Chapter V: Introduction (4)

Samples to determine the amount of empty space in a soil are taken as follows: The sampler is a piece of brass cylinder about nine inches long and about 1½ inches in diameter. A piece of clock spring is soldered in one end and sharpened to give a good cutting edge. This arrangement permits the sample to pass into the cylinder without much friction. The area enclosed by the clock spring is accurately determined and a mark is placed in the cylinder six inches from the cutting edge. The cylinder is driven into the soil to a depth of six inches, a steel cap being used to prevent the hammer from injuring the cylinder. The earth is next removed from about the cylinder with a trowel, and the separated cylinder of earth is cut smoothly off by a sharp knife and removed together with its brass envelope. The sample is taken to the laboratory in a cloth bag, dried and weighed.

=65. Taking Samples for Moisture Determination.=—A number of brass tubes is provided nine inches long and ¾ inch in diameter and with a mark six inches from the bottom.

The tube is pushed down into the soil to the mark and the sample of soil removed with the tube. There is but little danger of the sample dropping out of the tube even in sandy soils. When the tube is withdrawn each end is capped with a rubber finger tip making a perfectly air tight joint. The tubes containing the samples can be kept several days with no fear of losing moisture. This method is especially useful in having samples taken by observers in different localities who can enclose the tubes in a cloth sack and send them to the laboratory by mail daily or at stated intervals. A tube of the size given holds about fifty grams of soil.

=66. Taking Samples to Determine the Permeability of Soil to Water or Air.=—Whitney[49] determines the permeability of soil or subsoil to water or air in the following manner:

An excavation two feet square and eighteen inches deep is made in the soil. On one side of this hole the sample of soil or subsoil is taken by means of a narrow saw blade and a sharp carving knife. The sample of soil taken should be two inches square and 3½ to 4 inches long.

It is placed in a brass cylinder three inches long and 3¼ inches in diameter. The open space in the cylinder is filled with paraffin heated just to its melting point. As the paraffin cools the upper surface should be kept stirred to prevent the mass when set from receding from the square column of soil. Care must be taken to keep the paraffin from the ends of the soil columns and these should be left, as far as possible in their natural condition.

The rate of percolation of the water may be determined at the time the sample is taken. For this purpose an additional section of brass tube two inches deep is secured to the one holding the sample by a rubber band. An iron rod is driven into the earth carrying a retort stand ring supporting a funnel filled with fine gravel. The lower end of the soil column in the brass cylinder is placed on this gravel. Water is next carefully poured upon the top of the sample of soil being careful not to disturb the surface. The surface of the sample may be protected with a little fine sand. The water should be poured on the paraffin thus affording an additional protection to the soil surface. When the water begins to drop from the funnel a graduated glass is set under it and the time required for a given volume to pass through under an initial pressure of two inches is noted. The volume required represents one inch in depth over the four square inches of soil surface, _viz._: four cubic inches.

=67. Sampling of Soil for Staple Crops.=—Some variations from the usual methods are recommended by Whitney when the samples are taken from fields growing staple crops.

The immediate object of the work, for which these samples are desired, is to make a thorough study of the physical and chemical properties of a number of typical soils adapted to the different staple crops, such as grass, wheat, truck, and the different types of tobacco. They should be taken for a careful study of the texture of the soils, the relative amount and arrangement of sand and clay, the relation of the soils to moisture and heat, and the ease with which they can maintain a proper water supply for the different staple crops under existing climatic and cultural conditions. The ultimate object of such a study is to see how these conditions can be changed so as to make the soils more productive, and make them yield a better quality of crop, or to change the conditions in other soils, which differ from these, so that the culture of the different staple crops can be extended over wider areas by improved methods of cultivation and manuring.

The soil selected for sampling for these investigations should be typical, should represent fairly well a considerable area of land. It should represent either the very best type of land for the staple crop or crops of the locality, or the very poorest lands for these same crops. Both of these extremes are desired for contrast. For example, if the staple crop of the locality is wheat or a certain type of tobacco, select the soil best adapted to this staple crop, and another soil, if possible, in the same locality, representing considerable area of land upon which this staple crop cannot be successfully grown on account of the inferior yield, quality, or the time of ripening of the crop. The soil sampled should be, or should recently have been, under actual cultivation in the crop or crops best adapted to it, so that the real agricultural value of the land can be accurately known.

The samples should be taken inside the field, some distance away from fences, roads, or trees. If there are plants growing in the field, the sample should be taken about midway between two plants. The samples should be taken where they will typify fairly well the average soil of the field and of the large area of land which they are to represent.

The samples are taken in some one of the ways described herein. Each sample should be carefully labelled at the time of taking. The following blank form will be found convenient for this purpose:

│Locality:
LABORATORY No.: │
────────────────────────┼──────────────────────────────────────────────
No. of sack: │Description: (virgin or cultivated).
│ (_a_) Natural herbage:
│ (_b_) Crops best adapted to land (grass,
│ wheat, tobacco, truck, barren).
│ „
------------------------│ „
Date: │ „
│ „
------------------------│ „
Collector: │ „
│ „
------------------------│------------------------
Depth of sample: │
(Soil or Subsoil?) │Geologic formation:
... in. to ... inches. │

=68. Method of the Royal Agricultural Society.=[50]—Have a wooden box made, six inches long and wide, and from nine to twelve inches deep, according to the depth of soil and subsoil in the field. At one of the selected places mark out a space of twelve inches square; dig around it in a slanting direction a trench, so as to leave undisturbed a block of soil, with its subsoil, from nine to twelve inches deep; trim this block to make it fit into the wooden box, invert the open box over it, press down firmly, then pass a spade under the box and lift it up and gently turn it over.

