naturally confined to those oxides which easily part with their oxygen—as, for instance, copper oxide—whilst the oxides of magnesium or potassium are not reduced. Metallic iron itself is capable of reducing carbonic anhydride to carbonic oxide, just as it liberates the hydrogen from water. Copper, which does not decompose water, does not decompose carbonic oxide. If a platinum wire heated to 300°, or spongy platinum at the ordinary temperature, be plunged into a mixture of carbonic oxide and oxygen, or of hydrogen and oxygen, the mixture explodes. These reactions are very similar to those peculiar to hydrogen. The following important distinction, however, exists between them—namely: the molecule of hydrogen is composed of H2, a group of elements divisible into two like parts, whilst, as the molecule of carbonic oxide, CO, contains unlike atoms of carbon and oxygen, in none of its reactions of combination can it give two molecules of matter containing its elements. This is particularly noticeable in the action of chlorine on hydrogen and on carbonic oxide respectively; with the former chlorine forms hydrogen chloride, and with the latter it produces the so-called carbonyl chloride, COCl2: that is to say, the molecule of hydrogen, H2, under the action of chlorine divides, forming two molecules of hydrochloric acid, whilst the molecule of carbonic oxide enters in its entirety into the molecule of carbonyl chloride. This characterises the so-called diatomic or bivalent reactions of radicles or residues. H is a monatomic residue or radicle, like K, Cl, and others, whilst carbonic oxide, CO, is an indivisible (undecomposable) bivalent radicle, equivalent to H2 and not to H, and therefore combining with X2 and interchangeable with H2. This distinction is evident from the annexed comparison:
| HH, hydrogen. | CO, carbonic oxide. |
|---|---|
| HCl, hydrochloric acid. | COCl 2 , carbonyl chloride. |
| HKO, potash. | CO(KO) 2 , potassium carbonate. |
| HNH 2 , ammonia. | CO(NH 2 ) 2 , urea. |
| HCH 3 , methane. | CO(CH 3 ) 2 , acetone. |
| HHO, water. | CO(HO) 2 , carbonic acid. |
Such monatomic (univalent) residues, X, as H, Cl, Na, NO 2 , NH 4 , CH 3 , CO 2 H (carboxyl), OH, and others, in accordance with the law of substitution, combine together, forming compounds, XX'; and with oxygen, or in general with diatomic (bivalent) residues, Y—for instance, O, CO, CH 2 , S, Ca, &c. forming compounds