Page:Scientific Memoirs, Vol. 1 (1837).djvu/172

 The undissolved portion of the oxide, which has also acquired a brownish black colour, possesses the same property.

The greater number of the compounds of the metals with spiroil may be obtained by double affinity, but for this purpose the spiroilic combinations must be difficultly soluble or insoluble, and very concentrated solutions of easily soluble salts must be employed. For this reason, in order to obtain the combination with lime, solution of chloride of calcium is employed; for the combination with zinc, acetate of zinc; for the magnesian compound, chloride of magnesium; and for the compounds with iron, the proto- and the sesqui-chloride of iron. The best combination of spiroil to employ is the hydrospiroilate of ammonia, over which the concentrated solution of the salt is to be poured. The spiroilide of barium, which is be&t obtained by saturating baryta water with the acid, may be advantageously employed in the state of a solution for the preparation of several of the compounds of spiroil. The compounds as obtained by double decomposition are seldom crystalline, but are obtained almost always as a fine and soft powder.

Spiroilic Acid.

If hydrospiroilic acid be gently and carefully heated with nitric acid not too concentrated, and care be taken that the acid be not used in excess, the oil is converted under evolution of nitrous fumes into a solid crystalline body; the substance thus obtained is spiroilic acid.

If the gas which is evolved during this operation be conducted into a solution of chloride of barium mixed with ammonia, not the slightest trace of carbonate of barytes will be formed.

The acid is nearly devoid of odour: its taste is at first not striking ; afterwards however much irritation in the throat, and a strong inclination to cough are experienced. Spiroilic acid is fusible, and shows strong inclination to crystallize, especially on returning to the solid state after having been heated. In close vessels it may be sublimed; nevertheless by this operation the greater part is decomposed, leaving behind a carbonaceous mass.

In the anhydrous state, as it is obtained by fusion, spiroilic acid is of a pale yellow colour.; if however it be exposed to the air it deliquesces and becomes of a deep yellow colour. It is easily soluble in alcohol and æther; only slightly so however in water. The solutions stain the skin and nails permanently yellow. Litmus-paper is stained deep yellow; no reddening effect can however be observed. If the alcoholic solution of the spiroilic acid be left to spontaneous evaporation, the acid is obtained in delicate transparent prisms of a golden yellow colour.