This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
The following is a minimum list of apparatus, some of which may be evolved from ordinary articles in everyday use, but the majority will need to be specially designed, or accuracy in results cannot be looked for: -
1 balance. Palette knife.
Beakers. 6 at 300 cub. cm. capacity. 2 at 600
1 Winchester quart for citric digestion. CO2 apparatus.
2 Berlin porcelain dishes, 4 in. 4 „ „ crucibles.
1 distilling flask and condenser.
1 closed vessel to supply steam, to act as small boiler.
2 conical flasks with Bunsen valve. 2 burettes, 50 cub. cm.
1 pipette, 25 cub. cm.
1 graduated measure, 500 cub. cm.
1 „ 100 „ 6 clockglasses.
2 filtering funnels, 4 in.
2 filtering funnels, 6 in. 1 stoppered cylinder, 750 cub. cm. 1 desiccator.
1 wash bottle for water. 1 „ „ alcohol.
1 „ „ ammonia.
1 „ „ hydrochloric acid.
1 „ „ nitric acid.
1 pestle and mortar. 6 glass rods.
1 large sieve, 4 meshes to inch. 1 small „ 16 „ „
Filter stand. Water bath. „ oven. Burette stand. Filter papers. 1 pair crucible tongs.
The first constituent to be estimated will be the lime carbonate in the soil. Proceed as follows: Place a small quantity of soil in a test tube or other convenient vessel, such as a cup; fill up to 1 in. from bottom; pour over sufficient strong hydrochloric acid (commercially known as spirits of salt) to cover the soil. If the soil contains a reasonable amount of lime carbonate a vigorous effervescence will occur, but if there is little or no disturbance then lime or lime carbonate must be added to the soil at once. The chemical action is roughly as follows: Hydrochloric acid (HC1) attacks the calcium carbonate (CaCO3), driving out carbonic acid gas and forming calcium chloride.
The more accurate method adopted by chemists is as follows: -
To estimate the available constituents of the soil, 200 gm. are mixed with 2000 cub. cm. of 1-per-cent citric acid solution and left for a week, the whole being shaken up once a day. The solution is then filtered and divided into separate portions of 500 cub. cm.
To estimate the soluble phosphates 500 cub. cm. are evaporated until the volume is reduced to about 100 cub. cm. and then allowed to cool, and 40 cub. cm. of ammonium molybdate solution added, well stirred, and allowed to stand in a warm place. This is then filtered and the precipitate washed, first with dilute nitric acid and then with very small quantities of distilled water. The precipitate is then dissolved in ammonium hydrate and 20 to 30 cub. cm. of magnesia solution added, the whole being allowed to stand for twelve hours for complete precipitation. The resulting precipitate is now filtered off and washed with dilute ammonia dried and incinerated in a crucible, the residue being weighed as magnesium phosphate. From the magnesium pyro-phosphate obtained the weight of phosphoric acid can be calculated. One part of magnesium pyro-phosphate = .64 parts of anhydrous phosphoric acid (P2O5).
Total phosphates are estimated by treating 5 gm. of dried soil with 25 cub. cm. of concentrated hydrochloric acid, and evaporated to dryness over a water bath. The residue is moistened with concentrated sulphuric acid, then treated with a mixture of 10 cub. cm. of hydrochloric acid and 10 cub. cm. of water, warmed, filtered while hot, the filter paper being well washed, and the filtrate treated with an excess of ammonia, boiled, allowed to cool, and filtered. It is then redissolved in nitric acid and dried with 40 cub. cm. of ammonium molybdate exactly as indicated in the paragraph above for soluble phosphates.