A I R 



AIR 



Tlicy may likewise be raised by cutting some 

 ■of the smaller roots, and theji turning them up. 



It is a.tree that grows very fast in this climate, 

 and from iis bdiig handsome, and rising to a 

 considerable height, is proper for omamenta] 

 plantations, or large clumps ui pleasure grounds. 

 If the bark be wounded, a resinous substance 

 issues from it, which sf)on hardens. Its wood 

 is hard, heavy, glossy like satin, arul suscepti- 

 ble of taking a very fine polish. It may of course 

 be made use of for various purposes. 



AIR, when considered in respect to vegeta- 

 tion, is the thin medium which surrounds, and 

 becomes intermixed with, the particles of the 

 soil ; and in this way, as well as by being ab- 

 sorbed and taken up by the organs of plants, 

 ■contributes in a great measure to tiieir health, 

 grov.-th, and support. 



Jt is ^substance possessed of weight or gravity, 

 and capable of being compressed ; but not con- 

 (icnsible in tlie heat of the atmosphere without 

 combination. Without the aid of this medium, 

 vegetables could not live, file be maintained, or 

 heat sjcnerated. But though the atmosphere be 

 the vast bboratory in w hich nature performs va- 

 rious operations, solutions, precipitations, and 

 •combinations, and the grand receiver in which 

 all the attenuated and volatilized productions of 

 terrestrialbodies are lodged, mingled, agitat^, 

 combined, and separated ; still the air is the 

 same in respect to its qualities, being decidedly 

 ■characterized by the two properties of support- 

 jno" respiration and combustion. This is suffi- 

 ciently evident from combustible bodies not be- 

 ino- burnt without the contact of atmospheric 

 air, as in vacuo this process does not take place. 

 From respiration and combustion not continuing 

 beyond a certain length of time in a given qu;m- 

 tity of atmospheric air, it is likewise obvious 

 that only a part of the air that surrounds the 

 earth is proper for the support of either animal 

 or vegetable life, or combustion, the other being 

 improper for these purposes. Hence it is evident 

 that atmospheric air is a compound of two dift'e- 

 rent sorts of air : the one supporting respiration 

 and combustion, and on that accoimt denomi- 

 nated vital air, pure air, or oxygen ; the other 

 injurious in these respects, but necessary in a 

 certain proportion, in order to modify the too 

 powerful action of vital air, or oxygen, in the 

 respiration of animals: this is termed, from its 

 properties, azote or phlogi^ficated air. One hun- 

 dred parts of common or atmospheric air contain 

 twenty-seven of the oxygenous or pure air, and 

 seventy-three of the azotic oi nitrogen air, as has 

 been shown by the late experiments in chemistr}'. 



Besides these principles, the conmion or at- 

 mospheric air also contains a proportion oi fixed 



air, OT what is now termed carbonic acid gas, 

 from carbonaceous matter, or charcoal, forming 

 one of its constituent principles. The vital air, 

 or oxvgen, by combining with oiher bodies, 

 produces dificrcnt new compounds that may be 

 of great utilitv in the vegetation of plants. 



Loi^g before the discoveries in modern che- 

 mistrv had ascertained the constituent principles 

 of common air, it had been remarked to be a 

 principal agent in the vegetation of plants by 

 Mr. liay, m the Philosophical Transactions, 

 who fouiid that lettuce seed, which was sown in 

 the glass receiver of the air-pump, exhausted 

 and "cleared from all air, grew not at all in 

 eight days time : whereas some of the same seed, 

 which was sown ait the same time in the open 

 air, had risen to the height of an inch and a half 

 in that time ; but on the air being let into the 

 exhausted receiver the seed grew up to the height 

 of two or three inches in the space of one week. 

 The insrcnions experiments that have been lately 

 made bv Mr. Gough, and detailed in the Trans- 

 actions of the Manchester Philosophical Society, 

 have still more clearly demonstrated, that the 

 vegetation of most sorts of seeds depends in a 

 great measure upon the presence of the oxyge- 

 nous principle of the air. And another proof 

 of the utility of air in vegetation is met with in 

 the Sediun, which pushes out roots without earth 

 or water, and lives several months. Some sorts 

 of Aloes, if hung up in a room entirely secured 

 from frosts, will remain fresh for some years, 

 though they sensibly lose in their weight. 



Air also operates witliin the earth, and, from 

 the changes which it imdergoes, and the new 

 combinations that are formed in consequence of 

 them, contributes greatly to promote the growth 

 of plants. 



Thus it has been observed by the author of 

 the Philosophy of Gardening, that as most 

 earths contain carbon, and other inflammable 

 materials that are capable of uniting with oxygen, 

 and by that means aflbrd carbonic or other . 

 acids; as well as water which, by its decompo- 

 sition when in contact with confined air, forms 

 ammonia, or volatile alkali, by its hydrogen 

 combining with azote, and nitre by the con- 

 junction of its abundant oxygen wuh another 

 portion of the abundant azote or nitrogen of the 

 atmospheric air, there is good ground to conclude 

 that the great utility of turning over the earth by 

 tlie spade, may arise from the production of such 

 eftccts, by the confining of the oxgyen, as well 

 as the azote or nitrogen, of the air in the pores 

 among the particles of the mould : and as these 

 effects must be produced more extensively and 

 more readily, in proportion, as the particles of 

 the earth are more perfectly broken down and 



