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.

    48/768 (page 36)
    an equal weight of recently slaked lime, and as much wUj ter as is necessary to give the consistence of a thin paste: this is put into a glass funnel, the tube of which is ob- structed with a piece of linen ; the mass of lime soon sub- sides, so that the liquid portion filtrates through it slowly, and water is occasionally added, as the filtration proceeds, until a quantity of liquid has passed through, ten times the weight of the carbonate of potash employed. The lime in this process attracts the carbonic acid from the potash, and, from the large quantity employed, and the slowness with which the dissolved alkali passes through it, the ab- straction is more complete than could be obtained by any other arrangement. Still, the potash is not perfectly pure ; a little carbonic acid remains combined with it, and there may also be pre- sent small portions of sulphate and muriate of potash and silex. To obtain it in a state of purity, the method gene- rally followed is one proposed by Berthollet. Potash is soluble in alcohol, but is insoluble when combined with carbonic or sulphuric acid. The potash to be purified is therefore digested in alcohol, the impurities remain dis- solved in water in a lower stratum, while the alcohol holding the pure alkali dissolved, floats above; this is drawn off, and is partially evaporated in a silver bason. The upper portion of the liquor is again poured off, and is evaporated, so that on cooling it shall either deposite crystals, or pass into an irregular crystallized mass; this is the pure potash. Still, even after these processes, so strong is its attraction to carbonic acid, and such the in- fluence of quantity of matter, that it retains a minute por- tion of that acid, appearing even to abstract carbon from the alcohol. D’Arcet has recommended to add to its so- lution barytic water, which may render it perfectly pure. Potash thus prepared is when dried a solid mass, hard.