May 16, 1921 
Respiration of Sweet Potato Storage-Rot Fungi 
213 
ture growing on Irish potato cylinders or stems of Melilotus alba Desr. 
Before the culture flasks were inserted into the apparatus, air was pulled 
through the series of trap bottles and cylinders for about one hour to 
make sure (i) that all of the C 0 2 was being removed from the incoming 
air and (2) that there was no leak through the connections. 
At the termination of each experiment the mycelium was filtered into a 
tared alundum crucible washed with distilled water and dried to constant 
weight in a vacuum oven at 6o° C. The percentage of glucose present 
in the control as well as that remaining in the two culture flasks was 
determined by a Fric saccharimeter, from which the total amount re¬ 
duced was calculated. The culture and control flasks were weighed at 
the beginning and at the close of the experiment, and from these data 
corrections were made for loss of water due to evaporation or other 
causes. 
determination of co 2 
The fungi differed markedly in the rapidity at which they grew in the 
culture solution. Some of the organisms, as Rhizopus tritici y for example, 
grew rapidly from the outset, and C0 2 was evolved in from two to three 
days. Some of the other fungi, on the other hand, grew slowly and gave 
off no C 0 2 for a week or more. As soon as a precipitate appeared in the 
Ba(OH) 2 solution the C 0 2 was determined for each 24-hour period there¬ 
after to the end of the experiment. 
In the determination of the C 0 2 evolved the excess Ba(OH) 2 was 
neutralized by the addition of hydrochloric acid (HC 1 ), with the use of 
thymol blue (thymol sulphonphthalein) as an indicator. The precipitate 
(BaCOg) was then dissolved by adding an excess of N/i HC 1 . After the 
total volume of the solution had been determined, an aliquot portion 
(usually 25 cc.) was titrated against N/10 sodium hydroxid (NaOH) with 
brom phenol blue (tetra bromo phenol sulphonphthalein) used as the 
indicator. The number of cubic centimeters of N/10 NaOH used to 
neutralize 25 cc. of the solution was multiplied by the total volume of 
solution, which gives the equivalent of the excess acid. The excess acid 
was then converted into its equivalent of N/i HC 1 , and this amount was 
deducted from the total number of cubic centimeters of HC 1 required 
to dissolve the precipitate. The figure thus obtained was multiplied by 
the factor 0.022, the equivalent in C 0 2 of 1 cc. of N/i HC 1 . 
In the preliminary experiments the two indicators, phenolphthalein 
and methyl orange, usually used in titrations of this nature were tried, 
but neither gave a satisfactory end point. Scales ( 18) experienced like 
difficulties in titrations of a similar kind and found that thymol blue 
and brom phenol blue both had a very sharp end point. Thymol blue 
in the presence of Ba(OH) 2 and BaC 0 3 gives a brilliant blue color, which 
changes to a muddy green at the neutral point, to a lemon-yellow in a 
slight excess of acid, and to a pink in a strong acid solution. Upon the 