In the case of very light, sandy, and porous soils, the wooden box may be at once inverted over the soil and forced down by pressure, and then dug out.

Proceed in the same way for collecting the samples from all the selected places in the field, taking care that the subsoil is not mixed with the surface soil. The former should be sampled separately.

In preparing the plot for the gathering of the sample, take care to have it lightly scraped so as to remove any débris which may be accidentally found there.

The different samples thus procured are emptied on a clean, boarded surface, and thoroughly mixed, so as to incorporate the different samples of the same field together. The heap is then divided into four divisions, and the opposite quarters are put aside, taking care to leave the two remaining ones undisturbed; these are thoroughly mixed together, the heap divided into quarters, and the opposite ones taken away as before. This operation of mixing, dividing into quarters and taking away the opposite quarter is continued until a sample is left weighing about ten or twelve pounds.

Thus is obtained the average sample of the soil. Of course where only a single sample is taken from the field this method of quartering is not resorted to, but the bottom of the box is nailed directly on and sent to the laboratory, where the soil is to be analyzed.

=69. Grandeau=[51] suggests that in taking soil samples there are two cases to be considered; first a homogeneous soil and second, a soil variable in its appearance and composition. First, if the soil is homogeneous, being of the same geologic formation it will be sufficient to take a mean sample in accordance with the following directions:

The field is first divided by diagonals or by transverse lines the direction of which need not be fixed in advance but as inspection of the form and configuration of the field may indicate. In the ordinary conditions, of homogeniety (marly, granite, argillaceous or silicious soils) it will be sufficient to select about five points per hectare from which the samples are to be taken. These points having been determined the surface is cleaned in such a way as to remove from it the detritus which may accidentally cover it; such as dry leaves, fragments of wood, foreign bodies, etc. The surface having been prepared, (five to six square meters) a hole is dug four-tenths of a meter long and as wide as the spade employed. The sides should be as nearly vertical as possible. As to depth it varies with the usage of the country in regard to tillage. The layer of arable earth is what in effect properly constitutes the soil. It ought not to be mixed with any fragments of the subsoil. When the hole is properly cleaned the samples are secured with a spade from the sides of the excavations. About five kilograms are taken. The soil is placed in a proper receptacle as it is removed from the hole.

This operation is repeated on as many points as may be necessary to obtain a mean sample of the soil of the whole field.

All the samples are now collected on a table sufficiently large, and intimately mixed together. Two samples, each of about five kilograms, are then taken from the mixed material. One sample is immediately placed in bottles and carefully stoppered and sealed; the other is dried in the sun or on the hearth of a furnace. When sufficiently dry the second sample is also placed in bottles and well stoppered. While mixing the samples, pebbles, etc., of the size of a nut and larger are removed, the weight of the rejected matter being determined. The nature of the pebbles should also be noted; whether silicates, limestone, etc.

The sample of subsoil is taken in exactly the same manner, using the same holes from which the samples of soil were taken. The nature, the arrangement and the appearance of the strata will indicate the depth to which the subsoil should be taken. In general, a depth equal to that of the sample of soil will be sufficient. The depth to which the roots of cultivated plants reach is also a good indication in taking a sample of the subsoil. In forests the sample of subsoil should be taken from four to five-tenths of a meter below the surface.

If the soil in respect of its geologic formation, its fertility or its physical aspect presents great differences, special samples should be taken in each part in accordance with the directions given above.

=70. Method of the Official Agricultural Chemists.=—In the directions given by the Association of Official Agricultural Chemists[52] it is stated that the soil selected should be as far as possible in its natural condition, not modified by recent applications of manure, or changed by the transporting action of water or wind. Surface accumulations of decaying leaves, etc., should be removed before taking the sample.

To eliminate accidental variations in the soil, select specimens from five or six places in the field which seem to be fair averages of the soil, remove two or three pounds of the soil, taking it down to the depth of nine or ten inches[53] so as to include the whole depth. Mix these soils intimately, remove any stones, shake out all roots and foreign matter, and dry the soil until it-becomes friable.[54] Break down any lumps in a mortar with a wooden pestle, but avoid pulverizing any mineral fragments; pass eight to ten pounds of the soil through a sieve, having circular perforations one twenty-fifth of an inch in diameter, rejecting all pebbles and materials too coarse to pass through the sieve. Once more mix intimately the sifted soil. Expose in thin layers in a warm room till thoroughly air dry (or dry it in an air-bath at a temperature of 40°), place six to eight pounds in a clean bottle, with label of locality and date, and cork the bottle containing the soil, for analysis.

