Salts and their reactions : a text-book of practical chemistry / by Leonard Dobbin and Hugh Marshall.

  • Doddin, Leonard, 1858-
Date:
1912
Catalogue details

Licence: In copyright

Credit: Salts and their reactions : a text-book of practical chemistry / by Leonard Dobbin and Hugh Marshall. Source: Wellcome Collection.

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    alhaJi, oblained by sublimation from dried animal matters (urine, etc.). Subsequently, it was discovered that new sub- stances, possessing the alkaline character in a much more marked degree, could be prepared from the first twd of these alkaline salts by the action of slaked lime on their aqueous solutions, and evaporation of the clarified liquids to dryness. On account of their highly corrosive action on organic tissues^ these new substances were called the caustic alkalies, and, in contradistinction to them, those from which they were prepared became known as the mild alkalies. These two classes of salts, acid and alkaline, were found to be mutually destructive of each other’s characteristic properties when their aqueous solutions were mixed, and, when the result- ing solutions were evaporated, substances were obtained ' which, like common salt, yielded solutions that were neither acid nor alkaline, and otherwise more or less closely resembled common salt in general behaviour. Such substances were, therefore, called mixed salts ” or compound salts.” To take a particular example : when spirit of salt was saturated ” with mild mineral alkali (soda), so that the solution no longer showed any acid character, and the resulting solution was evaporate, crystals of common salt were obtained. The same result wa§ arrived at by using caustic mineral alkali, the only different being that whereas in the former case the process of ^turation was attended with brisk effervescence, in the latter this was absent. “Alkaline salts” were not the only substances which could saturate “acid salts” to produce new salts of the mixed type; this property was shared by many of the “ earths,” which were substances conspicuously fire-resisting and insoluble in water. These earths included chalk and quicklime (which were looked upon as merely varieties of the same substance, although the latter was known to be somewhat soluble in water while the former was not appreciably soluble), magnesia, and the “calces” or ashes obtained when metals were heated in air. It was also known that certain metals, when dissolved by “acid salts,” saturated these and gave the same “mixed salts ” as were obtained from their calces. Notwithstanding the knowledge of salts and their properties which w^as thus gradually accumulated, no reasonable theory as to their real. nature was possible until the foundation of modern chemistry was securely laid, in the latter half of the eighteenth century, by the recognition of the true character of the chemical actions which take place during combustion and similar processes. The metallic calces were then found to be comjiounds formed by the union of the metals—elements —with oxygen—also an element; it was also found that many substances which formed acids in an aqueous solution
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