164 _ BOTANICAL GAZETTE [OCTOBER 
the “alkaline” end of the range, 1 cc. of 0.005 per cent (N/700) 
hydrochloric acid solution. 
The volume in all the tubes should be made up at once to 5 cc. 
The specific acidity values accepted for the several drop ratios are 
given in table II. This specific acidity is based on the H-ion concen- 
tration of pure neutral water as unity, as defined by WHERRY (10). 
The articles by WHERRY and Apams (11) and CLark (11) discuss 
this system of stating H-ion concentration. 
TABLE II 
SPECIFIC ACIDITY VALUES IN ROUND NUMBERS 
BROMPHENOL BLUE THYMOL BLUE, ACID RANGE 
Drop RATIO : se ha 
Specific acidity 5 Specific acidity Py 
» ry RE ea niabirts Nine ini Gea 6300 a4 400,000 1.4 
oo 4000 3.4 250,000 1.6 
yg Sue ee ere eae) Piak S) 2500 3.6 160,000 1.8 
Pha Uae eR AV eer gah 1600 2.5 100,000 2.0 
Lek ee Se Meg a mA I 4.0 63,000 2.2 
Gites eon oes Lee 630 4.2 40,000 2.4 
pt Sere Rey See era 4.4 25,000 2.6 
These specific acidity (and P,) values, while not absolutely 
exact, are close enough for the purposes of this investigation, particu- 
larly as it was found that the specific acidity of the sorrel extracts 
fell at the extreme acid end of the bromphenol blue series, or between 
that and the “alkaline” end of the thymol blue, acid range, where a 
close estimation is impossible.* The sorrel extracts, however, were 
checked up by comparison with the straight acid color of the first 
indicator and the straight “alkaline” end color of the thymol blue, 
acid range. 
The color standards are quite permanent, and if the tubes are 
stoppered and kept in the dark they may be used over a long period 
(4). The literature citations, particularly 3 and 4, contain details 
on the use of indicators covering Py values from 1.2 to 9.8. Both 
titrable and specific acidity were determined also on water 
§ As stated by GILLESPIE, measurements cannot be accepted at the point where 
the drop ratio is 9:1 or 1:9 (7:1 or 1:7), as the percentage transformation of the 
indicator is so nearly roo or zero that the Ht exponent may be far from that repre- 
sented by the ratio, and this would not be disclosed by a difference in color. 
