I'J-'Ol SOILS — FERTILIZERS. 211 



Studios conducted at the New Jersey Experiment Stations on the Influence of 

 washed sand of four different degrees of fineness, and of very tine unwashed 

 sand, upon the reaction and concentration of a nutrient solution, are reported. 



The solution was applied to the sand in culture pots to give a moisture content 

 of GO per cent of the water-retaining capacity of the sand in every case. The 

 solution was renewed at stated intervals after as much as possible of the old 

 solution had been extracted from the sand by suction. Tests were made of these 



: solution samples for the hydrogen-Ion concentration and for the total salt con- 

 centration, and the results of these tests were compared with those of similar 



I tests of the original solution. • 



It was found that with the different grades of washed sand there was no 



1 evidence of the adsorption of salts or ions in sufficient amounts to alter mate- 

 rially either the reaction or the total salt concentration of the solution in contact 

 with the solid particles of the substrata. The adsorptive capacity of the un- 

 washed sand was sufficient to reduce the total salt concentration of the solution 

 from 1.76 atmospheres to 1.61 atmospheres (average reduction of 8.5 per cent) 

 during the first 24-hour interval. The reaction of the nutrient solution was not 

 markedly altered by contact with the unwashed sand. By renewal of the nutrient 

 solution the initial adsorptive effect of the unwashed sand was soon eliminated, 

 apparently by saturating its adsorptive capacity. The adsorptive properties of 

 ♦he unwashed sand appeared to be due to the very finely divided colloidal or 

 semicolloidal material which was removed from the sand in the process of 



I washing. 



! Colorinietric determination of hydrogen-ion concentration without buffer 



I mixtures, with especial reference to soils, L. J. Gillespie {Soil Sci., 9 (1920), 



; No. 2, pp. 115-136, fi(j. 1). — A simple technique as developed by the Bureau of 

 Plant Industry of the U. S. Department of Agriculture is described in full for 

 the preparation and use of a series of color standards for the colorinietric 

 determination of the hydrogen-ion exponent. No buffer mixtures are required. 



; From the method of calibration, however, any salt or protein errors will be 



j the same as if the measurement had been made witli the 0.05 M buffer mixtures 

 of Clark and Lubs. 



I Each color standard consists of two test tubes, one tube containing dilute 



j alkali and the other dilute acid. The tubes contain altogether 10 drops of 

 Indicator solution, the 10 being divided between the alkaline and the acid 



: tubes in various drop-ratios. A table is given containing all the necessary 



i data. 



I The method is based on a study of the nature of the color change of the 

 Indicators with change of hydrogen-ion exponent (pH). For all the indicators 



> selected the following equation, which comes from the mass action law, was 



1 found to hold within the experimental error of the color readings: pn=/i;+ 

 log (drop-ratio). The indicators studied are from the selection of Clark and 

 Lubs; and the values of the constant k of the equation, good to about 0.1 at 

 25-30°, are as follows : Bromphenol blue, 4.1 ; methyl red, 5 ; broracresol purple, 

 6.3 ; bromthymol blue, 7.1 ; phenol red, 7.7 ; cresol red, 8.1 ; and thymol blue 

 (alkaline range), 8.S. Soil extracts were prepared, water clear, by the use of 

 oolloidal iron solution. Measurement of the hydrogen-ion exponents of these 

 extracts (from nine soils only) gave the same results as were obtained by the 

 usual methods. Without further study, however, such use of colloidal iron 

 can not be recommended for general use. 

 A list of 22 references to literature bearing on the subject is Included. 

 The determination of ammonia in soil, D. J. Matthews (Jour. Agj: Sci. 

 [England], 10 {1920), No. 1, pp. 72-85, figs. 2).— A method and a so-called aera- 



I 



