Manual of general agriculture

Introduction

The experiments in this manual represent actual work done by the author's classes during several years teaching of the subject of general agriculture in High Schools in Northern and Southern California. There is sufficient material to occupy the laboratory time of a High School class at least four periods a week for one year. Not all the exercises are suitable for any one locality, but nearly all can be used any place. The manual is not intended to displace any text.

A satisfactory plan for conducting a course in general agriculture is to have each student own a manual and have the school furnish the references to accompany it. As the recitations do not occur every day, one book for three students will be found sufficient. Usually the local library will supply a portion of the books needed. A list of references will be found in the back of this manual.

A note book containing a record of each exercise performed should be kept by the student. The following form is suggested :

Number and statement of exercise.

Exercise.

Result.

Conclusion

It is unnecessary for the student to copy materials. At the beginning of nearly all the exercises will be found a list of materials needed, but special attention is called to the following, the materials for which cannot be obtained at once : 46, 56, 57, 58, 59, 62, 63, 64, 67, 68, 69.

The author wishes to express his thanks for council and material contributed by Principal E. L. Mitchel, Professors W. T. Clarke, R. H. Loughridge, A. D. MacGillivray, H. H. Whetzel, C. S. Wilson, E. G. Montgomery, Messrs. A. R. Tyler, Geo. C. Roeding and Miss May Kimble. The cuts under Budding and Grafting were taken from Farmers' Bulletin No. 157. With slight changes, exercises 31, 32, 33, 34, 45, 46, 47 and 50 are by Prof. F. E. Edwards.

PART I. PHYSICAL PROPERTIES OF SOILS. Page

1. How Soils are Formed 7

2. Taking Soil Samples 7

3. Microscopical Examination of Soil Particles. ... 8

4. Determination of Total Moisture in the Soil ... 9

5. Capillarity 10

6. Effect of Drainage on Soil Temperature 11

7. Effect of Color on Soil Temperature 12

8. Effect of Evaporation on Soil Temperature 13

9. Per Cent, of Air in Soils 14

30. Separation of Sand, Silt and Clay in Soils 14

11. Water Holding Capacity of Soils 15

12. Effect of Humus on Water Holding Capacity of

13. Effect of Mulches and Cultivation on Evapora-

tion from the Soil 16

14. Effect of Vegetable Matter on the Capillary Rise

of Water 17

15. Effect of a Moist Atmosphere on Dry Soils.... 17

16. Effect of Lime on Soils 18

17. One Effect of Humus, of Sand and of Lime, on a

Clay Soil 19

18. Determination of the Specific Gravity of Soils. . 19

19. Determination of the Apparent Specific Gravity

of Soils 20

Part II. Chemical Properties Of Soils. Soil Analysis

20. Acids, Alkalis and Salts 21

21. Preparation of Potash 22

22. Preparation of Crude Phosphoric Acid 22

23. Alkali Soils 23

24. Gypsum Treatment for Black Alkali 25

25. Acid Soils and How to Correct Them 25

26. Directions for Obtaining Soil Samples 27

CONTENTS. 5

Page.

