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1844. THE CIVIL ENGINEER AND ARCHITECT’S JOURNAL 109 AGRICULTURAL CHEMISTRY. By Professor Brande, F.R.S., &c. Lecture IV.—Delivered at the Royal Institution, Feb. 17, 1844. C Specially reported for this Journal.) Phosphoric acid, once considered unimportant, is requisite for most crops, but especially for wheat and grass. It is generally added to the soil in com bination with lime, as bone dust, the earthy part of bone consisting almost entirely of phosphate of lime. Phosphorus, the base of phosphoric acid, is never found in a free state in nature, being obtained by distilling a mixture of phosphoric acid and charcoal. It is a pale yellow semi-transparent solid, remarkable for its easy combustibility, luminous in the dark, owing to its slowly burning. When set fire to and a tall glass jar placed over it, flakes of a beautiful white substance are collected, which is phosphoric acid, the phosphorus having combined with the oxygen of the air. These flakes will, in a short time, abstract moisture from the air, and become liquid. If this liquid be then added to a solution of lime, phosphate of lime, or bone earth, falls as a fine white insoluble powder. When bones are burned, it is this which is left as the white ash, the animal matter having been destroyed. But as phosphate of lime is soluble in acids, the animal part may be obtained in a separate state by digesting bone in weak muriatic acid ; the bone remains in its original shape, but is then as flexible as cartilage, the whole of the earthy part being removed. In this state it is that bones arc employed to make animal glue and portable soup. Formerly it was supposed that it was to this part that the virtue of bone manure was due; but it is found that bones are nearly as efficient after the animal part has been destroyed, as for instance, after they have been distilled for the manufacture of hartshorn, or ammonia. Since this has been clearly established there has been great demand for phos phate, search has been made to ascertain whether any large natural supply of this substance could be discovered, as it is frequently found in a mineral state. For this purpose Dr. Daubeny made a pilgrimage to Spain, and in Estramadura he foundalarge quantity known as Phosphorite, from its giving off a pale blue light when heated ; but as there is no water conveyance from thence, and the roads are bad, the expense would be too great. It is present in nearly every soil, and is even to be found in chalk, as the following analysis of the Brighton chalk will show. 100 of Brighton Chalk. Carbonate of lime . 98-57 Carbonate of magnesia. . 0-38 Phosphate of lime . 0-11 Oxides of iron and magnesia. . 0-14 Alumina . 0-16 Silica . . . . . 0-64 100-00 In slate, phosphoric acid sometimes exists combined with alutnina, and oc casionally the surface of the slate is found covered with a crystalline mass of phosphate of alumina, or wavellite, as mineralogists term it. When this dis integrates, to form a clay soil, the phosphoric acid will get diffused, and thus become one of the elements of the food of the plant. In the chalk, which is agreed by most geologists to be the debris of organic matter, the phosphoric acid has, no doubt, had its origin from the shells of come of the lower animals. An interesting observation has been made on this subject, viz., that the shelly or bony structure of the lowest animals consists wholly of carbonate of lime; that as they increase in complexity of structure, a little phosphate of lime is found, and in that of the animals highest in the scale of creation, phosphate has entirely replaced the carbonate of lime. From this fact, the absolute necessity for phosphoric acid in the soil is evident; for the growing animal, browsing in the field, is continually adding phosphate of lime to his increas ing bone ; from whence can it come ? As he eats nothing but plants, it must be in their structure, and analysis proves it to be so: then, again, as the plant derives all it contains from the earth, air, and water, it must be in one or other, and the analysisof all fertile soils shows that it is invariably present. These remarks applying to phosphoric acid, are applicable to all the inorganic constituents of animals or vegetables. But it is also requisite that they should be in a soluble state, or the plant cannot take them into its circulation, and frequent disappointment has arisen in the use of bone dust, from there having been nothing