The soil is rapidly dried to arrest nitrification; it is not heated above 40° lest there should be dissipation of ammonia compounds, or a change in solubility. The normal limit to which the soil may be heated in place by the sun’s rays should not be exceeded in preparing a sample for an agricultural chemical analysis.

The relative amount of fragments too coarse to pass through the sieve should be made a matter of record. They are soil material, but not yet soil, so far as agricultural purposes are concerned.

=71. Method of Lawes.=—In a late method of sampling proposed by Sir J. B. Lawes[55] a steel frame ten by twelve inches, and nine inches deep open at top and bottom is driven into the earth until its upper edge is level with the surface of the soil. All above-ground vegetation is then cut off as closely as possible with scissors. The soil within the frame is then removed exactly to the depth of the frame, and immediately weighed. It is then partially dried, and mechanically separated by a series of sieves, all visible vegetable matter being at the same time picked out. The stones and roots and the remaining soil are thus separated, and the determinations of dry matter, nitrogen, etc., are made in the separated soil after being finely powdered. The loss of water at each stage of preparation and on drying the samples as analyzed is also carefully determined. This method, which requires the soil to be taken to an arbitrary depth of nine inches, could not be used when samples of strictly arable soil are to be taken.

=72. In taking= a sample by the French commission[56] method it is necessary to remove from the surface, the living and dead vegetation which covers the soil. With a spade a square hole is then dug to the depth of about 500 millimeters; in other words, to a depth considerably exceeding that of the arable layer. Afterwards on each of the four sides of the hole there is removed by the spade, a prismatic layer of the arable portion of a thickness equal to its depth. The samples thus obtained are united together and carefully mixed for the purpose of forming a sample for analysis. If there are large stones they are removed by hand and their proportion by weight determined.

In all cases it would prove useful to take a sample of the subsoil which is far from playing a secondary rôle. The rootlets bury themselves deeply in it and seek there a part of their nourishment. The subsoil, therefore, furnishes an important addition to the alimentation of the plants. For taking a sample of the subsoil a ditch is dug of sufficient depth, say one meter, and the arable soil carefully removed from the top portion. Afterwards pieces are taken from the four sides of the hole at variable depths, which should always be indicated, and which should extend in general, from six to eight-tenths of a meter below the arable soil since it is demonstrated that the roots of nearly all plants go at least to this depth. The analysis of the subsoil, however, is less important than that of the soil, properly so-called, because the agronomist does not act directly upon it and takes no thought of modifying it and enriching it as he does the layer of arable soil. But the composition of the subsoil is a source of information capable of explaining certain cultural results and capable sometimes, of leading to the correct way of improving the soil, as in cases where the subsoil can be advantageously mixed with the superficial layer.

=73. Wolff=[57] suggests that a hole thirty centimeters square be dug perpendicularly and a section from one of the sides taken for the sample. To the depth of thirty centimeters the sample shall be taken as soil and to the additional depth of thirty centimeters as subsoil. The thickness of the section taken may vary according to the quantity of the sample desired. For analytical purposes, five kilograms will usually be sufficient. When culture experiments are also contemplated a larger quantity will be required.

=74. Method of Wahnschaffe.=—The method of sampling advised by Wahnschaffe[58] is but little different from that of Wolff already mentioned.

A square sample hole is dug with a spade having its sides perpendicular to the horizon. The soil which is removed is thrown on a cloth and carefully mixed. From the whole mass a convenient amount is next removed care being taken not to include any roots. In a similar manner it is directed to proceed for the sample of subsoil. At first the subsoil should be removed to a depth of two to three decimeters. The number and depth of subsequent samples will depend chiefly upon the character of the soil. Where samples are taken to the depth of two meters the use of a post-hole auger is recommended.

The samples taken should not be too small. In general from two to three kilograms should remain after all preliminary sampling is finished.

=75. Method of König.=—The directions given by König[59] for taking soil samples are almost identical with those prescribed by Wahnschaffe and do not require any further illustration.

=76. Special Instruments Employed in Taking Samples.=—In general a sharp spade or post-hole auger is quite sufficient for all ordinary sampling but for certain special purposes other apparatus may be used.

The instrument which is used by King[60] consists of a thin metal tube of a size and length suited to the special object in view, provided with a point which enables it to cut a core of soil smaller than the internal bore of the tube and at the same time make a hole in the ground larger than its outside diameter. Its construction is shown in figure 11, in which A B represent a soil tube intended to take samples down to a depth of four feet. A′ is a cross-section of the cutting end of the tube, which is made by soldering a heavy tin collar, about three inches wide, to the outside of a large tube allowing its lower end to project about one-half an inch. Into this collar a second one is soldered with one edge projecting about one-quarter of an inch and the other abutting directly against the end of the soil tube. Still inside of this collar is a third about one-half an inch wide which projects beyond the second and forms the cutting edge of the instrument.

