362 Stiles and J0rgensen.—Studies in Permeability. I. 
in Fig. 12. It will be observed that as ferric chloride is added to the copper 
sulphate the conductivity of the solution is lowered as in the case of 
mixtures of copper sulphate and aluminium chloride, but in a very much 
more marked degree. 
A fact which should be mentioned here is the production in the 
solutions containing plant tissue of an orange-yellow precipitate, presumably 
of ferric hydroxide, whereas in the control solutions of the same original 
composition, but without potato, no such precipitation takes place. 
From these results one is at once led to inquire whether the formation 
of hydrochloric acid has anything to do with the form of the curves. 
We note a continual decrease in conductivity of the experimental solu¬ 
tions containing much iron, whereas the conductivity of the control increases. 
The result would be explained if the hydrogen ion were absorbed by the 
plant almost as fast as it is formed, or at any rate very rapidly. 
Series 13. In order to test this supposition, solutions of hydrochloric 
acid were used, potato discs constituting the tissue employed. It was 
found that a rapid fall in conductivity took place in all the concentrations 
used to - —A. The curve for the case of —HC 1 is shown in 
v ioo i6qoo / 1000 
Fig. 13 - 
Other acids yield similar results. The rapid fall in conductivity of the 
solution seems therefore due to the rapid absorption of the hydrogen ion by 
the plant tissue. 
