NOTES
1594
Vol. 62
numbers in fused salts, including the “bubble cell,”’ may be arranged to have the following indicator radioactive tracer2 and modified Hittorf methods.a ion on the top or the bottom of the cell, depending The present paper describes a method based upon the density relationships. upon the visual observation of the boundary between the salt under investigation and a followHEATS OF COMBUSTION. VII. THE ing indicator salt. The chief advantage of the method lies in the removal of the requirement for HEATS OF COMBUSTION O F SOME AMINO a reversible metal electrode. ACIDS
Experimental The apparatus consisted of a U tube, one leg of which contained a Pyrex ca illary six cm. long with an internal radius of 0.5 mm. &he lower end of the capillary was joined to a larger tube (10 mm. i.d.) containing a Pyrex ultrafine disk with a pore size of 0.9 to 1.4 p . The volume between the disk and the capillary is kept to a minimum. The other leg of the capillary was an extension of the 10 mm. tubing. At the top, both arms of the U tube were enlarged to 20 mm. i.d. to contain the electrodes and to make changes in head during a run negligible. The apparatus was placed in a vertical tube furnace containing a window. Lead chloride, prepared by recrystallizing analytical grade salt, was used to fill the large-diameter leg of the cell and finally, when molten, was forced through the disk and to the top of the capillary by the application of a vacuum to the leg of the apparatus containing the capillary. Only a small volume of molten lead chloride passed through the disk, since the apparatus was designed with a small volume between the disk and the top of the capillary. The time required for filling the cell was about four hours. The zinc chloride, prepared by direct union of zinc metal with chlorine gas, was used to fill the upper portion of the U tube leg containing the capillary. The boundary between the molten salts was observed easily and remained sharp due to density difference. An alternating current was applied to the cell, and the boundary observed with a cathetometer. The heads of liquid in the two legs of the U tube were carefully balanced by the addition or removal of lead chloride from the cathode side after spectrographic carbon electrodes had been inserted into salt in the arms of the cell. When the boundary was observed not to move for a period of one-half hour, direct current was substituted quantitatively for the alternating current, and measurements on the motion of the boundary were made. The anode was placed into the zinc chloride and the cathode into the lead chloride. Thus the zinc ion was made to follow the lead ion. A number of observations were made during the course of a run. It is necessary to keep air containing moisture away from the zinc chloride, or i t becomes too viscous to pass through the capillary easily.
Results The transport number is calculated by means of an equation, assuming that the only flow through +,hedisk is due to electrical transport t+
prR2 X 96500 X Ah equiv. wt. of salt X amperes X seconds
where density of salt at temp. of run = diameter of capillary at temp. of run Ah = difference of height a t beginning and ending of run
&
=
The result of ten runs including 80 observations 0.04 at 550’ in excelon PbC12 was t f = 0.24 lent agreement with the value reported by other methods. The current used was 20 ma. The requirements for a following ion are that it be of sufficiently different density to make a good boundary and that its total conductivity be less than the salt under investigation. The membrane must be in the salt being investigated; the cell
BY TOSHIO TSUZUICI, D. 0. HARPERAND HERSCHEL HUNT Department of Chemistry and Purdue Research Foundation, Purdue University, Lafayette, Indiana Received June 6 ,1968
The heats of combustion of L-isoleucine, glycine, L-phenylalanine, L-tryptophan, L-threonine and Lalanine have been determined by means of a nonadiabatic calorimeter. The method is exactly the same as that described by previous workers in this Laboratory. The acids were furnished by Dr. J. P. Greenstein of the National Cancer Institute, Bethesda, Maryland, and are better than 99.9% pure. The heats of combustion of the amino acids at constant volume and 25” for the reaction producing gaseous carbon dioxide, gaseous SO3, liquid water and gaseous nitrogen, are given in Table I. The standard deviations were calculated in accordance to the recommendations of Rossini and Deming.2 The atomic weights for the computations are 0 = 16, C = 12.011, H = 1.0080, S = 32.07, and N = 14.008; 1 thermochemical calorie = 4.1833 int. joules. TABLE I Amino acid
L-Phenylalanine (s), CsHllOzN L-Tryptophan (s), CI~HIZOZNZ L-Isoleucine (s), C~H1302N L-Threonine (s), CdHs03N L-Alanine (s), CaH702N Glycine (s), CzHaOzN L-Methionine (8) , C~HIIO~SN
Heat of Combustion, koal./rnole
1110.5 i 0 . 2 1345.5 i . 2 855.2 & . 2 490.9 i . 2 376.9 f . 5 230.9 i . 2 759.2 f . 2
The heat of combustion of L-phenylalanine is given in the literature3as 1,114.05 kpal./mole. The heat of combustion of insulin was found to be 5,382.2 f 0.2 cal./g. The authors wish to express appreciation t o the National Science Foundation for sponsoring this research and to Dr. John 0. Hutchens of the University of Chicago for coordinating it with his entropy work. (1) T. Tsuzuki and H. Hunt, THISJOURNAL,61, 1668 (1957). (2) F. D. Rossini and W. E. Deming, J . Wash. h a d . S c i . , 29, 416 (1939). (3) E. Fischer and F. Wrede, Akad. wiss. Berl Sitzungsber., 687 (1904).
+
(1) F. R. Duke and R. W. Laity, THISJOURNAL, SO, 549 (1955). (2) F. R. Duke and R. A. Fleming, J . Electrochen. S O C .in , press. (3) F. R. Duke and J. P. Cook, Iowa Slate Coll. J . Sei., 32, 35 (1957).
THE VAPOR PRESSURE OF CADMIUM AND ZINC CHLORIDES BY H. BLOOMA N D B. J. WELCH University of Auckland, Auckland, New Zealand Received June 19, 1968
In the course of an investigation of the vapor pressures of molten salt mixtures, the vapor pressures of pure CdClz and ZnClz were determined by