FIGURE 11.
]

The construction of the head of the tube is shown at B′. It is formed by turning a flange on the upper end of the tube and then wrapping it closely with thick wire for a distance of about three inches, the wire being securely fixed by soldering. The soil tube should be of as light weight as possible not to buckle when being forced into the ground, and the cutting edge thin. The brass tubing used by gas fitters in covering their pipes has been found very satisfactory for ordinary sampling. With a one inch soil tube four feet long it is possible to get a clear continuous sample of soil to that depth by simply forcing the tube into the ground with the hand and withdrawing it, or the sample may be taken in sections of any intermediate length. Later in the season when the soil becomes dryer it is necessary to use a heavy wooden mallet to force the tube, and this should be done with light blows.

The closeness with which it is possible to duplicate the samples in weight by this method will be seen below, where from each of four localities three samples were taken from the surface to a depth of four feet.

SHOWING VARIATIONS IN THE DRY WEIGHT OF TRIPLICATE SAMPLES OF SOIL.

─────────────────────────┬──────────┬──────────┬──────────
│ A. │ B. │ C.
─────────────────────────┼──────────┼──────────┼──────────
I. Surface to four feet│716.6 gms.│715.5 gms.│710.3 gms.
II. Surface to four feet│715.4 gms.│687.1 gms.│731.2 gms.
III. Surface to four feet│654.0 gms.│688.3 gms.│709.0 gms.
IV. Surface to four feet│714.0 gms.│687.8 gms.│719.3 gms.

These four series of samples were taken at the four corners of a square twelve feet on a side and serve to show how much samples may vary in that distance. The large difference shown in III, A is due to the fact that the soil tube penetrated a hole left by the decay of a rather large root as shown by the bark in the sample.

=77. Auger for Taking Samples.=—It has already been said that the ordinary auger used for boring fence post-holes may be used to advantage in taking soil samples. Large wood augers can also be used to advantage for the same purpose. For special purposes, however, other forms of augers may be used.

Norwacki and Borchardt[61] have described a new auger for taking samples of soil for analytical purposes.

FIGURE 12.
]

In figure 12, A, B and C show the general exterior and interior form of the instrument. The handle is hollow and made of iron gas pipe covered with leather. On the inside of this, in the middle, is fixed a wooden plug a, which leaves two compartments, one in each end for holding the brass plug bb,’ and the wicker lubricating wad cc.’ The stem of the auger a, is heavy and made of eight-sided steel and the under end is strengthened with a heavy casting fitting into the auger guide g g. The end of the auger I I′ is triangular and hardened. The auger guide g g, is made out of a single piece of drawn steel tubing. Above it is strengthened by a ring-shaped piece of iron or copper and its lower end is furnished with saw teeth as shown in K and is hardened. The fixing key e, is bent in the form of a hook and can be passed through the two holes o o, of the auger stem and through the one hole o′ in the strengthened part of the auger guide. It permits the auger guide to be fixed upon the auger stem in two different positions, higher and lower. On one end it is cut squarely across and on the other provided with a conical hole drilled into it. It fits on the one hand exactly in the auger guide and on the other loosely plays in the cavity of the handle at b, designed to hold it when not in use. The cap d′ is made of heavy sheet brass and is fastened upon the end of the handle at c c′ after the manner of a bayonet. The wicker cartridge is made of rolled and sewed wicker-work. At the upper end it is provided with a metallic button and before use it is saturated with paraffin oil. It fits on the one side firmly in the auger guide and on the other in the cavity, of the handle c where it is kept when not in use. The union h is made of a brass tube which below is closed with a piece of solid brass upon the inside of which a hole is bored. In this hole rests the end of the auger stem when the union is placed firmly upon the auger guide.

The auger is placed together as is shown in A B, the union h is taken off and it is driven with gentle blows, turning it back and forth, to the proper depth into the soil. After the key is loosened the auger is lifted high enough so that the second hole appears and then it is fixed in position by the key. Then the boring is continued, turning the auger to the right, by which the auger, eating its way with its saw teeth, presses deeper into the ground and withdraws the material for analysis. After the auger guide has been filled through any desired length, say five to ten centimeters with the sample of soil, the whole auger is drawn out of the soil, the key removed, the auger stem withdrawn from the auger guide, the apparatus opened by turning the bayonet fastening of the stopper on the handle, the brass plug placed in the end and then with the smooth part forward, from above, it is allowed to fall into the auger guide until it reaches the soil. The auger stem is then put back, the point of it fitting into the hole of the plug and the sample of soil shoved out of the auger guide. The auger guide is again fixed on the auger stem by the key and then the apparatus is ready for a second operation. When the borings cease the wicker cartridge is drawn out of the handle and shoved, the soft end forward, from above, into the auger guide and the brass plug after it and pushed through with the auger stem. By this process the wicker cartridge gives up a sufficient amount of paraffin oil to completely grease the inside of the auger guide and to protect it from rust. After use the instrument should be cleaned on the outside by means of a cloth, the plug and wicker wad replaced in their proper positions, the cap fixed on the handle and the union on the point of the instrument.

The length of the whole apparatus may reach one meter or more; the internal diameter sixteen millimeters. The apparatus weighs with a length of one meter, together with all its belongings, about two kilograms. For the investigation of peat and muck soils as well as sand, instead of the steel auger guide one of brass or copper can be used. For this purpose the length of the apparatus may reach three to four meters.