in the soil to dissolve the phosphate of lime ; it is by some imagined that plants excrete from their roots acid substances to render soluble the substances around them. Experiments have been made by dissolving the phosphate in an acid previous to mixing it with the soil, and very beneficial results have been obtained. The Duke of Richmond found that a much larger crop of turnips rvas thus obtained, and some agriculturists have stated that one pound of bone dust mixed with acid is as efficacious as 61b. without. The proportions advisable are, to take 1001b. of bones, and after breaking small, to add to them about 501b. of sulphuric or muriatic acid, they being the cheapest, and about three cwt. of water, which will give a solution of sub phosphate of lime and free phosphoric acid. In order to get it into a con venient form for application, it is advisable to sprinkle this liquid over some substance which will absorb it, such as saw-dust; if to this be added some silicate of potash, a most fertilising agent is obtained. A manure which is now being very extensively employed in this coutry, and the demand for which is daily on the increase, viz., guano, appears to owe its qualities prin cipally to the phosphate and other salts which it contains. It is the excre ment of sea birds, and is obtained in immense quantity. The amount of in organic matter it contains may be ascertained by burning a known weight in a silver crucible, and weighing the ash which remains. The quantity of inorganic material requisite to be added to the soil will depend upon two things, the quantity that the plant absorbs to form part of its system, and also upon what part of the plant is removed from the field, as it has already been seen how greatly the various parts of a plant differ in the quantity of their inorganic constituents. Hence is evident the importance of ploughing in all the parts of the plant not taken to market, especially the leafy parts. It is even, in sandy soils, found advisable to burn the plants which have grown there, such as heath and furze, and to return the ashes, which, by this means, in a few years render it fit for the growth of more profitable crops. The great difference in the quantity of the salts which various plants appropriate, will be rendered very evident by the two following tables:— Salts, 8{c. in 1000 of the Ash of Seed and Straw. Wheat. Wheat Straw. Barley. Barley Straw. Oats. Oat Straw. Beans. Bean 1 Straw. 1 Potash 190 5 120 35 60 150 195 530 ' Soda 203 7 120 10 50 380 15 Lime . 80 70 45 105 30 27 77 200 ■ Magnesia 80 10 80 15 25 5 75 67 Alumina 20 28 10 30 5 — 15 5 Oxide of Iron — — — 5 15 — — | Sulphuric acid 40 10 25 20 15 15 40 10 Phosphoric acid 35 50 90 30 30 3 138 73 Silica . 340 810 500 735 765 800 60 70 Chlorine 10 10 10 15 5 — 20 25 Composition of Three Soils. Silica 7767 9214 8465 1 Alumina . 445 149 50 Oxides of Iron . 515 308 82 Oxide of Magnesia 83 31 3 Lime 212 59 13 | Magnesia . 153 36 7 Potash and Soda 24 14 2 Phosphoric acid 68 6 13 Sulphuric acid . 56 1 1 Chlorine . 4 2 3 Organic matter . 247 106 1200 9574 9926 9839 Less 426 74 161 10,000 10,000 10,000 ! This will serve to explain why those plants which contain but few of these salts are said to form good fallow crops. It is remarkable, also, the invariable proportion in which they are present in the same plant, although grown in a different climate, and in a different soil. Sprengel analysed wheat from several districts, and found them, in this respect, exactly to resemble each other. A question has arisen amongst vegetable physiologists whether me sub stance usually present in a plant, can be substituted by another, and it has been found to take place in some few instances. For instance, cases ha.e occurred where plants which usually have one alkali present, when grown in a soil where that alkali is not present, have been found to appropriate another, but still preserving the same amount. Indeed, some plants, when growing in circumstances where they cannot obtain inorganic alkalis, will positively form organic ones, in order to carry on their functions; such is said to be the origin of the morphia, in poppies, to which organic alkali the properties of opium are due. It is well known that potatoes when stored up in a damp cellar, will throw out shoots to a very great length. Now when these are analysed, they are found to contain a vegetable alkali in great abundance, to which the name of solanine has been given, not an atom of which is ever to