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.

    120/768 (page 108)
    of silj^ium is inferred by Dr Thomson, to be 8, or equal to that of oxygen; the equivalent of silica is therefore 16. The process by which Silex, or Silica as it is sometimes named, is usually obtained, consists in fusing calcined flint with four times its weight of carbonate of potash. The mass, when cold, is dissolved in water, and diluted sul- phuric acid is added to the clear solution as long as any precipitation ensues; the precipitate is washed with wa- ter, and dried. It appears, however, not to be pure silex, but to retain a portion of alkali in combination. Colour- less rock-crystal, pounded, probably affords it more pure. Silex procured by precipitation is in the form of a light white powder, insipid and gritty to the touch ; when mix- ed with water, it does not form an adhesive paste. It is so infusible, as to melt only in the intense heat excited by an inflamed mixture of hydrogen and oxygen gases. It is not dissolved in any appreciable quantity by wa- ter, yet there are facts which prove its solubility to a cer- tain extent when this is not counteracted by its aggrega- tion : if the solution of its compound with potash be de- composed by an acid, no precipitate appears, if the solu- tion has been previously very largely diluted with water, though otherwise it would be apparent; and it exists in solution in some mineral springs, as in the Geyser foun- tains of Iceland, in which no substance that can contri- bute to its solution can be detected. When newly form- ed by the oxygenation of its base, Berzelius found it to be extremely soluble. This earth combines with the fixed alkalis, either by being boiled with them in water, or by fusion from heat. When one part of flint or quartz is melted with three parts of carbonate of potash, the carbonic acid is expelled, and the compound of silex and potash is partially soluble