mainly by Scandinavian chemists, is the use of titratable derivatives for identification of class types and equivalent weight such as the xanthates of primary and secondary alcohols. Steric and electrostatic effects are illustrated by the dicarboxypyridines and 2amino-4-azapentanes and homologs. The effect of the solvent is illustrated by the great difference of the basicity of substituted oxazolines, imidazolines, and hexahydropyrimidines in water and acetic acid, and by the acidity of alkylnitronic acids in water and in mixed solvents. The work of Brackmann and hleyer on acid functional groups in a microbiologically produced antibiotic-type material introduces the use of nonaqueous titrimetric methods as an aid in the proof of structure.
Quantitative Organic Microanalysis.
WOLFGANG SCHONIGER, Sandoz, Ltd.,
Basle, Switzerland.
Since quantitative organic microanalysis was introduced by F. Pregl some 40 years ago, significant progress has been made. The various procedures for organic microanalysis are discussed, particular consideration being given to methods that have been investigated in the Microanalytical Laboratory of Sandoz, Ltd., or in the Pregl Laboratory a t the University of Graz. Carbon and Hydrogen Determination. New developments are discussed from three points of view: modifications in conditions of combustion, modifications in apparatus for the absorption of nitrous oxides, and introduction of new methods for determining the final products, carbon dioxide and water. Particular attention is paid to all those methods which have proved suitable for routine use. A method for the simultaneous determination of carbon, hydrogen, and nitrogen, which is being given a trial, is discussed in detail. Nitrogen Determination. Xumerous improvements proposed for dry and wet
methods of determination are discussed in the light of personal experience. Oxygen Determination. This method, which wasdevelo ed some 20 years ago, has become one of t i e most important procedures, for it has made possible direct determination of all elements in organic compounds. The difficulties arising from the special conditions under which the. work has to be carried out are discussed in detail. Halogen and Sulfur Determination. Methods for determining these elements have developed in two ways: improvement in the decom osition process (converting the organic suistance into simple inorganic halogen or sulfur compounds), and new methods for the final determination of halogen or sulfur. A new decomposition process developed in the Microanalytical Laboratory of Sandoz, Ltd., is demonstrated and discussed in detail. Finally, mention is made of methods used for determining other elements and a report is made on experience gained in daily practice.
150. Diuranyl Chromate Uranium Trioxide Tetrahydrate, 2U02Cr0,.U03.4H20 R. M. DOUGLASS and EUGENE STARITZKY The University of California, 10s Alamos Scientific Laboratory, Los Alamos, N. M.
of t h e previously E undescribed compound diuranyl chromate uranium trioxide tetrahydrate, UHEDRAL CRYSTALS
2UOzCr04.UOa.4Hz0, were prepared b y B. J. Thamer of this laboratory by heating a n aqueous solution 0.6M in uranium trioxide and 1.OM i n chromic acid at 300" C. under a n initial oxygen pressure of approximately 100 pounds per square inch. T h e principal solid phase formed is insoluble in cold or hot water and not quickly soluble in acids. Spectrographic analysis showed uranium and chromium with only traces (less than 0.01%) of other detectable elements. Quantitative chemical analysis of a purified sample gave t h e following weight percentages: 63.3 uranium, 6.0 water (by the Penfield method), 9.5 (0.4-gram sample) and 9.1 (2.2gram sample) chromium. Taking 9.2% as t h e weighted mean chromium content leads t o the atomic ratio U/Cr = 1.50 or 3/2 and suggests the formula 2UOzCr04.UO1. 4H20 (calculated weight percentages 63.19 uranium, 9.20 chromium, 6.38 water). A plot of total weight loss as a function of tem-
314
ANALYTICAL CHEMISTRY
perature on heating a n impure sample (principal contaminant chromium sesquioxide) showed rapid loss at around 300" C., a marked plateau between 455" and 560" C. at 6.0%, further
C
rapid loss between 600" and 700" C., and a further plateau between 800" and 1000" C. a t 10.8%. The first plateau at 6.0% tends to confirm four water molecules per formula unit.
C
Figure 1, Orthographic projections of crystal of diuranyl chromate uranium trioxide tetrahydrate ( 1 00)and parallel to b axis
Close agreement between measured density and density calculated from cell dimensions assuming t h e above formula (see below) substantiates this composition. Gmelin ( I ) lists two basic uranyl chromates, 2U02Cr04.UO,. 81320 and U02Cr04.UOS. 6Hz0, neither of which appears t o correspond t o t h e present phase, although physical data are lacking.
Partial Powder X-Ray Diffraction Pattern of Diuranvl Chromate Uranium Trioxide Tetrahydrate
hkl 200 011 002 211 102 211 102 310 202 012 202 112 020 311 400 220 410 302 411 221 312 411 320 402 500 022 122 013 321
CRYSTAL MORPHOLOGY System and Class. \lonoclinic, prismatic. Habit, { 100) prominent, n-ith { 217 i and {201}. Cleavage. ( loo} prominent. X-RAYDIFFRACTION DATA Diffraction Symbol. 2 / ~ n P 2 ~ / indicatc, ing uniquely space group P21/c ( C i h ) . Cell Dimensions. a. = 16.637, bo = 8.385, co =010.490 A., all i
