No, 4. 



Explanation of Terms. 



59 



coal, when burning, and forms carbonic acid 

 gas, already described ; and hence we see how 

 the carbonic acid gas, which sometimes proves 

 fatal in close shut bed-chambers, heated with 

 burning charcoal, is produced. The oxygen in 

 the atmosphere unites with the charcoal or car- 

 bon in burning, and thus produces this gas so 

 deleterious to life when breathed without a due 

 proportion of atmospheric air mixed with it. 



These four elementary substances, Oxygen, 

 Hydrogen, Azote and Carbon, possess a very 

 wonderful agency in nature, and every one who 

 has any wish to look beyond the mere surface 

 of things cannot but be gratified in knowing 

 more about them. We shall have further oc- 

 casion to speak of these substances in the Cabi- 

 net ; it is important therefore that the character 

 and distinguishing properties of each should be 

 well understood. These are given in the follow- 

 ing concise deiinitions. which are not to be for- 

 gotten; viz., 



49. Oxygen — is one of the constituent 

 principles of water ; it is called vital or re- 

 spirable air, and is essential both to the sup- 

 port of life and combustion. 



This substance performs an important part in 

 most of the changes which take place in the 

 mineral, vegetable, and animal kingdoms. 



50. Hydrogen — is one of the constituent 

 principles of water ; it is very inflammable, 

 and was formerly called inflammable air. It 

 is the lightest of all ponderable substances. 



This is the substance generally used in filling 

 air-balloons. It is readily obtained by the de- 

 composition of water. Vegetables and animals 

 also in a state of decay and putrefaction afford 

 it, and it is evolved from various mines and vol- 

 canoes. 



51. Azote — is that part of atmospheric air 

 which is incapable of supporting life or com- 

 bustion. 



All combustible substances burn violently in 

 pure oxygen gas, and if it was not diluted in 

 the atmosphere by a large portion of azote, it 

 would be impossible to extinguish any consi- 

 derable fire when once lighted up, and some- 

 thing like the general conflagration of the world 

 would immediately commence. 



Azote exists abundantly in nature, forming 

 the greater part of the atmosphere, and is one 

 of the principle ingredients in animal substances 



52. Carbon — is the pure part of charcoal. 



Carbon forms a large proportion of all vege- 

 tables; it exists also in animals, but its quantity 

 is small. 



53. Carbonic Acid — is a combination of 

 carbon and oxygen, in the proportions of 18 

 parts carbon to 82 parts ox'ygen. 



An account of this substance has already 

 been given under the article " Acids," It may 

 here be added, that the sources of this acid are 

 immense. It exists in the atmosphere; it is 

 found in abundance in many mineral waters, as 

 ot Ballslon and Saratoga in the state of New 



York ; it is produced by the combustion of wood 

 and charcoal, by the fermentation of liquors, 

 and by the decomposition or putrefaction of 

 vegetable substances; but the largest store of it 

 is that enormous quantity solidified or rendered 

 solid in all the immense beds of chalk and lime- 

 stone with which every part of the globe 

 abounds. 



Of limestone 45 parts in every 100 are com- 

 puted to be carbonic acid. 



As before observed, when uncombined with 

 any other substance, it always exists in the state 

 of gas. It is heavier than atmospheric air. If 

 this gas be poured from a wide-mouthed jar 

 upon a lighted candle, it will be as effectually ex- 

 tinguished as by water. 



54, Effervescence — is a sudden disengage- 

 ment of gas taking place within a liquid and 

 separating from it with a hissing noise. 



We have an example of this, as before ob- 

 served, by dropping a little pearl ash into cider. 

 The carbonic acid is disengaged and rises in the 

 form of gas, producing much foam, with a hiss- 

 ing noise. 



5,5. Chemical Affinity — is a term used to 

 signify the attraction or tendency there is 

 between the particles of certain substances, 

 of different natures, to unite, thereby form- 

 ing a tliird substance possessing properties 

 altogether difierent from those of either of 

 the two substances of which it is composed. 



Thus, potash and oil have a tendency to 

 unite, thereby forming soap, which is a third 

 substance very different either from the oil or 

 the potash of which it is composed. 



Those substances which are capable of unit- 

 ing in this manner, are said to have an affinity 

 for each other, as oil and potash ; but oil will 

 not unite with water, and therefore those sub- 

 stances which do not form a chemical union, 

 are said to have no affinity, 



56. The Primitive Earths — are four ; viz. 

 clay, sand, lime and magnesia. 



These are the only earths which enter into 

 the composition of soil ; they enter also in very 

 minute portions into the organization of plants. 



Sand and clay are by far the most abundant; 

 lime is required but in small proportions ; every 

 soil however is defective without it. Magnesia 

 is found but in few soils; its place is well sup- 

 plied by lime ; its entire absence therefore is not 

 considered any defect. 



57. Clay — in agricultural publications, is 

 called alumina, alumine, aluminous, or argil- 

 laceous earth. 



•' The term clay should not be given to a soil 

 which contains less than one sixth part of alum- 

 inous earth." 



58. Sand — is called silex, silica, silicious 

 earth, or earth of flints. 



" Tlie epithet sandy is not properly applied to 

 any soil, that does not contain at least seven- 

 eighth parts of sand ; and sandy soils arc to be 



