It is a regular constituent of the atmosphere, and is found in many spring waters and in volcanic gases; it also occurs in the uncombined condition at the Grotto del Cane (Naples) and in the Poison Valley (Java).
Cadmium does not occur naturally in the uncombined condition, and only one mineral is known which contains it in any appreciable quantity, namely, greenockite, or cadmium sulphide, found at Greenock and at Bishopton in Scotland, and in Bohemia and Pennsylvania.
The metals comprising this group are never found in the uncombined condition, but occur most often in the form of carbonates and sulphates; they form oxides of the type RO, and in the case of calcium, strontium and barium, of the type R02.
In curd soaps, however, which form the basis of most household soap, the uncombined alkali and the glycerin are separated by " salting out, " and the soap in this condition contains about 30% of water.
The contents of the pan are once more allowed to cool and settle, and the soap as now formed constitutes a pure curd coap, carrying with it some proportion of uncombined alkali, but containing the minimum amount of water.