In comparison with other apparatus which are used for taking samples, it appears without doubt that with the one just described a better and less mixed portion of the soil can be obtained at great depths. The apparatus is said to have many advantages over a similar one known as Fraenkel’s, and is much more easy to clean. The advantages of the apparatus are said to be the following: The farmer with this piece of apparatus in a short time can go over his whole farm taking samples to the depth of ninety centimeters since a single boring does not take more than one minute. Geologists and others interested in the soil at greater depths can use an apparatus three to four meters in length and obtain unmixed samples from these lower depths. These are also interesting from a bacteriologic point of view. The entire apparatus is especially valuable for the investigation of the lower parts of peat and muck soils. The apparatus has been tried in the collection of samples for the laboratory of the Department of Agriculture and is too complicated to be recommended for ordinary use. When however samples are to be taken at great depths as in peat soils it is highly satisfactory.

=78. Soil Sampling= depends for its success more on the judgment and knowledge of the collector than on the method employed and the apparatus used. One skilled in the art and having correct knowledge of the purpose of the work will be able to get a fair sample with a splinter or a jack-knife while another with the most elaborate outfit might fail entirely in collecting anything of representative value.

There are some special kinds of soil sampling, however, which cannot be left to the method of the individual and it is believed that with the descriptions given above nearly all purposes for which samples are desired may be served.

For the study of nitrifying organisms, however, special precautions are required and these will be noted in a more appropriate place.

In taking samples for moisture determinations the method of Whitney is recommended as the best. For the general physical and chemical analytical work the standard methods are all essentially the same. The principles laid down by Hilgard will be found a sufficient guide in most cases.

TREATMENT OF SAMPLE IN THE LABORATORY.

=79. The Sample=, or mixed sample, taken by one of the methods above described, is placed on a hard smooth board, broken up by gentle pressure into as fine particles as possible and all pieces of stone and gravel carefully removed and weighed; all roots, particles of vegetable matter, worms, etc., are also to be weighed and thrown out. This can be done very well by using a sieve of from one to two millimeter mesh. Care should be taken that the soil be made to pass through, which can be accomplished by subjecting the lumps to renewed pressure with a rubber-tipped pestle. In the above operation the soil should be dry enough to prevent sticking. The relative weights of the pebbles, roots, etc., and the soil should be determined.

=80. Order of Preliminary Examination.=—Hilgard[62] commences the examination of a soil sample by washing about ten grams of it into a beaker with a water current of definite velocity, stirring meanwhile actively the part carried into the vessel. The residue not carried by the current is examined macro- and microscopically to determine the minerals which may be present, and the condition in which the fragments exist—whether sharp or rounded edges, etc.

This examination will give some general idea of the parent rocks from which the sample has been derived and of the distance the particles have been transported. Next follows the hand test, _viz._, rubbing the soil between the thumb and fingers first in the dry state and afterwards kneading it with water and observing its plasticity. Following this should come a test of the relations of the sample to water, _viz._, its capacity for absorbing and retaining moisture. Finally the separation of the soil into particles of definite hydraulic value and a chemical examination of the different classes of soil concludes the analytical work.

=81. Air Drying.=—The sifted soil should be thoroughly mixed and about one kilogram spread on paper and left for several days exposed in a room with free circulation of air and without artificial heat. The part of the sample to be used for the determination of nitrates should be dried more quickly as described in another place. The sample is then placed in a clean, dry glass bottle, corked, sealed, and labeled. The label or note book should indicate the locality where the sample was taken, the kind of soil, the number of places sampled, and other information necessary to proper description and identification.

=82. Caldwell=[63] directs that having taken the sample to the laboratory, the stones and larger pebbles should be separated from the finer parts by the hand, or by sifting with a very coarse sieve, and examined with reference to their mineralogical character, weight and size, making note, in this last respect, of the number that are as large as the fist or larger, the number as large as an egg, a walnut, hazel-nut, and pea, or give the percentage of each by weight.

Pulverize the air-dried soil in a mortar with a wooden pestle, and separate the fine earth by a sieve with meshes three millimeters wide; this sieve should have a tightly fitting cover of sheepskin stretched over a loop, and it should be covered in the same manner underneath, so that no dust can escape during the process of sifting.

Wash the pebbles and vegetable fibers remaining on the sieve with water, dry and weigh the residue; the water with which this gravel was washed should be evaporated to dryness at a temperature not exceeding 50° towards the close of the evaporation, and the residue mixed with what passed through the dry sieve.

The sifted fine earth is reserved for all the processes hereinafter described, and is kept in well-stoppered bottles, marked air-dried fine earth. The sieve mentioned above is too coarse for the more modern methods of analysis.

=83. Wolff=[64] directs that the air-dried earth (in summer dried in thin layers at room temperature, in winter in ovens at 30° to 50°) be freed from all stones, the latter washed, dried, and weighed. The soil is next passed through a three millimeter mesh sieve, the residual pebbles and fiber washed, dried and weighed. The fine earth passing the sieve is used for all subsequent examinations. It is air-dried at moderate temperatures and preserved in stoppered glass vessels.

