322 BOTANICAL GAZETTE [ NOVEMBER 
the acid in aqueous solution of given concentration. That the 
great ionization often masks the effect of the increase in the 
toxic properties of the un-ionized part is easily understood when 
we recall that the toxic value of the ionized portion of an 
acid is not greater than the toxic value of the ionic H + the 
toxic value of the anion. 
Putting all together, we get in brief the following: (1) The 
replacement of one H in the acetic radical by Cl doubles the toxic 
properties of the un-ionized portion, and increases the ionization 
in a ~ solution from 2 per cent. to 20 per cent.; the resultant 
of these two factors is an increase in the toxic value of about 40 
per cent. in a ” concentration. (2) The replacement of two 
atoms of H by Cl more than trebles the toxicity of the un-ionized 
molecule and causes ionization to advance from 2 per cent. t0 
70 per cent. ina oa solution. This gives a net increase of about 
30 per cent. in toxic properties at this concentration. (3) a 
all three H atoms are thus replaced by Cl the un-ionized mo g 
cule has a toxic value of over five times its original value an 
ionization advances from 2 per cent. to 88.8 per cent. in a 558 
i ; : joniza- 
solution. At this concentration the effect of the greater ion : 
tion is more than can be made up by the increased toxic i 
ties of the 11.2 per cent. remaining in molecular form, hen 
4 : ; n ion as 
fall in the toxic properties of this acid at [3 concentratl 
compared with the original acetic. t in 
The values of the un-ionized molecules as worked i an 
table I, p. 325, show that these acids are very far from — 
exception to the rule that the toxic properties of ee 
increase with the introduction of Cl into the organi sa 
These values are as follows: 
+ 
Acetic acid, 2.8 times the value of ionic H. 
Monochloracetic acid, 4.7 “ ““ “ 
Dichloracetic acid, 9.5 “ “ " 
Trichloracetic acid, 14.1 r 
