ANALYTICAL EDITION
2
273
+ t -- Va reduced to N. T. P. (t of Va when 9 was noted)
V , X 273 ~
=
temperature
As 5.1 cc. of carbon dioxide weigh 0.01 gram a t normal temperature and pressure, we obtain 0'01 loo = % carbon in sample 5.1 X 11 X wt. of sample
Cross and Bevan ( I ) , after many experiments, applied the following correction factor which considers the amount of carbon dioxide dissolved in the acid:
% carbon obtained X 0.4 25 and this result is added to the per cent carbon obtained above to give the true result. (a) Using c. P. succinic acid: 0.1025-gram sample; 5 mm. on inserting stopper; 126 mm. final pressure increase; t = 25" C.; Vi = 530.6 CC. X 300 X 0.01 [(630*6 881 - 530'6] 298 273 X 5.1 X 11 X 0.1025 40.4% carbon
m)
Vol. 4, No. 1 40 4
and - X 0.4 = 0.64 25 40.4 0.64 = 41.04% carbon (calcd. = 40.6%) (b) Using benzoic acid: 68.3 and 68.5% carbon found (calcd. =
+
68.8%)
(c) Using cellulose: 44.4 and 44.3% carbon found (calcd. = 44.4%)
As mentioned above, the method was originally planned for the analysis of cellulose compounds, and the writer mentions the fact that slightly erroneous results are obtained until one becomes familiar with the operation. Consistent results have been obtained having a maximum deviation of 0.5 per rent from the theoretical carbon content.
ACKNOWLEDGMENT The writer wishes to acknowledge his indebtedness to Ferdinand Schulze for assistance in constructing the apparatus.
LITERATURE CITED (1) Cross and Bevan, J . Chem. Soc., 53, 889 (1888).
RECEWBID February 5 , 1931.
Calorimetric Determination of Traces of Manganese and Chlorine with Benzidine R. C. STRATTON, J. B. FICKLEN, AND W. A. HOUGH,The Travelers Insurance Company and The Travelers Indemnity Company, Hartford, Conn.
I
T HAS been found that when benzidine hydrochloride is added to a very dilute solution containing the permanganate ion or free chlorine, or both, a brilliant blue-green color is produced. The following procedure has application wherever manganese is to be determined as permanganate ion in the absence of free chlorine. Conversely, this reagent may be applied as a test for free chlorine in the absence of the permanganate ion. AS compared to the determination of these constituents with ortho-tolidine, or by the direct estimation of the permanganate ion by its color, the following advantages and disadvantages have been noted. The blue-green color produced by benzidine hydrochloride is much more brilliant and consequently more favorable for colorimetric estimation than the natural color of the permanganate ion or its combination with ortho-tolidine in very dilute solutions. I n the case of the permanganate ion, the most favorable range in which to judge the color produced is that in which the amount varies from 0.0001 to 0.001 mg. in 100 cc. of the solution. The most favorable range in which to judge the color produced by free chlorine is that in which the amount varies from 0.001 to 0.01 mg. in 100 cc. of the solution. The great disadvantage of this method is the fading of the color produced. I n about 2 minutes the blue-green color changes to a yellow-green, which also is not persistent, a6d therefore the estimation has to be made immediately. This makes the preparation of an artificial color standard necessary. Such a standard can be prepared by mixing solutions of copper sulfate and picric acid. The presence of large amounts of sulfate should be avoided, since the sulfate ion reacts with benzidine base to produce a white crystalline precipitate which interferes with the accurate judging of the color.
The method employed in this laboratory is as follows: REAGENTS.Benzidine hydrochloride solution: 2.3 grams of benzidine base dissolved in 100 cc. of 5 per cent hydrochloric
acid.
PROCEDURE.A suitable aliquot of the material is taken so that the permanganate ion will be present in an amount between 0.0001 and 0,001 mg., or free chlorine present in an amount between 0.001 and0:Ol mg. The sample is diluted to 100 cc. and 1 drop of benzidme reagent is then added. The sample is immediately transferred to the colorimeter tube and matched against the standard. The artificial standard is prepared by making a 15 per cent solution of copper sulfate and adding to it the proper amount of 0.5 per cent solution of picric acid to produce the correct tint. After obtaining the identical blue-green tint which is produced by the addition of the benzine, the standard is diluted to such a concentration that 100 cc. will match in depth the amount of color produced by 0.001 mg. of permanganate in a solution of known permanganate content. Each cubic centimeter of standard used in matching the color produced will then equal 0.0001 mg. of permanganate ion. A parently this standard will keep indefinitely without change o f color.
A color standard for the determination of chlorine may be prepared in a similar manner. RECEIYEDJuly 13, 1931.
SUNSHINE VITAMINMADE IN LABORATORY. A vitamin has been manufactured in the laboratory by strictly chemical methods for the first time in history, Charles E. Bills and Francis G. McDonald of the Mead, Johnson and Co. Research Laboratories, Evansville, Ind., reported at the meeting of the American Association for the Advancement of Science in New Orleans. They synthesized vitamin D by treating ergosterol with nitrogen monoxide gas and obtained the potent vitamin without ultraviolet radiation. The synthesis of the vitamin is carried out in solution with methyl alcohol, ether, and ethyl acetate a t low temperature and with rigid exclusion of oxygen.
