MAcNIDER ON SOIL SAMPLES FOR CHEMICAL ANALYSIS. 447

When a starch is hydrolyzed with an acid, there is, of course, always the danger of converting a part or all of the pentosans, cellulose and allied bodies into sugars. Again the r8le played by diastase upon starch has not been settled. If, however, the analyst is content in reporting 6 . 2 j tinies nitrogen as protein, the ether extract as fat, and the residue obtained after boiling the ether-ex- tracted material with acid and alkali as crude fiber, then on equally good grounds he should be content in reporting starch as obtained by acid hydrolysis.

CHEMICAL LABORATORIES, WASHINGTON STATE EXPERIMENT STATION,

PULLMAN, WASHINGTON.

THE PREPARATION OF SOIL SAMPLES FOR CHEMICAL ANALYSIS.

By G. M. MACNIDER.

Received March 15, 1909.

The following investigation was undertaken to determine the proper sized sieve to use in pre- paring soil samples for chemical analysis when the total amount of plant food elements are to be determined. When the available or soluble plant food is determined, by the Official Method of the Association of Official Agricultural Chemists or by some other method using some solvent to abstract the plant food, a preparation using a sieve with perforations smaller than 2 mm. in diameter seems to be adequate, as i t has been shown by several investigators that the greater portion of the soluble plant food is found in the smaller par- ticles of the soil, i.e., the very fine sands, silt and clay. The Official Method of preparation has, however, been recently changed from 0.5 mm. sieve to I mm. sieve.

The size of sieve to be used, which is to determine what portion of the soil shall be taken for analysis, is of course an arbitrary standard. In making total analyses it is very necessary that the standard adopted be such that the analyses will give the fairest idea of the plant food contained in the soil. With some very coarse soils even the z mm. prepa- ration excludes from the analysis particles which i t would seem should be included. From the data here presented and from a large number of chemical analyses of soils made in this laboratory we have arrived a t the conclusion that the most satisfactory method of preparation, when the total plant food constituents are to be determined, is to pass the

U. S. Debt. of A g r , BUT. of Chem., Bull. 107 (revised).

sample through a sieve having circular perforations 2 mm. in diameter and take the portion passing the sieve as the “fine earth” which is to be analyzed and to regard the portion not passing the sieve as coarse gravel which should not be classed as “fine earth’’ or soil. This method also gives a uniform preparation for both the chemical and mechanical analyses.

The method of preparation is as follows: Spread the sample on a board covered with

heavy paper and roll with a wooden rolling pin to break up lumps. The sample is then passed through a sieve having circular perforations z mm. in diameter. If there are any coarse particles they should be put in a mortar and rubbed with a rubber- tipped pestle to remove the adhering, fine particles. This operation should be repeated till the coarse particles are clean. When all the fine particles have been passed through the sieve the sample should he thoroughly mixed before the portion for analysis is taken out. I n some samples the large particles passing the z mm. sieve may be large enough to interfere with the fusion in the analysis. In such cases a portion may be pul- verized for the determinations requiring fusion.

In the following table are analyses of represen- tative soils made on the 0.5 mm. preparation and on the z mm. preparation. The 0.5 mm. was taken for comparison as this was for a number of years the official method of preparation of soil samples and a large number of analyses have been made in this laboratory on that preparation. The table shows the percentages of plant food constitu- ents and the pounds per acre of each constituent to a depth of 8 inches, calculated from the apparent specific gravity, also the apparent specific gravity and the per cent. of fine soil passing the sieve in each preparation. The samples have been selected so as to represent a large variety of soils in North Carolina, the sands and sandy loam soils of the Atlantic Coastal Plain, the coarse sandy loams of the Piedmont Plateau and the sandy loams of the Mountain Region. Comparative analyses were not made of the clay and loam soils as practically all of these pass the 0. j mm. sieve.

DISCUSSION OF RESULTS.

Reference to the table will show the differences in the analyses so that i t is only necessary here to point out a few of the more marked differences.

1 The method of mechanical analysis in use in this laboratory is See Bull. 24, Bwr. o f Soils, the same as that used by the Bur. of Soils.

by L. J. Briggs.

448 THE JOURNAL O F INDUSTRIAL A N D ENGINEERING CIIEMISTR Y . July, 1909

The most marked differences to be noted are in the percentages of soil passing the different sieves and in the percentages of potash and lime. There are also differences in the percentages on nitrogen and phosphoric acid, but as the nitrogen is de- rived from organic sources and the phosphoric acid also to a large extent, the differences are not so marked.

The coarse particles from all the samples were examined microscopically to determine what niin- erals were present, so that this could be taken into consideration in interpreting the analyses.

Nos. 287 to 649 inclusive are residual soils from the Piedmont and mountain regions, derived from granitic rocks.

In No. 287 only 45.9 per cent. of the sample passed the 0.5 mm. sieve, while 92.1 per cent. passed the 2 mm. sieve. The per cent. of potash is 4.17 on the 0.5 mm. and only 2.14 on the 2 mm. The difference in the per cents. of lime are also marked on this sample, being 0.37 on the 0.5 mm. and 0 . 0 7 on the 2 mm. The microscopic examination of the coarse particles from this sample showed them to be mostly quartz with some orthoclase. The chemical analysis of the coarse particles be- tween 0.5 and 2 mm. showed 0.3 per cent. potash. The subsoil of this sample No. 288 shows about the same differences.

