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THE FARMER'S MAGAZINE. 



the different substances, whether simple or com- 

 pound, and incapable of being reduced mechanically, 

 and of which the properties are often different and 

 sometimes opposite to the former constituents. 

 This affinity of composition is one chief agent in 

 the operations of nature and art, and the ease and 

 rapidity with which bodies are decomposed, or 

 enter into new combinations, are directly as the 

 quantity of the surfaces which they present, or 

 inversely as their masses. The efficacy of com- 

 position is inversely as the attraction of adhesion : 

 the absolute force remains the same, but increases 

 on account of the diminution of the opposing at- 

 traction. Electric attraction is the principle in ac- 

 tion, and chemical affinity is the power by which 

 bodies unite, the one being in this sense a measure 

 of the other. All chemical forces are subordinate 

 to the cause of life, and to heat and electricity, and 

 to mechanical friction and motion. The latter 

 power is able to change their direction, increase or 

 diminish their tendency, and also completely to 

 stop and reverse their action. Causes must exist 

 to produce chemical affinity, or the cycle of life 

 would stand still ; and from our ignorance of these 

 causes and of the application, it is probable that in 

 many cases their action is arrested and stopped, 

 often rendered useless, and not produced at all, or 

 at best but accidentally. Bodies that have httle or 

 no affinity, and do not enter into combinations, are 

 made to do so by the addition of one or more sub- 

 stances ; and this principle shows the necessity of 

 applying a number of substances at one time, and 

 of bringing them into contact with each other in a 

 state of minute adherence. Many kinds of chemical 

 action are effected by heat, electricity, and other 

 agencies, over which any control is impossible, and 

 which do not take place from mere comminution 

 and mixture, yet by that process a ready accession 

 of means will be afforded of producing combinations, 

 which in another state of existence of the sub- 

 stances would not have happened. Science shows 

 that quantity is necessary in many cases to produce 

 any combination whatever, for an increase of 

 quantity is known to be equivalent to a superior 

 affinity ; and though no rule has yet been obtained 

 in respect of the quantities to be used in each par- 

 ticular case, yet the strongest presumptions may 

 be drawn in favour of the above conclusion being 

 generally applicable. 



The maxims of chemistry that have now been 

 quoted are quite decisive in showing that all bodies, 

 from whose union and combination the benefits of 

 new formations are expected, must be brought into 

 contact in a state of comminution, and must be 

 very intimately mixed, in order that the distance 

 may be insensible between the molecules of the 

 different bodies which produce the reciprocal action. 

 Though one general principle produces the opera- 

 tion, it is very much influenced by various causes, 

 as the quantity of the substances or bodies, and by 

 temperature in a great degree, by electricity, and 

 by mechanical pressure, by insolubility, and by 

 other causes arising from peculiar circumstances. 

 One body at least must be in a state produced by 

 solution or fusion: water or some liquid is necessary 

 to produce a heterogeneous affinity, and the union 

 results from the reciprocal action of the molecules 



of the two bodies on each other. Different effects 

 are accordingly produced on different objects in 

 different situations, and the quantity and degree of 

 the exertion of the power depends on various and 

 changing circumstances ; for bodies in changing 

 state also change capacity. A knowledge of the 

 phenomena of nature, shown in the order and 

 mutual dependence of combinations, would enable 

 us to make them subservient to the improvement 

 of the arts, and direct them to the useful purposes 

 of life. It may be very fairly questioned if agricul- 

 ture has yet derived the one-half of the benefits of 

 comminution and mixing of the soil with the sub- 

 stances that are used as fertiUzers. Experience 

 has ever shown that the superior effects of sub- 

 stances on the surface of the ground arise from the 

 finer state in which the materials exist, and that 

 much of the benefits derived is owing to the atten- 

 tion that is bestowed on that point. 



Nature has produced bodies in various forms 

 and qualities, minute in bulk, diminutive, reduced 

 in size, concreted, and aggregate, and hard or soft, 

 fusible or vitreous, harsli or sweet, acid, acrid, or 

 corrosive. Some are more simple than others, or 

 they are formed of fewer elementary substances, 

 and are consequently capable of exercising a 

 chemical action on all substances in contact, for 

 all bodies of simple constituents have an aptitude 

 to enter into combinations and to effect decomposi- 

 tions, and the results will depend on the strength 

 of the respective actions. In making a change in 

 the nature of bodies, fire and water are the two 

 effective agents : the former banishes the existing 

 qualities, and confers new ones ; the latter, by its 

 insinuating force, disintegrates the mass and 

 sunders the particles, and brings the elements into 

 a fresh contact in an entirely different form. For 

 the purpose of being used as manures, most bodies 

 require to be altered in some way by means of 

 which the quality is brought nearer to the condition 

 which is known to yield the desired purpose. 

 Hardened or rocky substances are acted upon by 

 fire, and earthy matters are impregnated with 

 liquids. Other similar 'ays are used to prepare 

 the various matters th. are known to form the 

 useful substances. 



Marl. 



Of the fertihzing substances that are used in the 

 natural str.te, and for the application of which little 

 or no preparation has been found necessary, marl 

 holds a very prominent place. The name means 

 " marrow fat, or a preparation of the earth," and 

 by the ancients it was called " terrse adeps," and 

 was well known to them. It is a calcareous earth, 

 or a carbonate of lime with portions of other earths, 

 and assumes a fat, unctuous appearance after 

 crumbling or dissolution. Geology places it in the 

 tertiary formation, resting upon the gypsum, and 

 alternating with it. One bed is white and cal- 

 careous, and contains sihcified remains of trees, 

 plants, and shells; other beds are argillaceous and 

 of great thickness, and often contain balls of 

 celestine or sulphate of strontites. The uppermost 

 beds are thin, and contain large quantities of oysters : 

 marine shells abound in the beds that join with 

 sands and sandstones, and the last bed is of the 



