RICHARDS: DETERMINATION OF ACIDITY 243 
By the method outlined we may obtain first a sample of pure 
juice to determine concentration and second the total amount of 
acid contained in a given weight of tissue. Where total acidity 
alone is required the speaker has used a simple method which is 
not in any way original but which by repeated test has been shown 
to be satisfactory and to yield very consistent results. Briefly 
the process is this. A small sample of the tissue is ground in a 
mortar with a little water and carefully washed silica sand. This 
is then strained through glass wool: the pulp and wool are again 
ground and strained and if there is evidence that the tissue is not 
finely enough comminuted by this time the process is repeated. 
The various samples are then mixed together and filtered into a 
graduated flask, care being taken to wash the filter thoroughly. 
An aliquot portion of the known volume is titrated as usual. 
Before finally rejecting the pulp it should be tested to determine 
if it is acid-free. This process may be carried on with considerable 
speed and the whole determination may be completed within 
fifteen minutes of the time of taking the sample. Time may also 
be gained by the use of a centrifuge in place of the filtering. 
One thing, perhaps, is evident in the methods outlined, that 
is, the quickness with which the processes may be carried on, and 
it is Оп this point I wish to lay especial stress. We know that the 
organic acids with which we are dealing in plants are in many cases 
highly unstable and that if considerable time elapses between 
their extraction and estimation changes may occur that will 
influence the final result. Also the acids are easily affected by 
any substances that may be added to the solutions. Conse- 
quently, it is requisite to titrate the juices as soon as possible 
and in as nearly their original condition as possible in order to 
obtain results that are significant from a physiological standpoint. 
It is in these regards that many of the methods commonly em- 
ployed, no matter how useful they may be for some purposes, 
are not always available for the study of the activities of the living 
organism. For instance, the addition of alcohol, while it may 
serve to clear the juice for the purposes of titration, must un- 
doubtedly produce the esterification of some part of the acids. 
Similarly other chemical substances will not be without their 
effect in altering the original acidity. Besides all this, the time 