With Nos. 289 and 290 a slightly larger amount of soil passed both the 0.5 and 2 mm. sieves. The differences in the percentages are equally as marked as in the preceding samples.

In No. 639 73.5 per cent. soil passed the 0.5 mm. sieve and 87.3 per cent. passed the 2 mm. sieve, the difference being much less marked than in the preceding samples. The difference in the percentages of potash and lime are very slight, 4.26 per cent. potash on the 0 .5 mm. and 4.00 per cent. on the 2 mm.; 0.30 per cent. lime on the 0.5 mm. and 0.31 per cent. on the 2 mm. The microscopic examination of the coarse particles showed them to be quartz with considerable amount of feldspar, which accounts for the percentages of potash and lime remaining practically the same on both preparations. This is in marked distinction to the preceding samples where the coarse particles were made up almost entirely of quartz and the differences in the percentages of potash and lime on the two preparations very marked. With the subsoil of this sample No. 640 the coarse par- ticles contained considerably less potash feldspar,

D A Y A N D GILPIN ON CRUDE PETROLEUM. 449

hence the difference in the per cent. of potash on the two preparations.

Nos. 648 and 649 show quite similar results to No. 639 both in the percentages of fine soil passing the sieves and in the percentages of potash.

Nos. 750 to 844 inclusive are representative samples of the coarser soils of the Atlantic Coastal Plain. The differences in the percentages of soil passing the two sieves are very similar, all or practically all of the sample passing the z mm. sieve and only from 59.6 to 88 . j per cent. passing the 0.5 mm. sieve. The difference in the per- centages of potash are also very similar, i. e . , the per cent, being considerably lowered when more of the sample is analyzed on the 2 mm. preparation than on the 0.5 mm. The microscopic examination of the coarse particles from these samples showed them to be composed almost entirely of pure quartz.

From the table and microscopic examinations i t will be seen that the greater portion of the plant food is found in the soil particles less than 0.5 mm. in diameter, that is. the particles between 0.5 and z mm. in diameter are composed chiefly of quartz, the exceptions to this being the samples in which there was only a slight difference in the analysis on the two preparations and the niicroscopic examination of the coarse particles showed them to contain considerable amounts of feldspar.

If we assume that the particles of soil less than z mm. in diameter fairly represent what should be termed the soil from which the plant derives its food, it is evident that in making determinations of the total plant food, the analysis if made on a sample prepared through a sieve with perforations less than z mm. in diameter, i. e., 0.5 mm., will show the soil to contain considerably more plant food than the soil from which the plant must derive its food and hence does not fairly represent the composition of the soil.

I\-ORTH CAROLINA DEPARTMENT OF AGRICULTURE, DIVISION O F CHEMISTRY.

THE CHANGES IN CRUDE PETROLEUM EFFECTED BY DIFFUSION THROUGH

CLAY. B y DAVID 'I'. DAY AND J. ELLIOTT GILPIN.

Received May 3 , 1909.

That the process of diffusion throughlclay and shale and the replacement by water have been important factors in the concentration of petroleum in certain places was pointed out by Day in 1 8 9 7 ~

Proc. Amer. Philos. SOC., Vol. XXXVI, No. 154.

and is shown very clearly by recent work of Gilpin and Cram.' Suppose, for example, the petroleum formed in the deeper portions of the earth finds access through a seam or other opening to a layer of fine-grained clay or shale. It will diffuse through the material if the latter is finely divided, but would be stopped by material too coarse for capillary diffusion. These authors have found that the oil will rise in tubes packed with fuller's earth and in so doing is partly fractionated. By using several tubes and uniting oils of the same specific gravity, oil of different grades can be collected in sufficient quantity to be fractionated again, and the process can be continued until oils are obtained which are not altered by further passage through tubes filled with fuller's earth.

If such a diffusion took place in a large mass of clay no accumulation of oil would be found a t any one spot, and a well drilled in this material would show only a small percentage, say 5-10

per cent., of petroleum. If now, as has been shown by Gilpin and Cram, water, either surface or sub- terranean, comes in contact with this clay i t will diffuse into it and displace 213-314 and perhaps, in long geological periods, even more of the petro- leum.

If the water surrounds the mass of clay the oil cannot escape and is driven finally into the coarse adjacent layers such as sandstone and gravel. The oil will remain in this position as i t cannot be displaced by any capillary action of water on the rock.

The pressure under which i t could accumulate would be entirely independent of hydrostatic pres- sure, and pressures equivalent to those observed in the phenomenon of osmosis can be brought about without an amount of water more than sufficient to saturate the clay itself-practically an infinitely smaller amount of water than is required for producing hydrostatic pressures equiv- alent to the pressures found in oil wells. These pressures are usually from jo to 300 fis. to the square inch-clearly within the range of osmotic pressure.

Pressures as high as Ijoo fis. per square inch have been claimed for natural gas, but i t is not to be supposed that all accumulations of oil and natural gas are attributable to the phenomena here under consideration. The various conditions of accumulation of petroleum, howevei, are so easily explained by the driving out of oil by water,

1 Amer. Chem. Jr., 40, 495.