=84. The French=[65] commission calls especial attention to the method of subsampling, and prescribes that the sample of earth which has been taken in the manner indicated, and of which the weight should be greater as the material is less homogeneous should not be analyzed as a whole. It should be divided into two parts. The first includes the finer particles constituting the earth, properly so-called, with the elements which alone enter into play in vegetable nutrition and on which it is necessary to carry out the analysis. The second embraces the coarser particles to which only a superficial examination should be given and which may have a certain importance from a physical point of view but which cannot take any part from a chemical point of view, in the nutrition of plants. It is, however, useful to examine its mineralogical constitution and to look for the useful elements such as lime, potash, etc., which it may be able to furnish to the earth, and in proportion as it is decomposed, finer particles which may be useful in plant nutrition.

How are we to distinguish between the fine and coarse elements? All grades of fineness are observed in the soil, from the particles of hydrated silica so small that with the largest magnifying power of the microscope it is scarcely possible to distinguish them, up to grains of sand which are of palpable size and visible to the naked eye, and extending to pebbles of varying sizes. All intermediate stages are found between these and if it should be asked what is the precise limit at which it is necessary to stop in distinguishing the fine from the coarse elements of the soil, the answer is that this can only be determined by a common understanding among analysts. In general, it may be said, that the mark of distinction should be the separation which can be secured with a sieve having ten meshes per centimeter.

=85. Loose Soils.=—Having agreed upon a sieve of the above size, the process of separation in loose soils is as follows: The earth is exposed to the air and when the touch shows that it is sufficiently dry the conglomerated particles should be simply divided without breaking the rocky material which exists in a state of undivided fragments. There are some special precautions to be taken. Rubbing in a mortar must be forbidden since it reduces the earth to particles which are unnatural in size, by securing the breaking up of the fragments consisting of the débris of rocks. When it is possible the earth should be rubbed simply in the hand and after having separated that which passes the sieve, the large particles which have not passed should be again rubbed with the hand, until all the particles which can be loosened by this simple treatment have passed the sieve. The separation should be as complete as possible in order that a sample of the particles passing the sieve should represent as nearly as possible, a correct sample of the fine particles of the soil.

In regard to the pebbles, they should be washed with water upon the sieve in order to carry through the last of the particles of earth adhering to them. They are then dried and their weight taken. The fine part of the earth is also weighed. On an aliquot part, say 100 grams, the moisture is determined and then by simple calculation the whole sample of the air-dry soil can be calculated to the dry state. The sample is then placed in a glass flask.

The pebbles are examined with a view of determining their mineralogical constitution; as for instance, on being touched with a little hydrochloric acid it can be determined whether or not they are carbonate of lime. The nature of the rock from which they have been derived is often to be determined by a simple inspection.

=86. Compact Soils.=—If the soils are not sufficiently loose to be treated as before described, it is necessary to have recourse to other means of division, which should not, however, be sufficiently energetic to reduce the rocky elements to fine particles. For this purpose the earth may be broken by means of a wooden mallet, striking it lightly and separating the fine elements from time to time by sifting. A wooden roller may also be used with a little pressure, for breaking up the particles or a roller made out of a large glass bottle. These methods will permit of a sufficiently fine division of the soil without breaking up any of the pebbles. Sometimes, however, a soil can not be broken up by such treatment. It is then necessary to have recourse to the following process: The soil is thoroughly moistened and afterwards rubbed up with water. The paste which is thus formed, is poured upon the sieve and washed with a stream of water until all the fine particles are removed. The wash water and the fine particles are left standing until the silt is thoroughly deposited when the supernatant water is poured off and the deposited moist earth is transferred into a large dish and dried on a sand or water-bath. In this way a firm paste is formed which can be worked up with the hand until rendered homogeneous and afterwards an aliquot portion be taken to determine moisture.

=87. Method of Peligot.=—The method recommended by Peligot[66] for the preparatory treatment of the sample is essentially that already described. The sample is at first dried in the air and then in an oven at 120°. When dry and friable 100 grams are placed in a mortar and rubbed with a wooden pestle. It is then passed through a sieve of ten meshes per centimeter. The largest particles which remain in the sieve should have about the dimensions of a pin’s head. The stones are separated by hand. They should be shaken with water in order to detach any pulverulent particles adhering thereto. The turbid water resulting from this treatment is added to that which is used in separating the sand from the impalpable part of the soil.

=88. Wahnschaffe= prescribes[67] in the further preparation of the sample for analysis that the coarse pieces up to the size of a walnut be separated in the field where the sample is taken and their relative weight and mineralogical character determined. The soil sample is then to be placed in linen or strong paper bags and carefully labelled. In order to avoid any danger of loss of label the description or number of the sample should be put on the cloth or paper directly.

The sample when brought to the laboratory should be spread out to dry, in a room free of dust. In the winter the room should be heated to the usual temperature. The air drying should continue until there is no sensible loss of weight. The samples then are to be placed in dry, glass-stoppered glass bottles where they are kept until ready for examination. This method of keeping the samples avoids contact with ammonia or acid fumes with which a laboratory is often contaminated.

