Notes. 
between P H 8-98-P H 7-88, and that the portions of the curve between P H 9-24-8-98 
and P H 7-88-6*77 have the same slope. It follows that if the same P H interval 
is used as standard in all measurements of respiration by this method the buffer action 
can be disregarded, provided that the same water is used for making up all the 
reagents: in which case only are all the experiments strictly comparable. If, how¬ 
ever, it is intended to test the effect of varying hydrogen-ion concentrations on 
respiration, care must be taken to choose P H intervals which represent equal amounts 
of work done (that is, C 0 2 evolved). These can readily be determined from the 
titration curve. The particular curve presented was developed to fill a practical need, 
and cannot be regarded as directly applicable to tap-water in other towns, but the 
method described is offered as simple, practical, and reasonably accurate. 
It is obvious that the same method can be used to determine the additional 
buffer action of reagents whose effect on respiration is being studied. In cases 
where there is marked buffer action it is necessary to adjust the standard interval to 
be used in determining the normal, so that the amount of C 0 2 required to produce an 
appreciable change in the P H of the reagent shall be the same as the normal amount. 
For example, if it requires 0-05 c.c. of the standard C 0 2 solution to change the P H of 
10 c.c. of tap-water from 7-60 to 7*36, and 0-5 c.c. C0 2 solution to change the P H of 
10 c.c. of the reagent by the same amount, then the standard must be taken as the 
change produced in 10 c.c. tap-water by 0-5 c.c. C 0 2 solution (in this particular case, 
Ph 8-51-7-24). 
Pj'ecautions. All glass used must be of the best quality. Pyrex glass is the 
best for all indicator work, but where unobtainable Jena glass makes a reliable 
substitute. All the glass used in these experiment^ was carefully cleaned with nitric 
and chromic acids, then boiled in three changes of distilled water, and finally rinsed 
with alcohol. The rubber tubing used for closing the titration tube was boiled 
repeatedly and sealed on to the glass with fresh unused paraffin wax (m.p. 52°). The 
colours were matched by daylight (north light) against an unglazed white paper. 
Conclusions. Tap-water shows a decided buffer action when titrated against 
a standard solution of carbonic acid. 
That this relation can be expressed in the form of a titration curve from which 
the change in hydrogen-ion concentration produced by equal amounts of C 0 2 
(produced in respiration or otherwise), at any point on the curve, can be deduced. 
The writer wishes to express her thanks to Professor W. Wright Smith, and to 
Dr. R. J. D. Graham, of the Royal Botanic Garden, for their kindness in providing 
facilities for these experiments. 
EDITH PHILIP SMITH. 
The Royal Botanic Garden, 
Edinburgh. 
References. 
1. Haas, A. R. C. (1916) : A Simple and Rapid Method of studying Respiration by the 
Detection of Exceedingly Minute Quantities of Carbon Dioxide. Science, xliv. 105. 
2. Palitzsch, S. (1916) : Uber die Anwendung von Borax und Borsaurelosungen bei der 
colorimetrischen Messung der Wasserstoffionenkonzentration des Meenvassers. Biochem. 
Zeit., lxx, 333. 