27. Determination of Nitrogen 28

28. Determination of Phosphoric Acid 29

29. Determination of Lime 30

30. Determination of Alkali 31

Part III. Chemistry Of Plants

31. Moisture in the Plant 33

32. Composition of Dry Matter of Plants 33

33. Composition of Plant Ash 34

34. Nitrogen in Plants 36

35. Plant Nutrition 36

36. Nitrogen in Nodules. 39

37. Tests for Principal Classes of Plant Compounds. . 40

38. Occurrence and Extracting of Starch 41

39. Inversion of Cane Sugar 42

40. Preparation of Glucose 42

41. Essential Oil From Plants 43

42. Extraction of Proteids 43

43. Extraction and Decomposition of Chlorophyll. . 44

44. Determination of Oil in Flaxseed 44

45. Absorption of Manure by the Soil 45

46. Fertilizer Field Tests 45

Part IV. Agricultural Botany And Plant Propagation

47. Conditions Necessary for Germination... 47

48. Purity of Seed and Germination Test 17

49. Plump and Shrunken Seeds 49

50. Depth of Germination 49

51. Osmosis 50

52. The Work of Leaves 51

53. Study of the Characters of Barley 52

54. Outline for Describing Grasses 58

55. Identification of Clover and Grass Seeds 59

56. Cuttings and Their Use in Propagation 60

57. Establishing a Deciduous Orchard 62

58. Grafting 65

59. Budding 69

6 CONTENTS.

Page

60. Laying out an Orchard 72

61. How to Plant a Tree 73

62. Propagation of the Grape 74

63. Propagation of the Orange 77

64. Pruning Fruit Trees, Vines and Bushes 78

65. Structure and Nature of Fungi 81

66. Structure and Nature of Bacteria 81

Part V. Enemies Of Crops

67. Apple Scab 83

68. Fire Blight or Pear Blight 85

69. The Mouth-parts of Insects 88

Part VI. Testing Milk And Its Products

70. Experiments With Milk 94

71. Analysis of Milk 95

72. Test for Mineral Salts in the Ash of Milk 97

73. Calibration or Correction of Glassware 98

74. Determination of the Specific Gravity or Strength

of Sulphuric Acid 99

75. The Babcock Test of Milk 100

76. The Babcock Test of Cream 103

77. The Babcock Test of Skim Milk 104

78. The Lactometer and Its Application 105

79. Testing the Acidity or Sourness of Milk and

Cream 107

80. Calculation of the Percentage of Milk Solids 107

81. Test for Physical Adulteration of Milk 108

82. Test for Chemical Adulteration of Milk 109

83. Determination of Moisture in Butter 110

84. Determination of Salt in Butter 112

85. Determination of Per Cent. Fat in Ice-cream. . .112

86. Standardization of Milk and of Cream 113

Part I. Physical Properties Of Soils

1. HOW SOILS ARE FORMED. (FIELD EXERCISE.)

(a) Work of Atmosphere. — 1. Note any rocks worn away by the friction of wind or sand through the action of the wind. Note any rocks kept exposed to other atmospheric agencies through the action of the wind; note any wind-bloAvn soil; any wind-blown water.

2. Note any evidences of chemical action; oxidation; action of carbon dioxid; "rotten rock." Make a drawing showing successive stages of disintegration from solid rock to soil.

(b) Work of Water. — 1. Note any evidences of its solvent power. Fill a small bottle with clear water from a spring or brook and when you return to the laboratory evaporate a few drops of it on a piece of glass or in a test tube, and see if there is any residue ; explain.

2. Disintegrating Power of Water. — Note evidences of the washing out of loose material, and of cutting power of the water; of the abrasion caused by gravel, pebbles and stones.

3. Transporting Power of Water. — Why is one stream clear, and another muddy? Note any sand or soil dropped by water.

4. Note evidences of assorting power of water. Draw a section of the bank of a stream, showing stratification.

5. Note evidences of under-ground streams, of landslides, and describe and explain.

2. TAKING SOIL SAMPLES. (FIELD EXERCISE.)

Materials: Spade, paid, two one quart fruit jars, or two bottles with corks.

Select a spot for sampling and remove any leaves and twigs from the surface. Dig into the cleared space a V-shaped hole, with one side of the V perpendicular. On the perpendicular side measure the depth to the change in color, which indicates the division between surface soil and subsoil. With the spade shave thin slices from the perpendicular side to the depth of the surface soil, collecting the soil in a pail until you have about a quart. If there is no marked line between soil and subsoil, sample to a depth of one foot.

Without filling up the hole go to at least one other part of the field and in a similar manner obtain another sample, place in the pail with the first sample and mix thoroughly. Save about a quart as a sample of the field, and keep air-tight to prevent loss by evaporation.

Continue digging to the depth of about one foot below the surface soil and collect a sample of subsoil by shaving thin slices as before and placing in the pail. Fill up the hole. Return to the original hole and obtain a sample of subsoil, mix the two subsoils and keep air-tight as was done with the surface soil.

3. MICROSCOPICAL EXAMINATION OF SOIL PARTICLES.

Materials: Compound microscope, sand, loam or silt, clay soil, or clay.

Place a few grains of sand on a glass slide and examine with low power of a microscope.

Make drawings of several of the particles and describe them, with reference to color; shape (angular, rounded, or irregular) ; simple or compound (joined together) ; coarse, medium or fine.

Mix loam or silt with a little water and examine a drop, using medium power. Draw and describe as above.

Mix clay soil with water and examine a drop of the slightly muddy water using the high power. Notice that the soil particles are really minute rocks and humus. Find dark particles of humus. Find flocculated particles of clay, i.e. a number of particles united to form a compound particle. Draw and describe. Keeping a clay soil in good condition is largely a matter of keeping the particles thus flocculated or united into small crumbs.

