II. CHEMISTRY 197 



3 days. Inert gases or low temperatures greatly diminish, but do not pre- 

 vent, the decomposition. In the author's experience, a sample stored for 6 

 years in the dark at 0° in a closed but not hermetically sealed bottle, re- 

 tained its crystalline form but became deep yellow, and shortly after 

 warming to room temperature it mildly exploded. Huber and Barlow found 

 that samples sealed under vacuum in amber ampules and kept in the re- 

 frigerator, showed no change up to 9 months. The esters of calciferol 

 (Table VIII, page 204) with ^'arious nitrobenzoic acids are remarkably 

 stable and provide a means of storage as well as of characterization. They 

 remain unchanged over a period of years if a slight photodecomposition is 

 avoided by keeping them in amber bottles. -^'^ Fresh calciferol can then be 

 had at any time, merely by applying a simple saponification procedure 

 which avoids recrystallization and its attendant hazards to purity. Solu- 

 tions of calciferol in edible oils or in propylene glj^col, and dispersions of it 

 in canned milk, have excellent keeping ciualities, even under severe condi- 

 tions.297 



The melting point data on commercial calciferol are reviewed by Ander- 

 son et al.-^'^" The melting point is close to 116°, values between 115° and 

 117° being the usual range. Perhaps because of slight thermal decomposi- 

 tion, the actual melting point is unsharp. Highly purified calciferol melts 

 at 121°, according to Penau and Hagemann.-^" 



Calciferol is strongly dextrorotatory, although less so than lumisterol; 

 the presence of the latter as an impurity can be determined quantitatively 

 by a procedure described by Setz.-e The positive rotation decreases mark- 

 edly with increasing temperature; in alcohol this decrease amounts to 

 0.515° per degree of temperature rise.^^^" The dextrorotation of calciferyl 

 3,5-dinitrobenzoate, on the other hand, increases with increasing tempera- 

 ture. The specific rotations of both calciferol and its 3,5-dinitrobenzoate 

 increase substantially with the concentration of the test solution. The 

 effects of solvents on the specific rotation are even greater than for ergos- 

 terol, but in a generally reversed order, as shown in Table VII in com- 

 parison with Table VI. Since the specific rotation of calciferol is highest in 

 absolute alcohol, and also because calciferol is extremely sensitive to traces 

 of hydrogen chloride,"^ it is customary to determine the specific rotation 

 in alcohol, rather than in chloroform. 



The absorption spectra of calciferol and several of its substituted nitro- 

 benzoic acid esters have been studied by Huber et alP^ The curve for 

 calciferol is smoother than some pre\aously published and shows no evi- 

 dence of inflections other than the one broad band at 2G5 m/x. Identical 

 values were obtained in alcohol and hexane, and the curves were also 

 identical with those of vitamin Ds in the same solvents. The molecular 

 extinction coefficient of 18,200 is in good agreement with previously re- 

 297o F w Anderson, A. L. Bacharach, and E. L. Smith, Analyst 62, 430 (1937). 



