626 EMERSON: BLACKENING OF BAPTISIA TINCTORIA 
the temperature at which the change to the inactive modification 
takes place.’’ He then gives destruction temperatures for several 
oxidases in various plants, which vary from 60° to 95° C. 
Citric acid tests — Ten cubic centimeters of the enzyme solution 
were put in tubes, then by means of a burette I cc., .5 cc., and 
.2 cc. of citric acid of different strengths were added, the tubes set 
aside for an hour and then tested with the solution of gum guaiac 
and hydrogen peroxide. Citric acid (normal) was used to begin 
with, then one fourth normal, one eighth normal and one sixteenth 
normal, each one tried in three tubes with the three different 
amounts of acid. The normal solution gave no result at all, ex- 
cept a heavy brown precipitate. 
The quarter normal, when only two tenths cubic centimeters 
were added, gave a weak guaiac reaction and a gray-blue peroxide 
coloration. 
With one half a cubic centimeter of the one eighth normal 
solution there was a fair reaction with both, but not normal in 
color, the good colors being reached only with .2 cc. of the one 
sixteenth normal solution. In all but the last there was a precipi- 
tate ; in the stronger solutions this was brown, in the weaker blue, 
and in most the color faded. No definite conclusions could be 
drawn from these results. 
Sodium hydroxide tests. —These were made in the same way 
as those with citric acid: a one quarter normal solution was the 
strongest used (ten grams in one litre of water), the weaker ones 
being one quarter, one eight and ore sixteenth of that. Results 
follow : 
One quarter normal—no reaction with either guaiac or hy- 
drogen peroxide, a clear yellow liquid. 
;i; normal, giz normal, gy normal 
(to cc. {normal and 3o ce. (5 cc. }normal and 35 cc. (24 cc. } normal and 37% 
H,0. fh ec. HQ, 
in a few cases gave Most of these experi- All gave guaiac reaction, 
a slight reaction to guaiac, ments gave a guaiac reac- though greenish instead of 
none to H,O,. .2 cc. and tion, but none with H ,O, blue, and with .5 an nd .2 cc. 
less gave generally a guaiac until only .2 cc. was used. there was a reaction to 
reaction, occasionally one H,0,, though green instead 
with H,0,. of blue. 
The sodium hydroxide solution gave a yellow color to the 
