William A. Davis

A Study of the Methods of Estimation of Carbohydrates, especially in Plant-extracts: A New Method for the Estimation of Maltose in presence of other Sugars.

Certain sources of error encountered in the estimation of sugars in plant extracts are dealt with. Large errors in the gravimetric method may be obtained unless special care is taken in purifying the asbestos by boiling for at least 30 minutes with 20% sodium hydroxide. Weighing the reduced copper as cuprous oxide is likely to give rise to large error, and a process of weighing as cupric oxide, with certain precautions, is recommended. The volumetric methods of Ling and of Bertrand have been studied; the former is preferable in all respects to the latter, which we regard as only roughly approximate. In dealing with plant extracts, owing to the accumulation of sodium acetate in the solutions analysed, inversion by citric acid of lower concentration than 10% is generally incomplete. Inversion by invertase is, however, not interfered with by this salt. To estimate cane sugar inversion both by invertase and 10% citric acid is recommended. No loss of sugars occurs owing to the use of basic lead acetate as has been sometimes stated; the supposed loss is probably due to incomplete inversion caused by the presence of sodium acetate. It is shown by a detailed study of the action of dilute hydrochloric acid on different sugars that it is impossible completely to hydrolyse maltose at either 70° or 100° without simultaneously destroying large quantities of laevulose or dextrose. The only available method for the accurate estimation of maltose consists in the employment of special maltase-free yeasts, such as S. exiguus, S. marxiarnus or S. anomalus , introducing a correction (for pentoses, etc.) obtained by a special fermentation with bakers or brewers yeast. 6. A scheme for the quantitative estimation of sugars in plant material is given.

A Simple Laboratory Apparatus for the Continuous Evaporation of Large Volumes of Liquid in vacuo

It is frequently necessary, especially in dealing with plant and animal extracts, to concentrate large volumes of liquid in vacuo . In such cases, the operation is often a very tedious one, owing to the necessity of closely watching the apparatus so as to control frothing and avoid the passing over of the liquid into the distillate. Having experienced this, more particularly in the distillation of alcoholic plant extracts, which show a great tendency to froth, the simple apparatus shown in the sketch has been devised which completely overcomes all the difficulties encountered in such work.

The Estimation of Potassium, especially in Fertilisers, Soil Extracts and Plant Ashes

It is shown that whereas the platinum chloride method of estimation is uncertain and liable to give varying results, the perchlorate method described is at once more simple in manipulation and more uniform and exact in its results. An improvement has been introduced which consists in washing the perchlorate precipitate with 95% alcohol saturated with potassium perchlorate by means of which any error due to the solubility of the precipitate is obviated. This is of importance when dealing with small quantities of precipitate. The following other advantages may here be enumerated:

Note on the loss of phosphoric acid during fusion with ammonium fluoride

1. When salts or minerals containing phosphoric acid are ignited with ammonium fluoride as in the ordinary process of analysis of silicates, considerable loss of the phosphoric acid may occur. It is probable that the phosphorus is volatilised in the form of a phosphorus fluoride. 2. The loss is least in the case of salts containing an alkali metal. It is less in the case of disodium hydrogen phosphate than in that of potassium dihydrogen phosphate, and is greatest in the case of phosphates of the alkali earth metals, such as calcium phosphate or apatite.