So Brown , — On the Existence of a Semi-permeable Membrane 
These observations regarding the behaviour of the grain of the blue 
variety of H. vulgare when steeped in dilute sulphuric acid therefore 
indicated that water alone obtains entrance to the grain under these 
conditions if its coverings remain intact, and that consequently the coverings 
of the grain behave as a semi-permeable or selective membrane with regard 
to an aqueous solution of sulphuric acid. But as this conclusion was based 
solely on indications furnished by the colour reaction with acid of the blue 
pigment of the aleurone cells of the grain, it’was evidently desirable to test it 
by other methods of investigation. 
In further experiments grains of the blue variety of H. vulgare were 
steeped in a i per cent, solution of sulphuric acid for periods of time varying 
from 24 to 72 hours, and subsequently were cut — some longitudinally, and 
others transversely — into sections. On testing the reaction of these sections 
with a solution of methyl-orange no indication of the presence of free acid 
was obtained in any portion of the seed within the testa — the coverings of 
the grain, however, exhibited an acid reaction. In all the experiments the 
presence of water was demonstrated within the seed coverings, both by the 
swollen and soft condition of the endosperm and also by the turgid condition 
of the cells of the embryo. 
It was evident, however, that more conclusive proof that the coverings 
of the grain functioned as a semi-permeable envelope would be obtained, 
if, following steeping the grain in a solution of sulphuric acid, concentration 
of the solution of acid was demonstrated — for manifestly concentration 
must take place if water only is absorbed by the grain under these 
conditions. 
Experiments with barley grains, in which they were steeped in normal 
(4-9 per cent.) sulphuric acid, and the remaining acid solution was subsequently 
titrated with standard alkali, readily demonstrated that a marked con- 
centration of acid in the solution takes place under these conditions. But 
it appeared more satisfactory to establish, if possible, that the concentration 
which takes place is proportional to the volume of water abstracted from 
the solution of acid by the barley grains during steeping. 
The following experiment was made with this object in view. 10-899 
grms. of air-dried barley grains were in the first instance steeped in 15 c.c. 
normal (4*9 per cent.) sulphuric acid for 3 hours, and afterwards the grains were 
drained, well dried in filter-paper, and reweighed. The weight obtained 
was 12*509 grms. This preliminary treatment of the grain was carried on 
in the first instance to neutralize a feeble basic condition apparently 
natural to the skins of the grain, and secondly, in order to correct as nearly 
as possible for the weight of moisture adhering to the skins of the grain 
after draining and drying in filter-paper. 
Following this preliminary treatment the grain was again steeped in 
15 c.c. normal sulphuric acid and allowed to remain for 48 hours. 
