IOWA ACADEMY OF SCIENCES. 
61 
percentage of phosphates should be regarded as abnormally 
low. 
In 1884, Stutzer^ endorsed the suggestion previously made 
by Tollens, of using a dilute solution of citric acid in place of 
the usual ammonium citrate solution, in estimating the avail- 
able phosphoric acid of fertilizers; claiming that thereby the 
actual manurial value was much better approximated than by 
the old method. He adopted and recommended a one per cent 
solution of citric acid. 
Later A. Thomson f endorsed Stutzer’s recommendation.. 
“Neither Stutzer nor Thoinson, however, appeared to give any 
reason for the strength of citric acid solution adopted, beyond 
the fact that the results obtained with a solution of this strength 
(one per cent), showed a fair correspondence with the compara- 
tive efficacy accredited by practical experience to the fertilizers 
examined.” Their suggestions related to the testing of fertil- 
izers, not soils. 
In A) arch of the present year Bernard HyerJ published the 
results of an extended investigation in which he applied to soils 
the method recommended by Stutzer for application to phos- 
phatic fertilizers. The soils with which he worked were those 
of the famous experimental barley plots at the Botham sted 
Experiment Station, England. 
In order to decide intelligently upon the strength of the 
citric acid solution to be used in the work. Dyer first made 
approximate determinations of the acidity of the rooi4-sap of a 
large number of plants, belonging to twenty different natural 
orders, and including most of the ordinary agricultural plants, 
garden vegetables, as well as field crops. From about 
100 determinations he obtained an average acidity of a trifle 
less than one per cent, calculated as crystallized citric acid. 
The average for 100 plants was .85 per cent. Averaged first by 
orders, the average of these averages was .91 per cent. Speak- 
ing of these sap-acidity determinations. Dyer says: “Obviously 
these determinations, numerous and laborious as they have 
been, can only be regarded as being in the nature of a tentative 
and preliminary enquiry of a very crude kind, if criticized from 
the botanical or physiological standpoint. But they appear to 
be sufficient to indicate that the ratio of the soluble free acid in 
*Chem. Ind. Feb., 1884. Quoted in Jour. Cli. Soc., 1894, p. 131. 
tChem. Ind., 1885. Quoted in Jour. Ch. Soc., 1894, p. 123. 
$ Jour. Chem. Society, London, March, 1894. 
