Nov., 1934
COMMUNICATIONS TO THE EDITOR
tential) and the corresponding pH value. The equation for this relationship is Loglo E = -0.0633 PH
+ 0.4080
2501
Assuming the formula to be K8PaF.r and protactinium to have an atomic weight of 231,61.29 and 39.40 parts, respectively, should have been obtained. This agreement definitely establishes the pentavalency of protactinium and the formula PazOs for the oxide. The two final determinations gave the following results :
where E is the absolute potential of the benzaldehyde electrode. In contrast to the quinhydrone system, the benzaldehyde system is irreversible. The chemical change involved seems to be the reduction of KaPaF7, g. PaaOs, g. 2KrPaFi:ParOj At. wt., Pa benzaldehyde to benzyl alcohol; hydrions and 0.091907 0.056274 1 .6332 230.4 electrons both being present, a potential with ,070047 .042913 1 ,6323 230.8 reference to the other half-cell (calomel) is inFor the atomic weights of the other elements fluenced by the pH of the solution into which the the 1934 values of the International Committee benzaldehyde is stirred. DEPARTMENT OF CHEMISTRY THOS. C.HERNDON were used [G. P. Baxter, Mme. P. Curie, 0. EASTERN TEACHERS COLLEGE Honigschmid, P. Lebeau and R. J. Meyer, THIS RICHMOND, KY. 56, 753 (1934)l. DEPARTMENT OF CHEMISTRY HANORA. WEBB JOURNAL, FOR TEACHERS GEORGE PEABODY COLLEGE The mean value of the atomic weight of protacNASHVILLE, TENN. tinium is 230.6, or in whole numbers 231, with RECEIVED AUGUST 2, 1934 an accuracy of about *0.5 unit. This value is in complete agreement with F. W. Aston’s results on actinium lead (AcD = 207)) obtained by THE ATOMIC WEIGHT OF PROTACTINIUM means of his mass spectrograph. Sir: For a precision atomic weight determination Part of the one tenth gram of protactinium the analysis of the recently discovered PaCls oxide, recently isolated by M. S. Agruss and the [A. V. Grosse, THISJOURNAL, 56, 2200 (1934)] writer [THISJOURNAL, 56,2200 (1934)l has been will probably be more suitable; however, the used for the first direct determination of the latter can be used to its full advantage only atomic weight of protactinium. An x-ray photo- when larger quantities of protactinium will be graph of this material kindly taken by Dr. W. C. available. Such a determination is planned in Pierce had shown no impurities. the future. The classical method of M. C. de Marignac We are much indebted to the management of [Ann. chim. phys. [IVj 9,250 (1866)]for tantalum the Universal Oil Products Co., Chicago, for placwas utilized for this determination. Potassium ing a t our disposal the facilities of their Research protactinium fluoride (K2PaF7) was prepared Laboratories. from the oxide. It crystallizes in beautiful color- KENTCHEMICAL LABORATORY A. V. GROSSE less sharp long needles, very insoluble in water UNIVERSITY OF CHICAGO ILL. containing 0.5% of hydrogen fluoride. It is CHICAGO, RECEIVED OCTOBER 3, 1934 stable in air and can easily be dried to constant weight at 20 or 100’. This was reconverted into the oxide by fuming with sulfuric acid, diluting HALOGENATION INHIBITION BY OXYGEN with water, precipitating with ammonia, filtering the hydroxide, and igniting and weighing as oxide. Sir: Bauer and Daniels [THISJOURNAL, 56, 2014 All operations were carried out in and with (1934) ] present evidence for the inhibition of platinum equipment. All the chemicals were of cinnamic acid by oxygen the halogenation highly purified. A very sensitive ultra microbalance [K. W. H. Kiihlmann, Hamburg, Ger- and in their last paragraph suggest that the many] was used; all weights were corrected to influence of oxygen on reactions of this type may vacuum. Further details will be given in a be quite general. In these Laboratories the inhibiting effect of subsequent paper. The first preliminary analysis gave 61.18 parts oxygen on certain halogenation reactions has of the oxide and 39.67 p.arts of potassium sulfate been observed in many instances, and is the per 100-parts of potassium protactinium fluoride. subject of patents granted to this Company.
