Elements of pharmacy.

  • Wills, George Sampson Valentine.
Date:
[1891]
Catalogue details

Licence: Public Domain Mark

Credit: Elements of pharmacy. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    Distillation is the changing of a liquid into vapour by means of heat, the vapour being condensed into a liquid by a cooling apparatus, known as a condenser, or by pressure. This process is applied in order to separate volatile from fixed substances. The fluid which passes over is called the distillate, that which remains in the retort, the residue. Fractional distillation is distilling a mixture of bodies at different temperatures in order to separate those substances which have different boiling points. Destructive distillation consists in decomposing bodies by heat in partly closed vessels ; the resulting vapours, being condensed, form new products. Decantation consists in gently pouring a liquid from one vessel into another. Ebullition is the process of boiling. When the evaporation is accompanied by bubbles of vapour, the fluid is said to be in a state of ebullition. The amount of elastic force exerted is termed its tension. A liquid boils when the tension of its vapour is sufficient to overcome the pressure of the atmosphere. Elutriation is the process of separating, by means of water, coarsely powdered substances when mixed with finely powdered bodies. The former sink to the bottom, whilst the latter remain suspended and are poured off. The solution on standing deposits the elutriated powder. Calamine and prepared chalk are treated in this way. Evaporation, or vaporisation, consists in the conversion of a fluid into gas or vapour at a temperature lower than its boiling point. When the whole of the liquid has been evaporated, it is said to be evaporated to dryness, the substance which remains is called the residue. This pro- cess is employed in the making of extracts, and in the crystallisation of certain salts. b 2 •3 ^