347 
1910-11.] Small Degrees of Enzymatic Peptolysis. 
the contents filtered in the ordinary way. The precipitates were well 
washed with cold water and finally dried in an oven. It is necessary to 
remove by washing all trace of the pepton solution, as this itself gives a 
slight green colour with the reagent. This does not, however, present 
any difficulty. The dried precipitates were now dissolved in measured 
quantities of the solvent acid. 
The quantity of reagent employed was in each case determined by the 
approximate quantity of tyrosin, but the same volume of reagent will give 
suitable readings within a fairly wide range of tyrosin. Therefore, if an 
apparently large precipitate is obtained, a large quantity of reagent is 
employed in preference to diluting a possibly too dark liquid after the 
reaction. This latter method has been found to give inaccurate results. 
The acid was allowed to run on to the filter paper from a burette, the 
solution being received in a flask graduated for the final amount of reagent 
to be used. For 20 c.c. reagent, 9*8 c.c. of the solvent acid was used and 
was received in a 20 c.c. flask. To this was added 2 c.c. of formol. 
Finally, 10 c.c. concentrated sulphuric acid was added, the contents of the 
flask well mixed by stirring or shaking, and the flask immersed in a bath 
of boiling water. In these experiments the flasks have been allowed to 
remain in the bath for twenty minutes, after which they have been cooled 
in water. The period of boiling — twenty minutes — was simply fixed upon 
as giving ample time for the completion of the reaction, and also in order 
to minimise the possible experimental error due to slight variations in the 
time. Since some shrinkage always occurred, the contents of the flask, 
when cool, were made up to the graduation mark with sulphuric acid of the 
same concentration as the reagent. The colour was now estimated by 
means of the tintometer. 
The usual method of estimating colour is by matching it as nearly as 
possible. In a paper read before the Society of Chemical Industry, Dr 
Westergaard describes a method of estimating colour by neutralisation. 
This method has been adopted in preference to the former, in these 
experiments, partly because it appeared easier to decide when a colour was 
neutralised than when it was exactly matched, and also because the 
neutralisation of the green colour may be effected by a single red slide, 
while matching would at least demand two. The estimation becomes 
considerably simplified when only a single slide is required for each 
determination. It is now a comparatively simple matter to discover a red 
slide of such intensity that, on superposition, the green colour of the 
solution is entirely neutralised. 
As the method is based upon the formation of tyrosin by the hydrolysis 
