0X1 



oxo 



from the action of oxygen; but in gold 

 and platina, no perceptible change is ob- 

 served, for whatever length of time they 

 are exposed to the atmosphere. This 

 oxydation, and the quantity of oxygen 

 absorbed, is proportionable to the tempe- 

 rature. There are, however, many metals 

 which combine with a determinate pro- 

 portion of oxygen at certain tempera- 

 tures, and from this may be estimated the 

 quantity of oxydation from the degree of 

 beat which has been applied- The rapidi- 

 ty of the oxydation is almost always in- 

 creased by the elevation of temperature. 

 In this way actual combustion or inflam- 

 mation is produced. Thus filings of 

 metals thrown upon a body in a state of 

 ignition, give out brilliant sparks ; and 

 steel, struck upon a flint, burns with a 

 vivid flame in the air, in consequence of 

 the great heat which is communicated to 

 it by percussion. Metallic substances 

 combine with very different proportions 

 of oxygen ; and this quantity varies ac- 

 cording to the manner in which the pro- 

 cess has been conducted, or the tempe- 

 rature to which the metal has been ex- 

 posed. 



In these different, states and conditions 

 of oxydation different phenomena are ex- 

 hibited. Sometimes the metal becomes 

 red hot, and is inflamed ; sometimes the 

 oxygen takes place without fusion, or 

 does not combine with oxygen till after 

 it has been melted; sometimes it is co- 

 vered with a brittle crust, or with a sub- 

 stance in the form of powder. At other 

 times a pelicle, exhibiting different co- 

 lours, forms on the surface : but, in all 

 cases, the metal is tarnished, loses its bril- 

 liancy and its colour, and assumes another, 

 which announces the change that has taken 

 place. Another difference which takes 

 place among metals, is the different de- 

 grees of force with which the oxygen ad- 

 heres to the metal. The knowledge of 

 this, and the different degrees of affinity 

 between oxygen and metallic substances, 

 is of great importance in many operations 

 and chemical results. During the fixa- 

 tion of oxygen in metallic substances, it 

 is absorbed by some in its solid state, and 

 gives out a great deal of caloric. In 

 others it is combined, without giving out 

 the same quantity. This proportion of 

 caloric given out corresponds to the 

 facility with which oxides part with their 

 oxygen, or are reduced to the metallic 

 state. Those which have combined with 

 oxygen, with the greater proportion of 

 caloric, are most easily reduced ; but 

 those, on the contrary, in whi^h the oxy- 



gen has been deprived of its caloric, are 

 reduced to the metallic state by a great 

 addition of caloric, and the greatest num- 

 ber of oxides require the addition of sub- 

 stances, whose affinity for oxygen is 

 greater than that of the metal. Metallic 

 oxides are extremely different in different 

 metals, and even in the same metal, ac- 

 cording to the proportion of oxygen. 

 They are, however, possessed of some 

 common properties. They are all in the 

 form of powder or earthy substance, or 

 so brittle as to be easily reduced to this 

 state They exhibit every shade of co- 

 lour, from pure white to brown and deep 

 red, and they are heavier than the metals 

 from which they have been obtained. 

 Some oxides are revived, as it is called, 

 or are reduced to the metallic state, 

 merely by being in contact with light or 

 caloric. Some require the addition of a 

 combustible substance and a high tem- 

 perature ; while others have so strong an 

 affinity for oxygen, that they cannot be 

 deprived of it by the strongest beat, but 

 become fusible in the fire, and afford a 

 glassy matter more or less coloured, and 

 even serve as a flux to the earths. Some 

 oxides are volatile, but the greatest num- 

 ber are fixed. Some have an acrid and 

 caustic taste, are more or less soluble in 

 in water, and even possess an acid quali- 

 ty ; others are insoluble and insipid. 



OXOPHYLLUM, in botany, a genus of 

 the Monadelphia Pentandria class and 

 order. Natural order of Trihilatse. Me- 

 liae, Jussieu. Essential character ; one- 

 styled ; calyx five toothed; petals five, 

 long ; filaments sheathing the style, five- 

 toothed at top ; teeth antheriferous ; stig- 

 ma one ; capsule five-celled. There is but 

 one species, viz. O. foetidum ; this is a 

 shrub about ten feet in height, and nearly 

 six inches in diameter ; the bark is green 

 and smooth, the wood white, tender, and 

 fragile ; the branches twiggy, garnished 

 with alternate leaves, each leaf digitated, 

 having three large lobes growing on a 

 foot-stalk of five or six inches in length ; 

 each lobe is divided by a longitudinal 

 nerve, which is prominent beneath; the 

 flowers spring from the bottoms of the 

 leaves, at the extremity of the twigs and 

 branches; their common foot-stalk is 

 about a foot in height, dividing at its sum- 

 mit into several smaller ones, on each of 

 which are placed alternate sessile flow- 

 ers ; the corolla is white,each petal being 

 an inch long, and, as it were, glued to 

 each other, longitudinally, by their bor- 

 ders, so as to form a kind of tubular 

 figure, the upper part spreading ; these 





