442 R. H. A. PLIMMER AND W. M. BAYLfSS. 



it is quite unnecessary to use ice-cold water for washing the precipitate, 

 the whole of which may be collected on the filter. The precipitate is 

 then dissolved by the alkali on the filter and the solution allowed to 

 run into the original flask, into which the remainder, including, the 

 filter paper, is washed with water. 



With regard to the accuracy of the method, as modified by us, we 

 append the values which we have obtained with a standard solution of 

 acid potassium phosphate (10 c.c. = 20 mgm. P 2 5 ). 



(1) 10 c.o. = 20-03. (4) 10 c.c. = 19-78. (7) 10 c.c. = 19-65. (10) 10 c.c. = 20-03. 



(2) 10 c.c. = 20-03. (5) 10 c.c. = 19-78. (8) 10 c.c. = 19-65. (11) 10 c.c. = 20-67. 



(3) 10 c.c. = 19-91. (6) 10c.c.= 19-91. (9) 10 c.c. = 19-65. (12) 10 c.c. = 20-67. 



Mean 10 c.c. = 19 '98 mm. P 2 5 . 



In some cases 10 c.c. nitric acid, in others 10 c.c. sulphuric acid were 

 present. In all cases 30 c.c. of the ammonium nitrate solution were 

 added, this being essential for the precipitation of the ammonium phos- 

 pho-molybdate. It is advisable to avoid a great excess of ammonium 

 molybdate since rnolybdic acid may then be precipitated. Under these 

 conditions the method is extremely accurate. 



THE SEPARATION OF PHOSPHORUS FROM CASEINOGEN. 



A. Separation by Trypsin. Of the various methods which have 

 been adopted for studying quantitatively the action of trypsin, we have 

 employed the one put forward first by Hedin (9) in 1904, which was 

 subsequently utilised by Cathcart (10) and then again by Hedin (9) 

 himself. The method consisted in precipitating the digest with tannic 

 acid, whereby any unchanged albumin and albumoses, but not peptones 

 except imperfectly, are precipitated, and then estimating the phosphoric 

 acid in a measured volume of the filtrate by Neumann's method, 

 modified as above described. This phosphoric acid may be conveniently 

 referred to as the "soluble P 2 O 5 ." The materials employed were Merck's 

 caseinogen prepared by Hammarsten's method, and "Pancreatin absolut 

 Rhenania" generally in such amount that the digest contained 0'2 0'3 

 per cent, of dry enzyme. Toluene was used as the antiseptic in these 

 experiments and in those with pepsin, etc. 



At various periods of digestion at 38 C. varying from ten minutes 

 to several days 50 c.c. samples were removed with a pipette and dropped 

 into an equal volume of tannic acid solution (Cathcart's recipe diluted 

 with an equal volume of water). After allowing to stand for about 



