344 



SCIENCE. 



[N.S. Vol. XVIII. No. 454. 



As au average of the thirty- two determina- 

 tions of NO3, SO,, HPO, and SiO^ made by 

 Mr. Belz, and of the CI and liCO^ made by 

 Mr. A. T. Strahorn, it was found that from 

 the oven dried samples we received 68.85 per 

 cent, more NOj, 62.38 per cent, more HCO3, 

 62.42 per cent, more HPO,, 24432 per cent, 

 more SO^ and 287.9 per cent, more SiO^ than 

 from the fresh field sample, but about the 

 same amount of chlorine in each set of deter- 

 minations. 



This year, early in June, Dr. Schreiner and 

 Mr. Ferris, of this Division, have shown by 

 a less extended series of observations that the 

 oven-dried samples yielded 54.15 per cent, 

 more calcium and 109.03 per cent, more 

 magnesia. 



We were led to make these observations on 

 account of the great difficulty in determining 

 the true amount of nitrates in soil samples, on 

 account of the rapid changes in nitrates which 

 occur after a soil sample has been taken, the 

 work being done to ascertain whether it would 

 be admissible to render the samples water 

 free to stop such action, and were surprised 

 to find- that we could recover from the oven- 

 dried samples more readily water soluble salts 

 of nearly every sort determined than we couH 

 recover from the fresh sample. The reasons 

 for this increased amount are discussed in a 

 section of the report of our results for 1902 

 not yet published. In this discussion we 

 assigned several causes, but regard the phys- 

 ical conditions produced by the drying as the 

 chief one. It appears to be demonstrated that 

 the strength of the soil solutions in the water 

 films surrounding the soil grains increases as 

 the surface of the soil grain is approached, 

 in an undetermined ratio; and when a moist 

 field sample is put into distilled water and 

 shaken for three minutes the films of water 

 which the soil grains and granules possess un- 

 der the field conditions move about in the so- 

 lution with the soil grains, and during the 

 three minutes of agitation, which we have 

 adopted as our practicable limit, only a portion 

 of the salts diffuse out into the surrounding 

 water; but when the soil sample is rendered 

 water free the readily water soluble salts are 



deposited on the surface of the soil grains 

 and the surface of the soil granules, so that 

 when the distilled water is dashed upon them 

 they go into solution; during the vigor- 

 ous agitation, they are carried bodily away 

 from the soil grains much more completely 

 during the three minutes than is possible by 

 the slower process of diffusion which must oc- 

 cur in the case of the moist sample, and on 

 this account we recover a larger per cent, of 

 the readily water-soluble salts which the soils 

 carry. 



There is still another physical condition 

 which makes it possible to recover a large 

 amount of readily water soluble salts by wash- 

 ing the oven-dried sample. In the first place 

 the soil granules are more completely broken 

 down by the pestling to which the samplr--. 

 are subjected after being oven-dried, so thai 

 the deposited salts are more freely exposed 

 to the water when it is put upon the samples, 

 and are dissolved more quickly on this account. 

 Further than this, while soil samples are dry- 

 ing in the oven the capillary action which is 

 set lip in the interior of the soil granules 

 brings out upon their surface a considerable 

 quantity of the salts, which in the moist condi- 

 tion are retained in the interior of the granules 

 where the diffusion outward would he neces- 

 sarily slower than if the granular condition 

 did not exist and the salts were all in the 

 water film surrounding the surface of the 

 compound grain. This capillary action there- 

 fore which takes place during the time of 

 drying, brings soluble salts where the water 

 comes quickly in contact with them, even 

 though the pestling does not completely break 

 down the granular structure, which, as a mat- 

 ter of fact, it never does. 



Large as are the amoiuits of readily water- 

 soluble salts which we are recovering from our 

 field samples, observations which we cite indi- 

 cate that the amounts actually present are 

 an undertermined amount greater than those 

 we have found. As an example of the 

 amounts of readily water-soluble salts which 

 field soils carry, and as an illustration of the 

 rapidity of securing results and the character 

 of the results, the following table is given, 



