THE INFLUENCE OF CERTAIN ADDED SOLIDS UPON THE 
COMPOSITION AND EFFICIENCY OF 
KNOP'S NUTRIENT SOLUTION 
E. H. Toole and W. E. Tottingham 
It was pointed out many years ago by Nageli (i) that such insoluble 
substances as filter paper and parafiin shavings have the power of 
rendering water from a copper still suitable for the culture of algae. 
This observation led True and Oglevee (2) to make a study of the 
effect of these and other similar substances on the growth of plants in 
various solutions, the toxicity of which had previously been deter- 
mined. They found that solutions of copper sulfate, silver nitrate, 
and other substances, in concentrations near their toxic limits, were 
rendered markedly less toxic or even stimulating to lupine radicles 
when accompanied by such substances as shredded filter paper, freshly 
prepared potato starch and fine sea sand in amounts equal to about 
one thir^d that of the culture solution. These authors comment on the 
adsorbing power of soils and its relation to plant growth. 
Breazeale (3) studied the question from another angle. To soil 
extracts which supported but a poor growth of seedlings were added 
such substances as washed carbon black, calcium carbonate, ferric 
hydrate, aluminum hydrate, and quartz flour. Ferric hydrate was 
especially effective in causing an increased development of the roots of 
wheat seedlings. It was also found that these solids have a remarkable 
power of suppressing the toxic properties of distilled water. Parker (4) 
has measured the power of soils to adsorb salts from solutions and 
found not only that the concentrations of salts may be changed, but 
also that there is selective adsorption of certain ions from the solution. 
Consideration of these and related observations led the writers to 
investigate the effects upon the physiological balance of a nutrient 
solution, of various added solids supposed to offer relatively large 
presentations of surface. It was deemed possible that, if changes in 
the solution occurred under these conditions, the evidence obtained 
might render possible a distinction between adsorptive effects and 
ordinary chemical reactions, as causal agents. Rather unsuspected 
452 
