74 
F. STOWARD, D.SC, : 
ment clear and at the same time afford evidence of a tangible 
kind from which certain deductions may be drawn. 
If tubers are steeped in a solution of 10% sulphuric acid 
for varying periods of time, and the amounts of acid present 
at the commencement and termination of the experiment 
are determined in a given volume of the solution, the re- 
lative amount of acid absorbed by the steeped tuber may 
be estimated by noting the decrease in the amount of acid 
in the external solution. Examples of such experiments are 
given below : — 
Expt. 1. 
Grams of acid per 1 00 c of solution 
Decrease in 
Duration 
at commence* 
at the 
amount of 
of 
ment of 
termination 
acid per 100 cc 
immersion. 
steeping. 
of 6 teeping 
solution. 
A. 
2i hours 
9.506 
9-403 
0.098 grams 
B. 
4 .» 
9.408 
9.408 
0.00 
C. 
20 „ 
9.408 
9-359 
0.049 
From the above data obviously the amounts of acid 
which diffuse from the acid solution into the tubers are 
relatively minute, and we may hazard the suggestion that 
just as in the experiments with salt solutions, the acid is 
not freely absorbed by the tuber. If we know the weight 
of the tubers taken and the volume of acid solution used in 
each of these experiments, then together with the above 
determinations we have all the necessary data for calculating 
the apparent percentage weight of acid absorbed. Taking, 
for example, experiment (A), we have weight of acid with 
drawn from 1500 cc of solution = 15 x 0.098 grams, and 
weight of tubers = 1650 grams, whence the percentage of 
acid apparently present in the tubers equals 
15 x 0.098 x 100 
= 0.089% 
1650 
The foregoing statement implies that the distribution 
of the absorbed acid is uniform throughout the substance of 
the tuber, but, as we shall see presently, this is not correct. 
We may, however, defer consideration of this point to a 
later stage. 
Quite similar results follow on steeping intact tubers 
in solutions of boracic acid, although it is to be noted that 
this compound differs from sulphuric acid in certain im- 
portant respects both as regards its chemical and physico- 
chemical properties. The impermeability of the skin of 
the tuber to boracic acid is, to take an example at random, 
shown by the results of the following experiments : — Two 
lots of tubers were separately steeped in boracic acid solu- 
tions of (a) 1.61 and ( b ) 0.63% strengths for 10 and n days, 
respectively. Determination of the amounts of boracic acid 
in definite volumes of solution at the commencement and 
