648 



SCIENCE 



[Vol. LV, No. 1483 



writer has had occasion to make large numbers 

 of H-ion determinations, the gas-chain-electro- 

 metric method originally proposed by Hilde- 

 brand- and later modified for soil work by 

 Sharp and Hoagland,^ being employed.* 



As is widely known, the Rhode Island Sta- 

 tion has conducted several series of field plot 

 experiments representing different rotations 

 and various methods of fertilization, with but 

 slight change over a period of more than thirty 

 years. It is thus possible, by a proper choice 

 of plots, to secure field samples of surface 

 soils varying in Pjj from 4.4 to 7.8 with a 

 difference of but a few tenths of a Pj^ unit 

 between successive samples. The following 

 table presents data from such a series of sam- 

 ples, which are thought to be representative of 

 the plots sampled.^ The moist composite soil 

 samples in tight Mason jars were brought to 

 the laboratorj' immediately, rubbed through a 

 i4inch sieve, and the H-ion determinations 

 made the same day as collected. Column 2 in 

 the subjoined table presents the H-ion concen- 

 trations of these fresh soil samples. Portions 

 of these same samples were then air-dried in 

 the shade, and other portions oven-dried at 

 103° C. for a period of six hours. The last 

 two columns give the Pjj data secured from 

 these dried soils. 



The following conclusions may be drawn 

 from the accompanying figures. Drying acid 



2 Hildebrand, J. H., 1913, "Some Applications 

 of the Hydrogen Electrode in Analysis, E^search 

 and Teaching." Jour. Am. Cliem. Soc, 35, p. 

 847-871. 



3 Sharp, L. T., and Hoagland, D. E., 1916, 

 ' ' Acidity and Adsorption in Soils as Measured 

 by the Hydrogen Electrode." Jour. Agr. 'Res., 

 VII, p. 123-145. 



* The hydrogen electrode vessel was constantly 

 shaken during saturation by a device operated 

 by a small motor. This vessel carried two plat- 

 inized electrodes, thus permitting duplicate 

 voltage readings on the same solutions. This has 

 been found by the writer to be a necessary precau- 

 tion, as occasionally an electrode will ' ' go bad ' ' 

 in slight degree onlj', and if no check is available, 

 wrong results are unwittingly reported. Both 

 electrodes in all of the above-listed results gave 

 identical readings. 



" The soil of all the plots is classified by the 

 United States Bureau of Soils as Miami silt loam. 



H-ION (30NCENTEATI0NS OF FEESH 

 AND DEIED SOILS 



soils, either at room temperatures or at 103° C, 

 has but little effect on their H-ion concentrations 

 as subseqiiently detennined, although there ap- 

 pears to be a tendency toward slightly increased 

 acidity at the higher temperature in practically 

 every case. Drying alkaline soils, however, 

 i-enders them decidedly less alkaline (decreases 

 the OH-ion concentrations). This is especially 

 noticeable where a temperature of 103° C. is 

 used. In the case of soil 13, a decrease of 0.42 

 of a Pjj unit is recorded, while soil 14 shows a 

 decrease of 0.39 of a Pjj unit. In the ease of 

 an exactly neutral soil (No. 10), drying has 

 practically no effect. The reasons for these 

 differences are somewhat obscure, although 

 drying is doubtless accompanied by oxidation 

 which is in itself an acidic process. It should 

 be recalled that the soils in question are 

 granitic soils of high potential acidity. Dry- 

 ing, heating, or otherwise profoundly changing 

 them might conceivably present newly exposed 

 surfaces to the solvent, possibly by removing 

 certain enveloping colloidal materials of more 

 or less alkaline nature; the definite fracture of 

 certain of the mineral particles, thus directly 

 exposing freshly abraded surfaces to the 

 solvent is also by no means impossible. Fur- 

 ther work will be necessary to establish a 

 definite explanation. It is hoped that similar 

 data from soils of widely different genesis may 

 be forthcoming. 



Paul S. Burgess 

 Ehode Island Agbicultural 

 Experiment Station 



