Experiment Station Record, Volume 45, July-December, 1921 Page: 12
xxvii, 995 p. ; 24 cm.View a full description of this book.
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12 EXPERIMENT STATION ECORD. [Vol. 48
the pressure. Sufficient alkali is then added to neutralize the HzS04, followed
by 2 cc. of the standard hypobromite solution. The pressure is reduced and the
apparatus shaken for about a minute to completely liberate the nitrogen. To
prevent liberation of oxygen from a possible excess of hypobromite, a small
amount of sodium pyrogallate solution is run into the reaction chamber as soon
as the decomposition of the ammonium salt is over. The volume of nitrogen is
best read by making the volume of the gas exactly 1 cc. and measuring the
pressure necessary to accomplish this. Corrections should be made for the
nitrogen content of the hypobromite solution and, if great accuracy is required,
for the quantity of nitrogen dissolved in the final solution.
Comparative results obtained by the above method and the Kjeldahl procedure
in nitrogen determinations with sodium sulfanilate, casein, uric acid, dried milk,
and urea are reported. While not having the accuracy of the Kjeldahl method,
the new procedure is considered to give results of ample accuracy for many
purposes and to have the advantage of being much more rapid.
Directions are also given for the application of the method to the determination
of the nonprotein nitrogen of blood, using the tungstic acid precipitation
method of Folin and Wu for obtaining a protein-free blood filtrate.
Determination of glucose and starch by the alkaline potassium permanganate
method, F. A. QUISUMBING (Philippine Jour. Sci., 16 (1920), No. 6, pp.
581-599, figs. 6).-The author reports a study of the conditions essential to the
accurate estimation of glucose and starch by the alkaline potassium permanganate
method, and describes a technique by means of which results have been
obtained which are said to be of an accuracy equal to that of volumetric
Fehling determinations. The standardized procedure for the determination of
glucose is as follows:
Fifty cc. of N/10 potassium permanganate solution, 25 cc. of a solution of
sodium carbonate containing 8.48 gin. of anhydrous sodium carbonate per liter,
and 25 cc. of the glucose solution (which should not contain more than 40 gm.
of glucose) are placed in an Erlenmeyer flask, which is then placed on a special
heating device so regulated that the temperature is raised from 29 to 95 C.:
in 2 minutes. The flask is heated for exactly 2 minutes after the temperature
has reached 95, after which it is removed, 25 cc. of 28 per cent H2SO and.
25 cc. of N/10 oxalic acid solution are added, and the excess oxalic acid is
titrated against N/10 potassium permanganate until the liquid assumes a pink
color which remains for a few seconds. The calculations are made from a table
of standards of glucose and starch.
In applying the method to starch analysis the washed sample is first hydrolyzed
with sulphuric acid. When flour is to be analyzed it should be hydrolyzed
by the saliva or diastase method, as the results by the permanganate
method are about 10 per cent higher after acid hydrolysis of the flour.
A volumetric method for the determination of lactose by alkaline potassium
permanganate, F. T. ADRIANO (Philippine Jour. Sci., 17 (1920), No. 2, pp.
213-220).-The method noted above has been applied to the determination of
lactose in milk with the use of lactose permanganate tables similar to those for
glucose and starch. Comparative results are reported of lactose determinations
with the permanganate method and the optical and Soxhlet methods on samples
of diluted evaporated milk, fresh and sterilized cow's milk, and a synthetic
milk prepared in the laboratory by mixing the necessary proportions of water,
butter, casein, pure lactose, ash, and water.
The percentages of lactose given by the optical method were consistently
lower than by either of the other methods, and the Quisumbing method gave
slightly lower results than the Soxhlet. The differences between the polari
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General Index to Experiment Station Record, Volumes 41 to 50, 1919-1924 (Book)
A topical, alphabetically arranged index to volumes 41-50 including experiment station records, publications reviewed, and foreign publications. In has a list of all editorial notes from the referenced volumes.
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United States. Office of Experiment Stations. Experiment Station Record, Volume 45, July-December, 1921, book, 1921; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc5009/m1/39/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.