Foods, their composition and analysis : a manual for the use of analytical chemists and others : with an introductory essay on the history of adulteration / by Alexander Wynter Blyth.

Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: Foods, their composition and analysis : a manual for the use of analytical chemists and others : with an introductory essay on the history of adulteration / by Alexander Wynter Blyth. 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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    solubility. Leaving for the present the special tests, the minaber and natui-e of the constituents which requii-e to be determined for the purpose of the food-analyst, vary according to the par- ticular substance under examination, e. g.— In all substances, the percentage. In such fluids as milk, the alkaline jyhosphates and the chlorides. In seeds, such as wheat, cocoa, &c., the total phosphoric acid. In beer-ash, the amount of common salt. In bread-ash, the presence or absence of alumina, magnesia, and proportion of silica to alumina. In tea-ash, the alkalinity, the iron, the silica, and proportion of soluble to insoluble ash. In cofFee-ash, likewise the proportion of soluble to insoluble ash, but the presence or absence of silica becomes also of im- i:)Oi-tance. From these illustrations (which might be multiplied) it follows that, for the purposes of the food-analyst, the general constitution of the ash will be sufficiently known when the following deter- minations have been made :— . (1.) The total percentage of ash. (2.) The total percentage of ash soluble in water. (3.) The total percentage of ash soluble in acid. (4.) The alkalinity of the ash. (5.) The percentage of chlorine. (6.) The percentage of phosphoric acid. (1.) The Total Percentage of Ash.—Of the various methods of estimating an ash, the simplest and most practical appears to be —to place a sufficient quantity of the substance to be burnt in a capacious platinum dish, and to consume at the lowest possible temperatiire by heating with a ring burnei'.* The qiiantity to be taken is regulated by the amount of ash in the substances. For example, flour, containing only 7 per cent, of ash, would give with 50 grms. '35 ash, which is about as small a quantity as it is possible to work with conveniently, whilst in the case of cofl'ee, tea, and cocoa, from 5 to 20 grms. is for most purposes ample. * If the sulphuric acid in the ash is not to be determined, a wide glass tulie (such as the chimney of a common paraffin lamp) adjusted over the dish, by its powerful up-draught greatly expedites the operation ; but if the sul]>huric acid is to be determined, the impure gas of commerce renders the results too high. It is, however, of course open to the aualyst to make the gas pass through a proper absorption-apparatus, or to use as a fuel, alcohol.
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