Nitrogen gas may be regarded in the light of a diluent to the oxygen. In its pure state it is only characterised by its negative properties. It will not burn, or act as a supporter of combustion. Animals speedily perish if confined in it; but they die rather through the absence of oxygen than from any poisonous property of this gas. Yet, in combination, we find nitrogen exhibiting powers of a most energetic character. In addition to the fulminating compounds and the explosive substances already named, which are among the most remarkable instances of unstable affinity with which we are acquainted, we have also the well-known pungent body, ammonia. From the analogous nature of this volatile compound, and the fixed alkalies soda and potash, it was inferred that it must, like them, be an oxide of a metallic base. Davy exposed ammonia to the action of potassium, and to the influence of the voltaic arc produced from 2,000 double plates, without at all changing its character. From its slight tendency to combination, and from its being found abundantly in the organs of animals feeding on substances that do not contain it, it is, however, probably a compound body. A phenomenon of an obscure and mysterious character is presented in the formation of the “ammoniacal amalgam,” as it is called. Mercury, being mixed with an ammoniacal salt, is exposed to powerful galvanic action; and a compound, maintaining its metallic appearance, but of considerable lightness and very porous, presents itself.[229] This preparation has been carefully examined by Davy, Berzelius, and others. It is always resolved into ammonia and mercury; and, although the latter chemist is strongly inclined to regard it as affording evidence of the compound nature of nitrogen,--and he has, indeed, proposed the name _nitricum_ for its hypothetical base,--yet, to the present time, we have no satisfactory explanation of this apparent metallization of ammonia.