ORGANIC MANURES. 51 



poured from one open vessel into another, without material 

 loss. It is this which gives to artificial soda water and to 

 mineral springs (as the Saratoga) their sparkling appearance 

 and aci'l flavor. It abounds in certain caves, sunken pits, 

 and wells, which destroy animal life, not from any intrinsic 

 poisonous qualities, but from its excluding oxygen, which is 

 essential to respiration. And it is from the same cause, 

 that death ensues to such as are confined in a close room 

 where charcoal is burnt. 



This acid is an active and important agent in the inces- 

 <ant changes of nature. It is everywhere formed in vast 

 quantitics t by subterranean fires and volcanoes. Though 

 heavier than atmospheric air, it mingles with it and is car- 

 ried as high as examinations have yet been made, consti- 

 tuting in bulk, about one part in 1000 of the atmosphere, 

 and something more than this in weight. Gay Lussac 

 ascended in a balloon '21,735 feet, and there filled a bottle 

 with air, which analysis showed to be identical in composi- 

 tion with that on the surface of the earth. Carbon is one of 

 the great principles of vegetation, and it is only as carbonic 

 acid, that it is absorbed by the roots, leaves and stems of 

 vegetables, and by them is condensed and retained as solid 

 matter. 



OXYGEN, hydrogen and nitrogen, when uncombiued with 

 other substances, exist only as gases. The first makes up 

 nearly one half of all the substances of the globe; and with 

 the exception of chlorine and iodine, it constilutes a large 

 part of every material in the ash of plants. It forms rather 

 over 21 per cent, by measure, and 23 by weight of the whole 

 atmosphere ; and about 8 parts out of nine by weight of 

 water, hydrogen making up the remainder. It is absorbed 

 and changed into new products by the respiration of ani- 

 mals, and it is an essential agent in combustion. Oxides 

 are composed of it in union with the metals, alkalies, &c. ; 

 and most of the acids, as when combined with other substan- 

 ces, nitrogen, sulphur and phosphorus. Its presence indeed, 

 is almost universal and the agency which it exerts in vegetn- 

 ble nutrition, is among the most varied and intricate mani- 

 fested in vegetable life. 



HYDROGEN is the lightest of all the gases. It is but l-14th 

 the weight of the atmosphere, and l-16th the weight of oxy- 

 gen ; and from its great levity, it is used for fill ing balloons, 

 ft burns with a light flame when brought into contact with 



