146 TENTH ANNUAL REPORT OF 



air in tliin laminte, as by causing it to trickle slowly tlirougli a per- 

 forated cask filled with wood shavings, a few hours will he found suf- 

 ficient to effect perfectly its oxydatiou. 



The tendency of bodies to unite with oxygen is greatly increased 

 if the product of their union be capable of acting as a base by the 

 presence of an acid ; or if it be capable of acting as an acid, by the 

 presence of a base. Thus iron, copper, lead, and tin, corrode much 

 faster in acidulated than in pure water. Even the small quantity of 

 carbonic acid always present in rain and spring water materially 

 facilitates the oxydation of the metals immersed in them. There is 

 superadded to the affinity of the metals for the oxygen that of their 

 oxides for the acid ; and if the resultant salt chance to be soluble, 

 their surface is kept constantly fresh for the corrosive action. The 

 oxydation of lead by water becomes a source of contamination only 

 when there is an acid present to unite with the oxide formed, and 

 render it soluble. The wasting of the copper sheathing of vessels by 

 sea-water is due not merely to the oxygen, but to the contained salts 

 with which the copper, either as an oxide or as a carbonate, enters 

 into reactions. 



The arts avail themselves of this principle in the manufacture of 

 salts. The sulphate of copper is formed by the repeated immersion of 

 sheets of the metal in sulphuric acid so far diluted with water as to 

 give it the power of absorbing oxygen. The same metal exposed to 

 the combined influence of air, water, and acetic acid, passes into an 

 acetate. Lead, under like circumstances, is converted into an acetate ; 

 or, if the proper conditions be secured, the acetic acid as well as the 

 lead suffers oxydation, and a carbonate is produced. It is in this way 

 that white lead is ordinarily manufactured. 



If the body uniting with oxygen form an acid, the combination will 

 be facilitated by the presence of a base. This fact explains why the 

 decay of organic substances is hastened by lime, potash, or soda. 

 There is superadded to their afiinity for oxygen, the affinity of these 

 powerful bases for the products of their oxydation. Even gold and 

 platinum, if heated in the air, in contact with either of the alkalies, 

 suffer oxydation. Nitrogen, though ordinarily manifesting so little 

 affinity for oxygen, spontaneously unites with it when the two gases 

 are dissolved in water and brought together in the presence of an 

 alkali or an alkaline earth. It is probably in this manner that the 

 nitrates, natural as well as artificial, are for the most part formed. 



As oxygen and water, the medium through which it is presented, 

 are both universally diffused, bodies have a constant tendency to unite 

 with it, and if left to themselves, do in fact, sooner or later, pass to 

 the state of oxides. This is their natural or statical condition ; and 

 although they may be temporarily reclaimed, they cannot be pre- 

 vented from ultimately reverting to it. Metals find their way back 

 to the stat;e of ores from which they have been brought. The bodies 

 of animals and plants, so long as life continues, are, indeed, exempt 

 from the attacks of oxygen ; but no sooner does life cease than they 

 are laid hold of by this universal, omnipresent element, and fast con- 

 verted into the substances from which they were formed. The wort 

 of their demolition is assisted by innumerable insects, which, pursuing 