=89. The Swedish= chemists[68] direct that samples which are to be used for chemical examination in the manner described below, are most conveniently brought to such a condition of looseness and humidity that the soil feels moist when pressed between the fingers without, however, sticking to the skin. To prepare the sample in this manner, spread it in a large porcelain dish or on a glass plate in a place where it is not reached by the laboratory atmosphere; stir it frequently till it assumes the mentioned humidity (if the sample when sent is too dry, moisten it with distilled water till its condition is as indicated); then pulverize carefully between the fingers and finally sift through a sieve with five millimeter holes. In this way free the sample from stones, undecayed roots and similar parts of plants, pieces of wood, and other matter strange to the soil, which remain on the sieve; mix the sample carefully and put it into a glass bottle provided with a stopper well ground in; keep it in a cool place. Samples prepared in this way will usually contain 20–30 per cent moisture; boggy soils 60–80 per cent and peat soils 50 per cent.

=90. Petermann=[69] follows the method below in preparing samples of soil for analysis.

The soil is gently broken up by a soft pestle and all débris if of organic nature, cut fine with scissors. About 2500 grams of this soil are passed through a one millimeter mesh sieve. The organic débris is removed by forceps, washed free of adhering earth dried at 120° and weighed. The nature of the organic débris should be noted as carefully as possible.

The pebbles and mineral débris not passing the sieve are worked in a large quantity of water by decantation. They are also dried at 120° and weighed. This débris is examined mineralogically and thus some idea of the origin of the soil obtained.

=91. The= various methods for the preliminary treatment as practiced by the best authorities have been somewhat fully set forth in the foregoing résumé. The common object of all these procedures is to get the soil into a proper shape for further physical and chemical examination and to determine the comparative weights of foreign bodies contained therein.

The essential conditions to be observed are the proper sifting of the material and avoidance of mechanical communition of the solid particles too large to pass the meshes of the sieve. If possible the material should be passed through a sieve of one millimeter mesh. In cases where this is impracticable a larger mesh may be used, but as small as will secure the necessary separation. Before final chemical analysis a half millimeter mesh sieve should be employed if the soil be of a nature which will permit its use. Over-heating of the sample should be avoided. Rapid drying is advisable when the samples are to be examined for nitrates.

The method recommended by the French commissions seems well adapted to the general treatment of samples, but the analyst must be guided by circumstances in any particular soil.

AUTHORITIES CITED IN PART SECOND.

Footnote 39:

Bulletin 38, pp. 61–2.

Footnote 40:

Ms. communication to author.

Footnote 41:

Bulletin No. 10.

Footnote 42:

Landwirtschaftliche Versuchs-Stationen, Band 38, Ss. 309 et seq.

Footnote 43:

Annales de la Science Agronomique, Tome 1, Part 2, p. 240.

Footnote 44:

Agricultural Chemical Analysis, p. 166.

Footnote 45:

Zeitschrift für analytische Chemie, Band 3, S. 87.

Footnote 46:

Anleitung zur Wissenschaftlichen Bodenuntersuchung, S. 17.

Footnote 47:

Traité de Chimie Analytique, p. 149.

Footnote 48:

Bulletin 35, p. 108.

Footnote 49:

Op. cit.

Footnote 50:

Bulletin 10, p. 33.

Footnote 51:

Analyse des Matières Agricoles, p. 131.

Footnote 52:

Bulletin 38, p. 200.

Footnote 53:

This in some instances would include a part of the subsoil.

Footnote 54:

All soils do not become friable on drying.

Footnote 55:

Journal of the Royal Agricultural Society, (2), Vol. 25, p. 12.

Footnote 56:

Annales de la Science Agronomique, Tome 1, Part Second, pp. 240 et
seq. The personnel of the commission is as follows: MM. Risler,
Grandeau, Joulie, Schloesing, and Müntz.

Footnote 57:

Vid. 7.

Footnote 58:

Anleitung zur Wissenschaftlichen Bodenuntersuchung, S. 17.

Footnote 59:

Untersuchung Landwirtschaftlich und Gewerblich Wichtiger Stoffe, S. 5.

Footnote 60:

Seventh Annual Report of the Wisconsin Agricultural Experiment
Station, p. 161.

Footnote 61:

Deutsche Landwirtschaftliche Presse, Band 19, No. 35, Ss. 383–4.

Footnote 62:

Journal American Chemical Society, Vol. 16, p. 36.

Footnote 63:

Agricultural Chemical Analysis, p. 168.

Footnote 64:

Vid. 7.

Footnote 65:

Vid. 16.

Footnote 66:

Vid. 9.

Footnote 67:

Vid. 8, p. 19.

Footnote 68:

Methods of Analysis of Soils, Fertilizers, etc., adopted by the
Swedish Agricultural Chemists, translated for the author by F. W.
Woll.

Footnote 69:

L’Analyse du Sol, p. 14.

PART THIRD.

PHYSICAL PROPERTIES OF SOILS.

=92. The Soil as a Mass.=—The soil constituted as indicated in the preceding pages, is now brought to the analyst for investigation. The properties with which he first becomes acquainted are those which impress his senses as mass characteristics. There is a perception of color, consistence, weight and other features which the soil possesses as a whole. The several constituents of the soil must first be considered as molecular and mole aggregates. In other words, the soil in its natural state is a mechanical mixture of particles which must first be considered as a whole. The physical properties of the soil, therefore, should engage the attention of the analyst before he proceeds to the investigation of the properties of its several constituents as classified by the relative size or hydraulic value of the particles of which they are composed, or to a chemical determination of the compounds or elements therein contained.

