[Vor. 7 
302 ` ANNALS OF THE MISSOURI BOTANICAL GARDEN 
cultures were removed to a culture chamber, and definite amounts 
of sterile acid and alkali were added by means of sterile gradu- 
ated pipettes. The final volume of each culture was 50 cc. 
and represented a dilution of the constituents comparable with 
that in the original nutrient solutions. The solutions were 
allowed to stand for 24 hours in order to reach a state of equili- 
brium, and, at the expiration of this period, H-ion determinations 
were made according to the colorimetric method of Clark and 
Lubs (717), all determinations being made at room temperature. 
(See figs. 1-5 and tables 1-11). 
Due to the presence of color in the beet decoction and in the 
peptone solution, it was necessary to use a colorimeter for the 
H-ion determinations. A Duboscq type was used in this par- 
ticular work, the detailed method of which has been described 
by Duggar (719). 
In all of the mineral salt solutions, a certain amount of pre- 
cipitate occurred upon the addition of alkali, the amount in- 
creasing with increase of added alkali. No such phenomenon 
was evidenced in the alkaline cultures of the beet decoction 
or of the peptone solution. The precipitation referred to com- 
menced with culture No. 29 in Pfeffer’s solution, No. 27 in Rich- 
ards' solution, and very faintly in No. 23 of Czapek's solution. 
On the other hand, there was no precipitation whatever in the 
acid cultures of any of the various media. 
As the reaction of the beet decoction passed from acid to 
alkaline, there was noted a decided color change from pale 
yellow to amber, and a slight cloudiness was perceptible begin- 
ning with culture No. 42. 
The titration eurve obtained with 2 per cent bacto-peptone 
agrees closely with the curves obtained by Clark and Lubs (17) 
with Witte peptone, falling, as one would expect, between the 
curves representing concentrations of 1 and 5 per cent. 
The initial P, of the original culture solutions varied, varia- 
tions of several tenths not being infrequent despite the most 
careful technique during preparation and the use of highest 
purity chemicals. Since the highest purity mono-basie potas- 
sium phosphate obtainable had a very high acidity due to the 
impurities present, the salt was recrystallized until the Sórensen 
coefficient of Py 4.529 for a 1/15 molecular solution was ob- 
tained. 
