76 



AGRICULTURAL CHEMISTRY. 



the true elements of matter; many sub- disagreeable ; it is not respirable ; it sup- 

 stances formerly supposed to be simple, ports the combustion of all the common 

 have been lately decompounded, and the inflammable bodies except charcoal ; its 

 chemical arrangements of bodies must be specific gravity is to that of air as 24677 

 considered as a mere expression of facts, to 1000; it is soluble in about half its 

 the results of accurate statical experi- ' volume of water, and its solution in water 

 ments. i destroys vegetable colours: Many of the 



Vegetable substances in general are of a' metals (such as arsenic or copper) take fire 

 very compound nature, and consist of a | spontaneously when introduced into a jar 

 great number of elements, most of which j or bottle filled with gas. Chlorine may 



belong likewise to the other kingdoms of 

 nature, and are found in various forms. 



be procured by heating together a mixture 

 of 'spirits of salt or muriatic acid and 



Their more complicated arrangements manganese. The number representing the 

 are best understood after their simpler proportion in which the gas enters into 

 forms of combination have been examined. : combination is sixty-seven. 



The number of bodies which I consider 

 as at present undecomposed, are as w^s 

 stated in the introductory lecture, two 

 gasses that support combustion — seven in- 

 flammable bodies, and thirty eight metals. 



In most of the inorganic compounds, 

 the nature of which is well known, into 

 which these elements enter, they are com- 

 bined in definite proportions ; so that if 

 the elements be represented by numbers, 

 the proportions in which they combine are 

 expressed either by those numbers, or by 

 some simple multiples of them. 



I shall mention, in a few words, the 

 characteristic properties of the most im- 

 portant simple, substances, and the num- 

 bers representing the proportions in which 

 they combine in those cases, where they 

 have been accurately ascertained. 



3. Hydrogene, or inflammable air, is the 

 lightest known substance ; its specific 

 gravity is to that of air as 732 to 10,000. 

 It burns by the action of an inflamed taper 

 when in contact with the atmosphere. 

 The proportion in which it combines is 

 represented by unity, or 1. It is procured 

 by the action of diluted oil of vitriol or 

 hydro-sulphuric acid on filings of zinc or 

 iron. It is the substance employed for 

 filling air balloons. 



4. Azote is a gaseous substance not 

 capable of being condensed by any known 

 degree of cold: its specific gravity is to 

 that of common air as 9,516 to 10,000. It 

 does not enter into combustion under com- 

 mon circumstances, but may be made to 

 unite with oxygen by the agency of elec- 

 trical fire. It forms nearly four fifths of 



1. Oxygen forms about one-fifth of the the air of the atmosphere and may be pro- 

 air of our atmosphere. It is an elastic | cured by burning phosphorus in a confined 



fluid, at all known temperatures. Its 

 specific gravity is to that of air as 109G7 

 to 10,000. It supports combustion with 

 much more vividness than common air ; 

 so that if a small steel wire, or a watch 

 spring, having a bit of inflamed wood 

 attached to it, be introduced into a bottle 

 filled with the gas, it burns with great 

 splendour. It is respirable. 



It is very slightly soluble in water. The 

 number representing the proportion in 

 which it combines is fifteen. It may be 

 made by heating a mixture of the mineral 

 called manganese, and subphuric acid 

 together, in a proper vessel, or by heating 

 strongly red lead, or red precipitate of 

 mercury. 



2. Chlorine, or oxy muriatic gas, is like 

 oxygen, a permanent elastic fluid. Its 

 colour is yellowish green, its smell is very 



portion of air. The number representing 

 the proportion in which it combines is 

 2L6. 



5. Carbon is considered as the pure 

 matter of charcoal, and it may be produc- 

 ed, by passing spirits of wine through a 

 tube heated red. It has not yet been fused; 

 but rises in vapour at an intense heat. Its 

 specific gravity cannot be easily ascertain- 

 ed ; but thai of the diamond, which can- 

 not chemically be distinguished from pure 

 carbon is to that of water as 3500 to 1000. 

 Charcoal has the remarkable property of 

 absorbing several times its volume of dif- 

 ferent clastic fluids which are capable of 

 being expelled from it by heat. — The 

 number representing it is 11.4. 



6. Sulphur is the pure substance so 

 well known by that name ; its specific 

 gravity is to that of water as 1990 to 1000. 