MANUAL OF GENERAL AGRICULTURE.

4. DETERMINATION OF TOTAL MOISTURE IN THE SOIL.

Materials: Pour tin pans, sheet iron drying oven*, samples collected in Exercise 2.

Number, mark with your initials and accurately weigh four pans. Record weights in your note book. Run all your experiments in duplicate for the sake of greater accuracy.

Place in pans 1. and 2, 50 grams of surface soil, and in pans 3 and 4, 50 grams of subsoil. Put them in the drying oven for at least five hours at a temperature of 100 to 110 degrees centigrade. Cool to room temperature and weigh at once. The loss in weight represents the total moisture content of the soil.

Tabulate the results as follows :

TOTAL MOISTURE IN SOILS.

Kind of Soil

Pan No.

Wt. of Pan

Wt. of Soil

Wt. of Dry Soil

Loss of Weight

Per Cent Moisture

Avg.

Kind of Soil

Avg.

Questions: 1. What were the weather conditions at the time of taking the samples? 2. Approximately, when was the last heavy rain? 3. Does the soil or subsoil have the most moisture? Why?

*A better oven is of copper set on a strong iron frame. It should be about 10 in. high, 10 in. deep, and 12 in. wide. The oven is provided with a centigrade thermometer and has a vent for the escape of moisture. It costs approximately eight dollars. As it is needed throughout the entire course, it is advisable to obtain one.

10 MANUAL OF GENEEAL AGKICULTUEE.

5. CAPILLARITY.

mg dish, alcohol or kerosene. Soil and subsoil collected m Exercise 2 For (d), 4 glass tubes at least 4 ft. long and of any diameter up to one inch, the larger the bett^er, pan, sand, sandy soil, loam, clay, small cloth and

(a) Place the ends of the tubes side by side in a pan of water. Describe what takes place in the tubes 1. Does the water rise on the inside. of each tube or does It rise on both the inside and outside ? 2. If two tubes are placed side by side and as close together as possible, what effect has this on the rise of water between them?

(b) Into a small wide mouth bottle or evaporating dish, pour alcohol or kerosene until it stands about Hm deep. Fill the bottle with dry sand or finely divided air-dry soil and press down firmly. Let stand for about it) minutes, then apply a lighted match. Result? What does this show? This experiment represents accurately the capillary rise of water in soils to replace that used by the plant or that lost by evaporation.

(c) Number and weigh four pans, and place in each o± two 50 grams of soil, and in each of the remaining two 50 grams of subsoil. With a pestle or glass rod break up all lumps, at the same time spreading the soil evenly on the bottom of the pans. Set aside and leave undisturbed until the next laboratory period Weigh again and continue to weigh at each successive period until the weights become constant. Compute the percentage of capillary moisture on the basis of water free soil as found in Exercise 4. The difference between the total moisture and the amount of capillary moisture represents the hygroscopic moisture of soil. Calculate the per cent hygroscopic moisture in the samples under consideration.

(d) Close one end of each tube using a piece of cloth and tying with a string. Fill the tubes with finely divided air-dry sand, sandy loam, loam and clay. Do not separate the coarse and fine particles. Compact the soil by letting the tubes drop onto a book, taking care to let the tubes drop the same number of times and the same distance. Support the tubes so that the ends dip about one inch in water in the bottom of a pan. Observe the height to which the water has risen at the end of 1 hr., 2 hr., 4 hr., 6 hr.. at the next meeting of the class, and at each meeting thereafter for two weeks or more. Keep a paper by each tube showing 1, the height of the moisture, 2, time and day of each reading. Record results in tabular form in your note-book.

Questions: 1. Which tube shoAvs the most rapid rise? 2. At the end of an hour, which shows the greatest rise? 3. At the end of a wpek? 4. What effect does size of particles have on rapidity of movement?

6. EFFECT OF DRAINAGE ON SOIL TEMPERATURE.

Materials: Five-gallon oil can with one side removed, wooden box approximately the same dimensions.

Fill each with the same kind of soil and apDly the same amount of water until drainage begins in the box. There will be no drainage from the can. If necessary, loosen a board in the bottom of the box. Let the two stand out of doors until the following day. Begin as early in the morning as possible and take thf temperatures hourly at depths of 1 and 3 inches until 5 P.M. Record results on a piece of paper left by the vessels.