DETERMINATION OF PHYSICAL PROPERTIES.

=93. Color.=—The color of a soil depends chiefly upon the proportion of organic matter and iron compounds which it contains and the state of subdivision of its particles. When a soil contains a large amount of organic matter, especially when this organic matter is in an advanced state of decay, it assumes more or less a black color when moist. This black color is to be distinguished from the black alkali tint which is produced by the action of carbonate of soda on organic matter. The naturally black color of a soil containing a large amount of organic matter depends, however, either upon the action of mineral matters upon this organic matter, as in the case of the black alkali mentioned, or upon the blackish color of carbon resulting from the slow combustion of the organic matter during the period of decay.

The presence of a large amount of ferric oxid in soil gives the well-known red color so well-marked in the soils of southwestern Kentucky and other portions of the United States. The preponderance of sand in a soil tends to produce a light yellow or whitish tint, while certain kinds of clay have a bluish tint probably due to the presence of ferrous salts. The influence of the color of the soil upon the color of the vegetation is also well-marked, the black soils as a rule producing a much deeper green tint of foliage than the light colored soils. This effect should not be attributed to color alone for as a matter of fact highly colored soils are usually very close and very retentive of moisture, which is one reason, probably, for their not being more highly oxidized. Such soils will produce a more vigorous and ranker growth of vegetation, but it is the texture of the soil and the more moist condition which it maintains, rather than the color, which produce the deeper green tint of foliage.

The color of a soil is also used as an index of its fertility, the black and red soils being usually the most fertile.

It may be well to add here the probable reason as given by Whitney for this, _viz._, that the deeper color shows that the oxids of iron and the organic compounds have less oxygen and indicate that the soils are quite retentive of moisture and rather tend to the exclusion of air, so that part of the oxygen of the iron compounds and of the organic matters has been used up in the oxidation processes within the soil. It is known, for example, that wood oxidizes much more rapidly around a rusty nail than where it is simply exposed to the air, the iron oxid acting as a carrier between the oxygen of the air and the organic matter. In a sandy soil, on the contrary, where there is usually less moisture and much freer circulation of air, the iron compounds have more oxygen and usually have a light yellow color. If this sand is heated, however, with the exclusion of air, and especially in the presence of organic matters, part of this oxygen will be given off and there will be the same red color as in the heavier clay soils. It is frequently noticed, also, in compact clays that where air gains access through cracks or root-holes, the color is altogether modified.

=94. Determination of Color.=—There is no process which will give experimentally and accurately the color of a soil sample. The changes which the color of a soil undergoes in passing from a saturated to an anhydrous state are well-marked. The analyst will have to be content with giving as nearly as possible a description of the color of the sample when taken and the changes which it undergoes in air drying or on heating in a bath to 100°–110°, or in heating to redness with or without exclusion of the air. These changes in color will give some indication of the character of the organic and mineral matters present.

=95. Odoriferous Matters in Soil.=—It is known that the soil emits a peculiar odor which is not disagreeable except when it has been recently wet, for instance, after a short rain. Several attempts have been made to discover the nature of this odor. These researches have established the fact that the essential principle of this odor resides in an organic compound of a neutral nature of the aromatic family and which is carried by the vapor of water after the manner of a body possessing a feeble tension. The odor is penetrating, almost piquant, and analogous to that of camphorated and quite distinct from other known substances. In regard to the quantity of this substance, it is extremely minute and can be regarded as being only a few millionths of a per cent.

According to Berthelot and André[70] this new principle is neither an acid nor an alkali nor even a normal aldehyd. It is, in a concentrated aqueous solution, precipitable by potassium carbonate with the production of a resinous substance. Heated with potash it develops a sharp odor similar to the aldehyde resin. It does not reduce the ammoniacal nitrate of silver. Treated with potash and iodin it gives an abundant formation of iodoform, which, however, is a property common to a great number of substances. For the qualitative and quantitative estimation of the odoriferous matter the following process is employed:

About three kilograms of the soil are mixed with sand containing a small amount of carbonate of lime and some humic substance; after having freed it from all organic débris which is visible, it is placed in a glass alembic. The soil should contain from ten to twelve per cent of water at least. The alembic is placed in a sand bath and is kept at 60° for several hours. The water evaporated is condensed until about seventy-five cubic centimeters are distilled over. This distilled water is again rectified so as to obtain in all about twenty cubic centimeters. The odoriferous matter appears to be nearly all contained in this twenty cubic centimeters. The liquid thus obtained shows an alkaline reaction; it contains some ammonia and reduces ammoniacal silver nitrate. This last reaction is due to some pyridic alkali or analogue thereof, and is cause for it to be distilled anew with a trace of sulfuric acid which gives a neutral liquor deprived of all reducing action but which preserves the odor peculiar to the soil. The twenty cubic centimeters obtained as before are subjected to two additional distillations and in the final one only one cubic centimeter of liquid is distilled over.