94 



AGRICULTURAL CHEMISTRY. 



feet over with pounded chalk will be ef-|gen, and its constitution is consequently 

 factual to prevent it; the rubbing; is useful, 75 potassium, 15 oxygen 



and the chalk keeps the feet warm by be- 

 ing a bad conductor of heat. 



The invisible causes of indolent dispo- 

 sitions are also various. The first of the 

 spontaneous is a diseased increase of 

 growth. 



2nd. Interstitial swelling. 



.3d. New formed substance. 



This division, according to the mode of 

 increase, is into three kinds, viz. increase 

 of natural parts, the interstitial, and the 

 tumour. All these are liable to happen in 

 every part of the body. These increases 

 are either known by the sight or by the 

 feel. 



AGRICULTURAL CHEMISTRY. 



(Continued from p. 78.) 



Combustion in fact, in common cases, 

 is the ])rocess of the solution of a body in 

 oxygen, as happens when sulphur or char- 

 coal is burnt; or the fixation of oxygen by 

 the combustible body in a solid form, 

 which takes place when most metals are 

 burnt, or when phosphorus inflames, or 

 the production of a fluid from both bodies, 

 as when hydrogen and oxygen unite to 

 form water. 



When considerable quantities of oxy- 

 gen or of chlorine unite to metals, or in- 

 flammable bodies, they often produce 

 acids; thus sulphurous, phosphoric, and 

 boracic acids, are formed by a union of 

 considerable quantities of oxygen with 

 sulphur, phosphorus, and boron: and mu- 

 riatic acid gas is formed by the union of 

 chlorine and hydrogen. 



When smaller quantities of oxygen or 

 chlorine unite with inflammable bodies or 

 metals, they form substances not acid, and 

 more or less soluble in water; and the me- 

 tallic oxides, the fixed alkalies, and the 

 earths, all bodies connected by analogies, 

 are produced by the union of metals with 

 oxygen. 



The composition of any compounds, 

 the nature of which is well known, may 

 be easily learned from the numbers repre- 

 senting their elements; all that is necessa- 

 ry is to know how many proportions enter 

 into union. Thus potassa, or the pure 

 caustic vegetable alkali, consists of one 

 proportion of potassium and one of oxy- 



Carbonic acid is composed of two pro- 

 portions of oxygen, 30, and one of carbon, 

 11,4. 



Again, lime consists of one proportion 

 of calcium and one of oxygen, and it is 

 composed of 40 of calcium and 15 of oxy- 

 gen. 



And Carbonate of lime, or pure chalk, 

 consists of one proportion of carbonic acid, 

 41.4, and one of lime, 55. 



Water consists of two proportions of 

 hydrogen, 2, and one of oxygen, 15; and 

 when water unites to other bodies in defi- 

 nite proportions, the quantity is 17, or 

 some multiple of 17, i. e. 34, or 51, or 

 68, &c. 



Soda, or the mineral alkali, contains 

 two proportions of oxygen to one of so- 

 dium. 



Jiinrnonia, or the volatile alkali, is 

 composed of six proportions of hydrogen 

 and one of azote. 



Amongst the earths, Silica, or the earth 

 of flints, probably consists of two propor- 

 tions of oxygen to one of silicum; and 

 Magnesia, Slrontia, Baryta or Bary- 

 tes, Mxnnina, Zircona, Glusina, and 

 Ittria, of one proportion of metal and one 

 of oxygen. 



The metallic oxides in general consist 

 of the metals united to from one to four 

 proportions of oxygen; and there are, in 

 some cases, many different oxides of the 

 same metal; thus there are three oxides of 

 lead; the yellow oxide or massicot, con- 

 tains two proportions of oxygen; the red 

 oxide or minium, three; and thejot^ee co^ 

 loured oxide, four proportions. 



Again, there are two oxides of copper ^ 

 the black and the orange; the black con- 

 tains two proportions of oxygen, the 

 orange one. 



For pursuing such experiments on the 

 composition of bodies as are connected 

 with agricultural chemistry, a few only of 

 the undecompounded substances are ne- 

 cessary; and amongst the compounded bo- 

 dies, the common acids, the alkalies, the 

 earths, are the most essential substances. 

 The elements found in vegetables, as has 

 been stated in the introductory lecture, 

 are very few. Oxygen, hydrogen, and 

 carbon, constitute the greatest part of their 



