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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[March, 



be found in Ihe plant in Us natural state. It has, in fact, formed this alkali 

 from some of its otlier constituents, so that its germinations may proceed. 



The efTtcacy of common salt as manure is most undoubted in many situa- 

 tions. To lands near the sea there cannot be any necessity for adding it, as 

 the winds carrying the spray always give it a top dressing of salt, and those 

 near the shore generally get too much. It is said by some to render the 

 silica soluble, but one undoubted benefit it bestows is in killing the grubs and 

 vermin which infest some crops to so enormous an extent. It is present in 

 every soil. It is used in sreat quantities for the manufacture of soda, and 

 distilled with sulphuric acid, yields muriatic acid. 



The very hrge proportion of inorganic constituents thatlsome plants con- 

 tain, is occasionally rendered evident by accident. Thus hay, which contains 

 90 per cent of its weight, is frequently found, when a rick has caught fire, to 

 be converted into a hard opaque glass, and a com stack will burn to a com- 

 plete tlint. In the case of hay, this accident sometimes occurs, when it has 

 been stacked before it is dry, by the heat which is evolved during the fer- 

 mentation of its juices. There is a very admirable arrangement in nature for 

 returning to the soil, every year the inorganic substances which it requires 

 for its growth, but which it has not retained in its wood, and that is the 

 autumnal fall of the leaf, which, as has been already seen, contains, of all 

 other parts, by far the greatest quantity of salts. Thus they serve to go one 

 perpetual round, now dissolved by the water in the soil, and absorbed by the 

 roots, now flowing with the sap through every ramification of the tree, and 

 at last forming part of the leaf, to be on the approach of winter, again de- 

 posited on the soil, to be again dissolved, absorbed, and perform the same 

 functions ; but in each circuit leaving part of itself as a permanent resident 

 in the stem of the plant. Thus, then, we are led, by a consideration of these 

 and other circumstances, to the only inference that can be drawn, that these 

 inorganic constituents, in small proportion to the other parts as they maybe, 

 are nevertheless vitally essential ; that no substance found in the ash of a 

 plant can be considered as accidental but as constitutional, without every one 

 of which be present in the soil, and in a fit state, it is useless to expect the plant 

 to show, when the deficiency of the soil is known, what is requisite to be 

 added, so as to make it suit each respective crop. 



But it is time to pay attention to the organic part of the soil. This, which 

 consists of the vegetable mould formed from the decay of the woody parts 

 of the plants, is known by the name of humus. It may be traced in various 

 stages, from the firm wood, to the yellow rotten wnod, then to a brown, and 

 lastly to a black earth, which is almost charcoal. On the banks of a stream, 

 shaded by overhanging trees, the fallen beams may frequently be seen in the 

 medium state, whilst at the bottom of the water, the dark brown mud is the 

 best instance of it in its final state. When stirred it frequently gives off car- 

 bonic acid and carburetted hydrogen, arising from the decomposilion of the 

 woody fibre, or eremacausis, as it is the fashion to term it. There is no 

 doubt that the presence of this is beneficial in the soil, though not to the ex- 

 tent that it was formerly considered. As it is very slightly soluble in water, 

 it cannot yield much nourishment to the plant, and it is doubtful, except by 

 the carbonic acid which it slowly evolves, whether it is of any other than a 

 mechanical advantage to the soil. Indeed it is the opinion of many, that so 

 long as the plant can get its inorganic parts from the soil, it can derive all 

 its organic parts from the atmosphere. Vegetable matter, however, is found 

 in all fertile soils, in the proportion of from 10 to 20 per cent. In boggy 

 earth, it forms from 60 to 70 percent. For the growth of rice, but little is re- 

 quired, for barley more, and for wheat more ; abnut 12 per cent, is advisable. 

 Water poured on good soil, should be very slightly coloured ; if deep brown, 

 it will be barren, possibly arising fron the presence of an acid, rendering the 

 vegetable matter soluble ; this must be counteracted by lime or chalk. 



Soils are classified and named according to the proportion of their principal 

 constituents; thus some consist of pure agricultural clay, of which pipe clay 

 is a good example, which consists of from 50 to CO of silica, the remainder 

 being alumina. This when stirred up with water, deposits no sand. Rivers, 

 passing through clayey soils, carry with them an immense quantity, taking 

 weeks to deposit the whole, and in some cases carrying it a long way out to 

 sea. When a clayey soil contains 



From 5 to 20 per cent, of sand, it is called a strong clay. 

 „ 30 to 40 „ „ clay loam. 



„ 40 to 70 „ „ loam. 



„ 70 to 90 „ „ sandy loam. 



90 ,, ,, sandy soil. 



Whc 1 chalk is present in from 5 to 20 per cent , these are termed marls ; and 

 are sandy, loamy, or clayey, according to proportions. More than 20 per 

 cent, forms a calcareous soil. 



From 5 to 20 per cent, of humus constitutes a vegetable soil, and from that 

 to 70 iwr cent, a peaty soil. 



Lectcre v. 

