight of casein as shown 

 by Itottlte witb buee. The results are then calculated from 20 to 100 cc. 



Each cooperator \\a- requested to apply this method to samples of fresh milk of his 

 own selection and compare the results with those obtained by the official method. 



