A system of materia medica and pharmacy : including translations of the Edinburgh, London, and Dublin pharmacopoeias / by John Murray.

  • Murray, J. (John), -1820.
Date:
1828
Catalogue details

Licence: Public Domain Mark

Credit: A system of materia medica and pharmacy : including translations of the Edinburgh, London, and Dublin pharmacopoeias / by John Murray. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

    22/576
    early period of the researches of pneumatic chemistry, the decomposition of Ammonia was effected, and it was found to be a compound of hydrogen and nitrogen. This suggested the conjecture, that the two fixed alkalis might be of similar composition, containing at least one or other of these elements as a common principle. This conclusion from analogy has not, however, been established. Sir H. Davy, by the application of galvanic action in high intensity, succeeded in decomposing potash and soda; the bases obtained from them are substances of a metallic appearance and lustre; and these bases are combined with oxygen. The analogy of the fixed alkalis to the common metallic oxides was thus so far established, and the earths being afterwards found to be of a similar constitution, this analogy was extended to them, and all those substances, distinguished by the common property of neutralizing acids, appeared to be of similar con- stitution. Ammonia alone remains insulated, and it presents the singularity, that while it possesses the same general properties, and strictly resembles the other alkalis in chemical qualities, no traces of oxygen can be discover- ed in its composition. The analogy, therefore, either fails with regard to it, or if it be an oxidated substance, nitrogen or hydrogen must be com- pound, and contain oxygen as an element. The bases of the fixed alkalis are substances of very peculiar proper- ties. They have the lustre, opacity, and tenacity of metals; but they want the most characteristic metallic property, that of density ; they are lighter even than water. They are very fusible, and pass through the changes of form, as well as different states of cohesion, within a very li- mited range of temperature. They are highly inflammable, they com- bine with oxygen with the phenomena of combustion, and are susceptible of different degrees of oxidation. These substances have been regarded as the simple bases of the alkalis ; but some facts favour the opinion that they contain hydrogen, and are metallic hydrurets, instead of being sim- ple metals. Potash, or as it ought to be named, (in conformity to the rule of giving a similar termination to the names of substances belonging to the same order), Potassa, is obtained from the incineration of vegetables, espe- cially the woody part; the saline matter remaining after the wood has been burnt, consists principally of this alkali, in combination with carbonic acid. It is freed from the impurities by lixiviation : the acid is abstracted by the action of lirne, the alkali is obtained in solution, and, by evapora- tion, can be obtained in a solid state. It is of a white colour, crystalliza- ble, fusible, and volatile at a red heat; abundantly soluble in water, so- luble also in alcohol, powerfully caustic, and possessed of all the alkaline properties in a high degree. There is some uncertainty whether it ex- ists in the vegetable matter from which it is procured in the state in which it is obtained, or whether its base is a constituent principle of that mat- ter, and is oxygenated during the combustion : one reason for admitting the latter opinion, at least in part, is, that the alkali cannot be extracted in so large a quantity by any other process as by burning. Potassium, as the base of potash has been named, is at the tempera- ture of 32° a solid substance, hard and brittle, of a white colour, opaque, and with the lustre of polished silver ; at 50° it becomes soft and malle- able ;at 70° the form of small globules ; somewhat mobile and liquid ; and at 100°, or according to Gay Lussac and Thenard at 136°, is completely so. It requires a temperature near to a red heat to volatilize it. It is light-