Elements of chemistry, in two volumes / by John Murray.

  • Murray, John.
Date:
1828
Catalogue details

Licence: Public Domain Mark

Credit: Elements of chemistry, in two volumes / by John Murray. Source: Wellcome Collection.

    49/768 (page 37)
    and brittle, of a greyish-white colour. It may be obtain- ed crystallized in thin plates, in slender needles, or in tetrahedral pyramids, single or double, these containing different portions of water of crystallization. They pro- duce cold in dissolving in water, while the solid potash produces heat. Even in the driest form to which it is re- duced by evaporation, and after it has been kept in fusion, the potash retains a considerable quantity of water com- bined with it, and which cannot be abstracted from it; as by applying heat to expel it, the potash itself is at length volatilized, along with its combined water, which is sepa- rated only when it enters into combinations. This im- portant fact was discovered by D’Arcet. The quantity of water seems to be one atom, 9, to one atom of potash, 48; hence the equivalent of the compound, Hydrate of Potash, as it is called, is 57. The combined water gives rise to a considerable modification of properties. The real alkali is supposed to be obtained by the combus- tion of potassium, and heating the product, so as to expel the excess of oxygen. It is of a greyish colour, harder and heavier than fused potash, with a vitreous fracture; it requires a strong red heat to melt it, and a higher heat to volatilize it. When a little water is add- ed to it, it becomes white and more fusible and volatile. It is uncertain what the properties of this compound are, whether it has any alkaline quality or not; for it cannot be submitted to examination without the admission of water, which immediately changes its composition, con- verting it into the hydrate. The hydrate melts at a heat of 360°, and is volatilized at a low red heat. It still has a strong attraction to an additional portion of water: it imbibes it rapidly from the atmosphere, so that its sur- face becomes humid, and it dissolves in less than its own weight of water, forming a solution dense and somewhat viscid.