 Twenty years ago, when the agricultural chemist was requested to analyze 

 a soil, he would consider he had done his duty when he had ascertained the 



proportions of the four earths, and the organic matter. Now, however, the 

 case is widely difierent, and it has become one of the most complex opera- 

 tions, which can be performed only by an experienced hand, and wiiich it is 

 of no use for the farmer to attempt ; for it is very doubtful whetlier, if he 

 became an expert chemist, he would also be an expert agriculturist. Siill, 

 however, the knowledge of the use of the various tests set forth in these 

 lectures ought to be possessed by every agriculturist, they are soon acquired, 

 and will give very valuable information. 



In order to classify soils, the usual mode of examination is as follows:— 

 Weigh a certain quantity of soil, dry in air, then reduce it to powder, and 

 dry It before a fire on paper, at as greats heat as the paper will bear w ilhout 

 charring, then weigh it to ascertain the quantity of water lost ; burn it in a 

 crucible fur the purpose of destroying organic matter, and again weigh it ; 

 then put in dilute muriatic acid, about 1,000 grains of the soil to a pint of 

 water and two ounces of acid, which will dissolve the saline ingredients, dry 

 it before a fire, and weigh it, then stir it up in a considerable quantity of 

 water, and whilst the finest particles are suspended, pour off the water, and 

 by this means the clay will be separated, 



A soil may have every ingredient requisite for vegetation, and yet not be 

 productive on account of its not being in a proper mechanical condition, and 

 there are several particulars to be looked to in this respect, such as density, 

 division, retention of water, capillary power, shrinkage, relation to heat, 8tc. 

 All these demand consideration. 



A soil should not be too dense, as it then offers too great a resistance to 

 the growth of the plant, retains water too firmly, and, consequently, is always 

 cold. The weight of a cubic foot of good soil should be from 50 to 90 lb. The 

 state of division of a soil should be tolerably fine, though occasionally large 

 masses are of use. It is the custom to gather oft' the large stones from a 

 field, but during cold or dry winds they are of service by protecting the 

 tender plants from the nipping of the one or the parching of the other. The 

 state of cohesion of a soil should be between the looseness of sand and the 

 plasticity of clay. This may be considerably modified by deep ploughing, by 

 tilling, but particularly by draining. In very clayey lands, the best thing to 

 do would be to add sand, but as that would be generally too expensive, the 

 best substitute is drainage. The resistance to the plough varies very much 

 according to the nature of the soil. It has been calculated that sand gives a 

 resistance of about 41b. to the square foot, clayey ground about 81b., and a 

 stiff clay about 251b. 



Soils diller in nothing so much as their power of imbibing and retaining 

 water. It has been found, by direct experiment, that exposed for twelve 

 hours in damp weather, 1,000 lb. dried sandy soil gained 21b. ; 1,0001b. dried 

 loam gained 21 lb. ; 1,0001b. dried clay loam gained 251b. ; and 1,0001b. dried 

 pure clay gained 37 lb. 



According to some experiments of Sir H. Davy, the same quantity of a 

 barren sandy soil gained 31b. in twenty-four hours, whilst a fertile soil gained 

 181b. This will give some idea of the enormous quantity of moisture that 

 would be absorbed from a moist air following a dry wind. Mr. Solly has 

 made some experiments on increasing the imbibing power of dry soils, by 

 adding- to them some very deliquescent substance ; for this purpose he used 

 chloriile of calcium with very good results, Connected with this is its re- 

 taining power. A quantity of water which would soak sand, would scarcely 

 moisten dry clay. They have been found to vary as follows : — 100 lb. of sand 

 retained 251b. of water; loam, 401b.; chalk, 4olb. ; marl, 501b.; and agri- 

 cultural clay, 701b. The moister the land, of course tlie more imperative it is 

 to drain it well, as too much water keeps a soil cold, and prevents the air 

 from getting to the plants. 



Capillary attraction, or that power by which liquids crawl up small cre- 

 vices, is exceedingly influential in agriculture, and is beneficial in two ways j 

 1st, by keeping the surface in a proper state of moisture, bringing up water 

 from below, as fast as it evaporates above. This action may be illustrated 

 by standing a lump of salt or otlier porous substance on end in a plate filled 

 with a coloured liquid. It takes place very rapidly by using a tall glass 

 cylinder, having a porous bottom, filled with sand. The densest chalk that 

 can be procured will, in this way, become coloured several inches high in a 

 few hours. In horticulture it is frequently taken advantage of by keeping a 

 flower-pot in a saucer, into which water is poured. The second important 

 use of capillary attraction is to bring up from the sub-soil a supply of those 

 soluble substances of which the removal of the crops is continually depriving 

 the soil. This may be thought but trilling, but when the immense amount of 

 water evaporated is taken into account, it will appear far from insignificant. 

 After a continuance of dry weather, the soil will frequently be covered with 

 a perceptible film of the salts thus brought up, which by the first shower is 

 diffused through the soil. In sandy lands the fertility depends upon this 

 property. In tropical climates, where evaporation is so much greater, it is 

 seen on a magnificent scale. In the deserts of Peru, for instance, the nitrate 

 of soda thus annually brought to the surface is raked off, and exported in 

 immense quantities, to be used for manufacturing, and latterly for agricul- 

 tural purposes. In Africa, also, the neighbourhood of Tripoli thus furnishes 

 a supply of a variety of carbonate of soda. These facts induce the inquiry 



