16 Recent Developments of Chemical Science. [January, 
simple bodies thus frequently met with uncombined are — 
Copper, silver, gold, mercury, arsenic, antimony, bismuth, 
sulphur, selenium, and tellurium ; lead and tin occasionally 
occur naturally in the metallic state. Gallium, indium, 
thallium, and cadmium are of such rare occurrence that we 
can scarcely venture to state whether they occur in the free 
condition or not. Among the bodies which belong to the 
uneven series, and still are not met with in the free state, 
only chlorine, bromine, iodine, fluorine, zinc, and phosphorus 
are noteworthy exceptions, whilst sodium, magnesium, 
aluminium, and silicon are explained by Mendelejeff ’s prin- 
ciple b. As regards the exceptions among the even series, 
carbon, nitrogen, and oxygen come under b, and the group 
VIII. under c. 
3. As concerns the occurrence of the elements in Nature 
in a combined condition, Prof. Carnelley, leaving the ele- 
ments chlorine, bromine, iodine, and fluorine, and the group 
VIII., for future consideration, proposes that — 
The elements belonging to the odd series generally occur 
in Nature as sulphides or double sulphides (or selenides, 
tellurides, and arsenides), — i.e., in combination with a nega- 
tive element belonging to an odd series, — and only in very 
rare cases as oxides. Elements belonging to the even series 
are generally found as oxides or double oxides (with the 
formation of silicates, carbonates, sulphates, aluminates, 
&c.), — that is to say, with a negative element belonging to 
an even series, — and in two instances only as sulphides. 
Thus the following elements belonging to the even series 
occur as oxides or double oxides : — 
Commonly : Lithium (in lepidolite, &c.), potassium (in 
saltpetre and felspar), rubidium, caesium, beryllium, calcium, 
strontium, barium, boron, scandium, yttrium, lanthanum, 
ytterbium, carbon, titanium, zirconium, cerium, thorium, 
vanadium, niobium, didymium, tantalum, oxygen, chromium, 
tungsten, manganese. 
Frequently: Nitrogen (in saltpetre), molybdenum. 
Rarely or never : None. 
As sulphides : — 
Commonly : Molybdenum. 
Very rarely : Manganese, also oxygen as sulphurous acid 
in volcanic gases. 
Elements belonging to uneven series occur as sulphides 
(selenides or tellurides) : — 
Commonly: Copper, silver, zinc, cadmium, mercury, 