Let some pupil who lives near wet land record the temperatures of this land together with the temperature of adiacent drv land at convenient intervals some Saturday. Compare his temperatures with those of the experiment. Tabulate the results. Give explanations for differences in temperatures.

Question: If drainage effects the temperature, how may it affect a crop ?

MANUAL OF GENERAL AGRICULTURE.

7. EFFECT OF COLOR ON SOIL TEMPERATURE.

Materials: Two cigar boxes, soot, slaked lime, two thermometers, seeds.

Place well pulverized moist soil into two cigar boxes, filling them about half full. In one-half of one box, bury twelve seeds i/o inch deep, using bean, corn, wheat, or any other quick germinating seeds which may be on hand. In the other half plant 12 seeds of some other plant. Cover both plantings with chalk dust, slaked lime or white ashes to a depth of 14 inch.

In the same manner plant the same number and the same kinds of seeds in the other box, but instead of using light colored covering, use soot.

Each time the class meets after the second day observe the number of plants showing above the surface, keeping a record of the dates and kinds sprouted on the side of the box. In the morning of a clear day insert a thermometer into each box to about the depth of the sprouted seeds. After a few minutes, when the thermometers have become ad.justed to the new temperatures, take the readings. Continue to take the readings hourly throughout the day. Record the results as follows :

DAYS TO SPROUT

TEMPERATURE

Light Soil

Dark Soil

Time

Light

Dark

Soil

Soil

Question : Which soil shows the higher temperature ? Why?

MANUAL OF GENERAL AGRICULTURE.

8. EFFECT OF EVAPORATION ON SOIL TEMPERA- TURE.

Materials: Two tomato cans, 2 thermometers, plotting paper.

Fill two tomato cans with air-dry soil and saturate one with water. Bury the cans side by side in a sunny spot, leaving about I/2 inch of the tops above the surface. Insert a thermometer into each to a depth of about 1 inch. The following day as early as possible take the first reading and continue taking readings every hour thereafter until 5 P.M. On plotting paper draw a curve of temperature for each can, using TIME and TEMPERATURE for the co-ordinates as shown in the diagram.

TIME

11 12

How to plot the curve. Suppose at 8 o'clock it was found that the temperature of the saturated soil was 61 degrees F., a dot should be placed half way between 60 degrees and 62 degrees on the 8 o'clock line ; if at 9 o'clock the temperature was 61.5 degrees, the second dot should be placed Y^ of a division higher on the 9 o'clock line. Continue to put dots for all your temperatures. Connect the dots by a straight or broken line.

9. PER CENT OF AIR IN SOILS.

Materials: Three beakers or bottles, graduate, sand, clay, and loam.

Put 25 cc. of sand in one beaker, 25 cc. of clay in the second, and 25 cc. of loam in the third. Fill the graduate to the 50 cc. mark with water and pour on to each sample until the water just rises to the surface. The amount of water required is an approximate measure of the air space, since the water displaces the air. Figure out the per cent of air space in each sample.

Question: What effect does size of patticles have on total amount of air space?

10. SEPARATION OF SAND, SILT AND CLAY IN

SOILS.

Materials: Tall beaker of about 500 cc. capacity, flask with long narrow neck, mortar, rubber pestle made by inserting a glass rod into a one-hole stopper.

Weigh out exactly 20 grams of air-dry soil and place it in a mortar; add 12 cc. water and rub with the pestle. Let it settle a minute and pour off the muddy water into the tall beaker. Add more water to the mortar and repeat until the water in the mortar no longer gets muddy. The part remaining is coarse sand.

With small amounts of water wash the sand from the mortar through a funnel into a long necked flask.

Add water to the beaker containing muddy water until it is nearly filled. Stir and let stand for an hour, or until the next meeting. The muddy appearance of the water is due to the clay, which remains in suspension. Siphon off without disturbing the sediment and keep both the siphoned portion and the residue. Fill the beaker again with water, stir, let settle an hour and siphon as before. Repeat until after standing an hour the water above the sediment is clear. Add the siphoned portion to that obtained before. Transfer the sediment to the flask containing the sand. Nearly fill with water and stopper well. Shake and invert on a ring-stand so that the neck is perpendicular. After the small particles have settled, note the different layers of sand at the bottom, to fine silt. Ascertain approximately by volume the percentages of sand, silt and clay.

