171 
years being the least common multiple of the two cycles, 
is mentioned by Herodotus as the apocatastatic period used 
by the Egyptians. 
Professor Kane read a paper “on the Theory of Ammo- 
niacal Compounds.” 
In this paper the author first noticed the various hypo- 
theses which had been from time to time proposed to explain 
the nature of the combinations formed by ammonia, and 
adverted particularly to the remarkable fact discovered by 
Mitscherlich, of the isomorphism of Nu; + Ho with K.o, and 
to the principle deduced by Dumas from the properties of 
oxamide, that NH, by losing an equivalent of hydrogen, 
formed a compound resembling very closely, and capable of 
replacing in combination, the simple bodies of the chlorine 
group. 
In the theory proposed by Dr. Kane, it is laid down as 
the fundamental proposition, that ammonia nH; must be 
represented as a compound of the body nu, and of hydrogen, 
that is, that ammonia, as gas, is amiduret of hydrogen. The 
hydrogen of this body, outside the radical, may be replaced 
by the various metals, or by radicals of organic origin, and 
hence the amide of potassium, of benzoyl, &c. These 
amides, resembling remarkably the chlorides, may unite with 
chlorides or oxides of the same, or of different metals, and’ 
hence the most general proposition, that in the great mass 
of the various ammoniacal combinations, their real nature 
assimilates them to complex metallic compounds, an amide of 
hydrogen, or of a metal, having united with a chloride, 
oxide, &c. of hydrogen, or of a metal. 
Thus sal ammoniac is considered in this theory as a com- 
pound of chloride of hydrogen with amide of hydrogen, and 
the oxide of hydrogen, united with amide of hydrogen, forms 
the basic element of the ordinary ammoniacal salts. In like 
manner, chloride of mercury, united with amide of mercury» 
R2 
