1915] ROSE—APPLE BARK 59 
(not allowing for increased ionization with dilution), H* concen- 
tration here would figure, not 2.0 times, but 2.4 times 107%, or 
10~*°?; that is, both indicator and titration figures show diseased 
bark to be less acid than healthy bark. With this in mind, a 
reference to tables I and II above shows that oxidation in the 
BUNZEL apparatus is in inverse ratio to the acidity of the solution 
being tested. 
This correlation between oxidation and acidity seems also to 
have obtained in REED’s work (3, pp. 56 and 76), though he fails 
to bring out the point, where juice of bitter rot apples caused 
greater oxidation than the juice of more acid healthy apples. The 
results obtained by BUNZEL (2, p. 26) in testing the effect of differ- 
ent concentrations of pyrogallol show that as the concentration 
decreased from 16 per cent to 1 per cent pyrogallol the negative 
pressure increased from 2.11 cm. of mercury to 2.86 cm. This 
may not be due to decrease in acidity, as determined by the pyro- 
gallol concentration (attention is not called to it in BUNZEL’s 
discussion of the table), but such an explanation seems the simplest 
and most likely. 
Titration and indicator tests on a.1 per cent solution of pyro- 
gallol and on a two-thirds of 1 per cent solution, the strength used 
in the apparatus if the diluent were only water, gave the results 
shown in table III. 
TABLE III 
RESULTS OF TITRATION AND INDICATOR TESTS WITH PYROGALLOL SOLUTIONS 
No. OF CC. OF N/20 gi ingen H+ conceNTRATION AS INDICATED 
SARY TO NEUTRALIZE I CC. OF ee ieee. GRANGE 
PYROGALLOL SOLUTION TO peanica eximaiane 
SOLUTION 
I per cent 2 of r per cent I per cent 3 of x per cent 
Re et Ot 0.13 0.086 <1073-33 10~3-33 
6 months old....... 0.34 0.23 3.50X10~3-33 | 2.33X107 3-33 
=107 2-79 =1I07?: 96 
The indicator figures for H* concentration of a fresh two-thirds 
of 1 per cent pyrogallol solution (about 1/20 molecular) agree well 
with those calculated from the electrical conductivity of such a 
solution. This is known to be 3.12 mu, whence the percentage dis- 
- Sociation=3.12+355 (u at infinite dilution)=o.88 per cent. If 