11. WATER HOLDING CAPACITY OF SOILS.

Materials: Air-dry sand, clay, loam, three student lamp chimneys, cheesecloth, string.

Tie a piece of cheesecloth over the bottom of a chimney, moisten the cloth and weigh accurately. Fill the chimney with dry sand and compact by dropping onto a book a counted number of times from the same height. Weigh it again and stand it in a trough containing several inches of water. Leave it in this position until the surface of the sand becomes thoroughly moist. Remove the tube, wipe dry, and weigh again. Cover the tube with cotton and set it where the water will drain away. "Weigh later in the day and at each meeting of the class thereafter for at least 5 days. In the same way prepare tubes using clay and loam or any other soil.

If the soil used is very dry there should be no capillary moisture, but the hygroscopic moisture is still in the samples, hence the results will be too low. For more accurate results the hygroscopic moisture should be determined. Express your results in tabular form.

Questions: 1. Which soil loses water more rapidly? 2. Which takes the longest time to percolate?

12. EFFECT OF HUMUS ON WATER HOLDING CAPACITY OF SOILS.

Materials: Three tin cans, dry well-rotted manure.

Perforate the bottoms of three tin cans. Place a piece of cheesecloth on the bottom of each and weigh, recording the weights on the outside of each. Place in one 95 grams of sand, and 5 grams of well-rotted manure ; into another 85 grams of sand and 15 grams well-rotted manure ; into the third 75 grams sand and 25 grams well-rotted manure. Saturate each with water and weigh immediately. Write results in each case as follows :

Sand containing 5% organic matter retained — % moisture, etc.

13. EFFECT OF MULCHES AND CULTIVATION ON EVAPORATION FROM THE SOIL.

Materials: As indicated in exercise.

Secure three five-gallon oil cans and cut them in half with a can opener. In case the upper half of any one cannot be made water-tight another must be used. Place an inch of gravel in each. Place in the corner of each a student lamp chimney.

Fill each can with soil to within two inches of the top, slightly compacting the soil. Number the cans from one to six. Cover the soil in number five with one inch of sand. Cover number six with one inch of stable manure.

Weigh each can and record its weight. Bury the cans in an open place until the surfaces inside and out are on the same level. Place them in a row according to numbers and about two feet apart. Pour into each chimney a measured amount of water, allowing time for the soil to absorb it. When the cans without a mulch show dampness on top discontinue. Continue the experiment as follows:

No. 1, check, let alone.

No. 2, cultivate one inch deep once a week.

No. 3, cultivate two inches deep once a week.

No. 4, cultivate three inches deep once a week.

No. 5, let alone. No. 6, let alone.

Continue the experiment at least six weeks, adding measured quantities of water to the cans as they need it to keep the surfaces in good condition for crop growth. At the end of the required time dig up the cans, wipe the outsides clean and weigh. Add to the original weight of each can of soil, the weight of the water added, and subtract from the result the last weight of the can. The difference represents the amount of water evaporated. Tabulate the results.

Questions: How may a farmer obtain an artificial mulch ? A natural mulch ?

14. EFFECT OF VEGETABLE MATTER ON THE CAP-

ILLARY RISE OF WATER.

Materials: Air-dry soil, sawdust, well rotted manure, tubes as indicated in experiment.

Obtain three glass tubes about an inch in diameter and two feet long. Close the ends of each by means of cheesecloth firmly tied on. Fill one tube with well pulverized air-dry soil and compact slightly. Into a second tube place the same kind of soil to the depth of one-half its length, and then place a two-inch layer of sawdust, and finally fill to the top with soil and compact as above. In the third tube use finely divided well-rotted manure in place of sawdust. Place the tubes so that the lower ends stand about an inch deep in water. At the next laboratory period notice the rise of capillary water. Leave for another laboratory period, at which time write up the experiment and put away the apparatus. Assuming that the crop roots go below the straw or manure plowed under, state the effect of plowing under a large amount of straw or poorly rotted manure.

15. EFFECT OF A MOIST ATMOSPHERE ON DRY

SOILS.

Materials: Sand, clay, loam, 3 fruit jars, 3 small receptacles to hold water and small enough to go into the jars, scales.

Place 100 grams of air-dry sand in an accurately weighed fruit jar. Place in the jar a small receptacle containing water. Tightly close the fruit jar and set in the sun. Repeat, using clay and loam. Weigh at each laboratory meeting thereafter until the weight becomes constant. Remove the receptacle at each weighing.

