136 



FARMERS' REGISTER. 



[N6. 3 



to Ibrm a gas which we have called carbonic 

 acid. 



This receives the latter part of its name from its 

 similarity in properties to an extensive class of 

 compound bodies, known by the name of The 

 Jlc'ids. The greater part of these, like carbonic 

 acid, are combinations of inflammable bodies with 

 oxygen. The most important of these, in refer- 

 ence to our present object, are the sulphuric and 

 phosphoric acids: named li-om the two substances 

 (sulphur and phosphorus) which are their bases. 

 Muriatic acid may also be mentioned here, al- 

 though its composition is of a different character. 

 Oxygen unites with other bodies to form a class 

 of compounds known under the name of oxides. 



The acids unite with earths, alkalis, and me- 

 tallic oxides, to form a class of compounds known 

 under the general name of salts. These are 

 named from the two substances which enter into 

 their composition: thus, the salt Ibrmed of sul- 

 phuric acid and the earth lime, is called sulphate 

 of lime. The substances which unite with acids 

 to form salts, are called the bases of the respective 

 ealts. 



Of these bases, the alkalis and earths are the 

 most important. Of the alkalis, it is only neces- 

 sary to know the names of two, namely potassa 

 and soda, and to be aware that their distinctive 

 properties, are — to possess an acrid taste, a caus- 

 tic operation, to render oils capable of mixing 

 with water, and to neutralize the properties of 

 acids. 



The earth which chemists call by the name 

 of silex or silica, is found almost pure in flint and 

 rock crystal; it is also almost pure in sharp color- 

 less sands, and is by far the larger juirt of sands of 

 every description. 80 far as the tiirmer need 

 know its properties, it is hard, rough to the touch, 

 has no attraction for water, which it permits to fil- 

 ter through, or evaporate from it, with the greatest 

 ease. It is capable of uniting Avith the other 

 earths in compounds which are called silicates, and 

 is the only earth which enters into the formation of 

 fioils uncombined with the others or with other ele- 

 ments. I 



The earth which chemists call by the name of 

 alumina, is so named because it is obtained by 

 them in a pure Ibrm fiom the well-known salt call- 

 ed alum, of which it is tlxe basis. Its most marked 

 characteristic is plasticity: (hat is to say, it may 

 be formed into a paste with water, will then easi- 

 ly receive any form which may be given it, and 

 retain that form unaltered, even by violent heat. 

 It never exists in soils unmixed, but in intimate 

 association, or more probably chemical combina- 

 tion with silica, it is the well-known substance call- 

 ed clay, or argillaceous earth. White clayrj are this 

 combination nearly pure, and colored clays oltcn 

 contain it wiili no other addition than metallic co- 

 loring matter. Clay retains the ])lasiic property 

 of alumina; it thereibre causes soils to be reten- 

 tive of moisture; and, when they dry, makes them 

 form tough clods or crusts, similar in character to 

 sun-dried brick. 



Soils which contain claj^ are oflen also mixed 

 with sand, or with an excess of silica in grains, 

 which does not enter into composition of the clay. 

 Such a soil is less liable to Ibrm a tough crust than 

 a pure clay, but it will refjuire a very large pro- 

 portion of sand to destroy this property alto- 

 gether. 



Clay mixed wilh sandy soils renders them more 

 retentive of moisture. Sand and clay have there- 

 ibre been used as manures fbr each other; but it 

 may reasonably be doubted whether all the ad- 

 vantage that has been anticipated by some ironi 

 this process, can be realized, as such a mixture 

 will be merely mechanical. 



Loamy soils are generally said to be mixtures 

 of sand and clay; they undoubtedly usually con- 

 tain both these earths, and even sometimes a large 

 excess of sand. But we shall give reasons lor 

 believing that loams owe their peculiar value to a 

 combination of clay with another substance, by 

 which a change is produced in its chemical char- 

 acters. 



Lime is familarly known to farmers by the same 

 name that is generally used by chemists. It is 

 obtained by the aid of heat from rocks which go 

 by the name of limestones. These are combina- 

 tions of lime with carbonic acid, which is fixed in 

 them by chemical attraction, but which, when 

 driven off by heat, takes the same form as the air 

 of the atmosphere, or becomes a gas. This gas 

 from this circumstance has been called fixed air, 

 by which name it is often known when causing 

 the sparkling and li'oth of cider and beer. The 

 principal part of limestone is therefore called by 

 chemhts carbonate (]f lime. Carbonate of lime is 

 also found in shells, both of those of living ani- 

 mals, and those which exist in the ground in a fos- 

 sil state. In the fbrmer it is mixed with animal 

 matter, which is more or less separated fi'om the 

 latter according to the time which has elapsed since 

 the death of the shell fish. 



Marl, in the sense in which the term is used by 

 chemists, is a mixture of clay with carbonate of 

 lime. The English writers on agriculture have 

 not observed this distinction, and the term is some- 

 times a|)p!ied by them to a decomposed chalk, 

 which may contain little or no clay; and some- 

 times to clay which contains no carbonate of lime. 

 In fact, the name is frequently applied by them to 

 any earthy matter found below the vegetable soil, 

 which is capable of increasing its fertility. From 

 this misapprehension, the substances whch go by 

 the name of marl in New Jersey, Maryland, and 

 Virginia, do not correspond with the chemical de- 

 finition, but are generally beds of fossil shells, 

 mixed in various proportions with earthy and sa- 

 line matters of various kinds. 



Lime is a substance very different in its charac- 

 ters fi'om the two earths of which we have pre- 

 viously spoken. When prepared by heat from 

 any of the original fbrms of its carbonate, it re- 

 tains their shape unaltered, but may have its color 

 changed, and always loses considerably in weight. 

 It is now acrid, caustic, and corrosive, and has 

 some properties in common with potash, which 

 are therefore alkaline. Of these the most im- 

 portant is, that it unites vvtlh acids to form com- 

 pounds included in the general class of salts. Of 

 the salts of lime which are important to (he farm- 

 er, the three principal are — the carbonate, wU'n-h, 

 as we have stated, is found in limestone, chalk, 

 shells, and marl; the sulphate, in which lime is 

 combined with sulphuric acid, and which, in com- 

 bination with waler,is the substance so well known 

 to our liu-iners under the name of plaster of Paris, 

 or less familiarly by that of gypsum; \he phos- 

 phate, which constitutes a large part of the bones 

 of animals. 



