Volume 2

Allen's commercial organic analysis : a treatise on the properties, modes of analysis, and proximate analytical examination of the various organica chemicals and products employed in the arts, manufactues, medicine, etc. with concise methods for the detection and estimation of their impurities, adulterations, and products of decomposition.

  • Allen, Alfred Henry, 1847-1904.
Date:
1911-1917
Catalogue details

Licence: Public Domain Mark

Credit: Allen's commercial organic analysis : a treatise on the properties, modes of analysis, and proximate analytical examination of the various organica chemicals and products employed in the arts, manufactues, medicine, etc. with concise methods for the detection and estimation of their impurities, adulterations, and products of decomposition. Source: Wellcome Collection.

    484/540 (page 468)
    when the copper, iron, zinc, magnesium, and more or less calcium will be dissolved as sulphates, and can be detected in the solution by the usual methods. The residue will contain lead sulphate, together, possibly, with calcium sulphate. On treating it with a hot solution of ammonium acetate, the lead sulphate will be dissolved, and the resul¬ tant solution will give a yellow precipitate with potassium chromate and a black precipitate with hydrogen sulphide. Calcium is a frequent impurity occurring most commonly as calcium oleate. It is most readily estimated by precipitating the diluted sample with ammonium oxalate. Precipitation in an alcoholic solution with sulphuric acid has been recommended by Cap, but pre¬ sents no advantages over the oxalate method. Alkalinity in commercial glycerol is due almost entirely to sodium carbonate, and is readily estimated by titrating the diluted sample with standard acid. Sulman and Berry recommend the use of litmus as an indicator, neither phenolphthalein nor methyl-orange giving sharp end-points. Glycerin from soap-lyes is purposely alkaline, owing to the risk of concentrating it in presence of acid. The alkalinity usually varies from 0.5 to 2.0%, depending to some extent on the manner in which the lyes have been treated. In a case cited by Fleming, in which the glycerin had been separated from the lye by alkali instead of salt, the resulting glycerin contained 31% of sodium carbonate. Chlorides cannot be estimated by direct titration or precipita¬ tion with silver, owing to the solubility of silver chloride in glycerol and the reduction of the nitrate by various impurities. The esti¬ mation is best made by allowing a weighed portion to burn away as already described, exhausting the carbonaceous residue with water, and titrating the filtered solution with N/10 silver nitrate, using neutral potassium chromate as an indicator. Crude soap-lye glycerins usually contain from 5 to 10% of salt. Sulphates may be estimated by precipitating the diluted sample with barium chloride. They are usually present in the product from soap-lyes, and sometimes in very large amount. Glycerins obtained by saponifying fat with sulphuric acid are always charged with sul¬ phates and often contain sulphites, thiosulphates and sulphides, the last three being objectionable. The milky precipitate produced on acidi¬ fying the raw product from soap-lyes sometimes contains a considerable proportion of free sulphur, the proportion amounting in some cases to