On the acetates and other compounds of alumina / by Walter Crum.

Date:
[1853?]
Catalogue details

Licence: Public Domain Mark

Credit: On the acetates and other compounds of alumina / by Walter Crum. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    ammonia, and lime have an equally powerful effect. The coagulum they produce is partially re-dissolved when the alkali is saturated by acetic or by muriatic acid. The salts which are thus formed render the solution somewhat oily. A boiling solution of potash or soda dissolves the coagalum, and at the same time changes it into the ordinary alumina, which is thrown down in the state of terhydrate when the alkali is saturated by an acid. Oil of vitriol also dissolves the solid part of the coagulum, and the same substance dried; especially when assisted by heat. Strong muri- atic acid, at a boiling heat, does the same, though with greater difficulty; and the products are the ordinary sulphate and muriate of alumina. Large quantities of the acetic salts may be added before they coagu- late the aluminous solution.* When the solid part of the coagulum produced by a strong solution of acetate of soda was afterwards freed from that salt by pressure, it re-dissolved in pure water, and the solu- tion was again coagulated by a fresh addition of the salt. An experi- ment with acetate of lime gave the same result. The nitrates and chlorides coagulate also with great difficulty. Solutions of sulphate of soda, magnesia, and lime coagulate as readily as a liquid containing the same quantity of sulphuric acid in the free state. On examining one of these mixtures, the sulphuric acid was found in the solid part of the coagulum, as before; and the mixture remained neutral. A small spoonful taken into the mouth becomes immediately solid from the effect of the saliva. The digested solution of alumina which has not been deprived of its acetic acid by boiling, requires about twice as much sulphuric acid to coagulate it as does the boiled solution. One of the most characteristic properties of the digested and altered acetate of alumina is its loss of the power of acting as a mordant. The ordinary acetate, as is well known, forms a yellow opaque precipitate with decoction of quercitron. That which has been thoroughly digested is merely coagulated by that decoction,—the colour of which is but little altered, and the coagulum is translucent. The same effect is produced with decoctions of logwood, brazil-wood, &c. A quantity of the solution of hydrate of alumina was evaporated to dryness at the heat of boiling water. After being pulverised and again submitted to the same heat, it was moistened with sulphuric acid as before described, and heated to whiteness. It lost 25'67 per cent, of its weight. Hydrate from the Insoluble Binacetate.—It has been already mentioned that when the precipitated binacetate is kept for an hour or two in 200 parts of boiling water, it is changed into the soluble binacetate. It must be constantly agitated during that time. The substance so pro- duced may be converted, like the original solution into the peculiar bihydrate. Thirty to thirty-six hours digestion is sufficient to complete the change, for after that time the solution has no longer any taste of alum, and the power of coagulating with acids does not increase. * Hence, in preparing tlie binacetate of alumina wliich is to be used in obtaining tlie bihydrate, it is better to employ an excess of acetate of baryta, than to leave in the solution the slightest trace of sulphuric acid.
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