Calculate the amount of moisture absorbed in each case. These amounts are not the total moisture since the hygroscopic moisture was always present.

Questions: 1. Which class of soils absorb the largest amount of moisture, and why? 2. If soil absorbs so little moisture from a saturated atmosphere ; why do wilted plants "freshen" on a foggy morning?

16. EFFECT OF LIME ON SOILS.

Materials: Clay or clay soil, 2 cigar boxes, slaked lime.

Prepare four moulds one inch in width and the length of the width of the cigar box. Use pieces of one cigar box for the partitions in the other, thus having the four moulds in one box. Weigh out four 100 gr. samples of clay soil and add the following amounts of well-pulverized slaked lime :

No. 1, add none.

No. 2, add one gram.

No. 3, add five grams.

No. 4, add ten grams.

Mix each sample thoroughly in a pan, then add just enough water to make the soil plastic. Mould each sample into a form of a stick by compressing the moist clay in the moulds. Leave in the sun at least a week, or bake in an oven until thoroughly dry. Remove the sticks and determine the weight necessary to break each in the following manner :

Rest the ends of a stick of clay upon supports and suspend from its center a bucket into which sand is slowly poured.

Tabulate the results.

Questions: 1. How does lime effect the tenacity of clay? 2. What effect on the physical condition of clay has lime?

17. ONE EFFECT OF HUMUS, OF SAND, AND OF

LIME, ON A CLAY SOIL.

Materials: Four pans, clay, slaked lime, sand.

Fill four pans i/4 Ml of clay and treat as follows :

To the first add enough water to saturate the clay. Make a note of the amount of water used.

To the second add about V2 its volume of humus or fine, dry, well-rotted manure, and the same amount of water as before.

To the thir water, the same as before.

To the fourth add i/^ its volume of sand and the same amount of water as before. Make each into a ball and set aside to dry. In a few days examine and see which one can be more easily pulverized with the fingers.

Questions: 1. State the conclusions as to the value of humus, sand, and lime on a clay soil as shown in this experiment. 2. What causes a clay soil to bake. 3. How can the baking of a clay soil be prevented?

18. DETERMINATION OF THE SPECIFIC GRAVITY

OF SOILS.

Materials: Graduated cylinder (25 cc. or 50 cc), sand, clay and loam soils.

In this experiment we are to compare the weights of different soils with the weights of equal volumes of water. Ascertain the weight of 10 cc. of water. Place exactly 10 cc. of water in the cylinder, reading to the top of the column but not including the crescent formed on the surface of the column. This water crescent is called the "meniscus." Pour 10 grams of accurately-weighed sand which has been dried to a constant weight into the water. Shake to expel the air. Take the reading as before, not including the meniscus. Subtract 10 from this reading, and the remainder is the volume of water displaced by the sand. Determine the weight of displaced w^ater and calculate the specific gravity according to the following formula:

Wt. S.

Sp.=

Wt. w.

in which Sp.^=specific gravity, "Wt. S.=weight of sand or soil, and Wt. 'W.=weight of water displaced. Calculate the specific gravity of clay and loan soils.*

Questions: 1. What is specific gravity? 2. Why is it necessary to use water-free soils? 3. How does the amount of humus affect the specific gravity?

The specific gravity of the material which forms the great bulk of most soils is about 2.6. But the soil is not a solid mass. It is composed of spherical particles which touch each other at different points. About 50% of a cultivated soil is air-space. Hence this air space reduces the weight of a volume of soil much below the specific gravity of its constituents. In this experiment we really found the specific gravity of the constituents, which is termed "real specific gravity." In the following experiment we are to determine the specific gravity, including air-space, which is termed "apparent specific gravitj^"

19. DETERMINATION OF APPARENT SPECIFIC GRAVITY OF SOILS.

Materials: Same as in last experiment. In this experiment we are to determine the ratio of unit weight to unit volume of different soils.

Pour into a dry cylinder 10 cc. water-free sand. Weigh the sand. Having already determined the weight of 10 cc. water calculate the apparent specific gravity according to the following formula :

V. S.

Sp.=

V. Wt. w.

Wt. S.=weight of soil (i.e., weight of 10 cc. soil), V. Wt. W.^weight of water (i. e., weight of 10 cc. water).

Questions: 1. What influence have stones upon the apparent specific gravity? 2. What influence has plow-

*In general when cubic centimeters and grams are used the specific gravity of a body is found by the formula: