212 REPORT OF THE CHEMIST OF THE 
was avoided, as well as by agreement of the equilibria obtained by 
different methods of treatment. (See Fig. 8 and Table XVIII for 
examples. ) 
GENERAL OUTLINE OF METHOD OF MEASURING ACIDITY. 
The method of finding the amount of acid taken up by a given 
weight of casein was, briefly stated, as follows: The casein was 
agitated in a Jena Erlenmeyer flask with a measured volume of 
acid of known strength for a given period of time, after which 
it was filtered and the amount of acid taken up by the casein 
was ascertained by means of the decrease in the conductivity of 
the solution. In a part of the work, titration results with N-10o 
NaOH were obtained for comparison with the conductivity results. 
The details of the method will be considered in the following 
order: (1) Preparation of flasks, (2) preparation of standard 
solutions, (3) measuring solutions for use, (4) preparation of con- 
ductivity water, (5) methods of agitation, (6) introducing casein 
into the acid solution, (7) filtration, (8) method of measuring con- 
ductivity, (9) data illustrating accurracy of method, (10) calcu-~ 
lating conductivity results in terms of concentration of acid. 
PREPARATION OF FLASKS. 
Jena Erlenmeyer flasks holding 200 cc. were used in holding 
the acid and casein for reaction. It is important to use glassware 
which on contact with solutions will not affect the conductivity. 
Jena glassware was found to meet this requirement and it was 
employed in all operations where solutions were in contact with 
glassware for any considerable period of time. Before being used, 
the flasks were carefully cleaned, rinsed with distilled water, then 
with conductivity water and finally dried in a steam oven. 
Rubber stoppers, thinly coated with paraffin, were used in these 
flasks ; the stoppers were thoroughly rinsed with conductivity water 
and then dried on clean filter paper before being used. A test of the 
effect of paraffin showed it to be practically without influence upon 
the conductivity of water. 
* Beitr. Chem. Physiol. u. Pathol., 3:206. 1903. 
* Jour. Physiol., 23:273. 1905. 
