CURRENT LEPFERATURE 
NOTES FOR STUDENTS 
Estimation of plant carbohydrates.—In a series of papers from the Rotham- 
stead Experimental Station, Davis, DaisH, and SAWYER have reported the 
results of a critical study of existing methods for the estimation of carbo- 
series, on the estimation of maltose in solution with other sugars, Davis and 
DatsH' point out several sources of possible error in the gravimetric method 
of Brown, Morris, and Mittar. All samples of asbestos examined, even 
after previous washing in acid and ignition, contained an easily decomposed 
silicate, which was rapidly dissolved by the hot alkaline Fehling’s solution, 
thus giving weights which were uniformly too low. Digesting the asbestos for 
30 minutes with boiling 20 per cent NaOH and subsequent washing with water 
removes all material soluble in Fehling’s solution, and the authors recommend 
such digestion as a routine procedure. Since the precipitate of cuprous oxide 
obtained from plant extracts or from solutions previously subjected to fermen- 
tation by yeasts invariably contains copper salts of amino acids and adsorbed 
colloidal organic matter, the employment of the official method of weighing 
use of a blowpipe, in a powerful flame, subsequently weighing as cupric oxide. 
Of the more generally employed volumetric methods subjected to test, the 
Ling-Rendle method, employing an acid solution of ferrous ammonium sulphate 
and ammonium thiocyanate as indicator for Fehling’s solution, is accurate to 
at least 0.3 per cent, and is also much more rapid than the Bertrand per- 
manganate method. The latter was found to have an error of 1 per cent with 
maltose, 1.5 per cent with dextrose, while the results for cane sugar were 3.5 
per cent low, as the 2 per cent HCl used for inversion caused considerable 
decomposition of levulose. In eatenating cane sugar in solutions containing 
maltose, it is impossible to use HCl at 70° for inversion, since maltose is also 
hydrolyzed, while pentoses undergo decomposition; nor can 2 per cent citric 
acid be employed, since the use of basic lead acetate to precipitate tannins, 
amino acids, etc., and the subsequent precipitation of lead with Na,CQ,, 
* Davis, Wititam A., and Datsun, ARTHUR JouN, A study of the methods of esti- 
mation of chibelindeaton especially in plant extracts. I. A new meth or the 
estimation of maltose in presence of other sugars. Jour. Agric. Sci. 5:437-468. 1013- 
178 
