NOTES
April, 1954 a small weight loss a t zero time. However, in view of the peculiar nature of the initial stages of the decomposition, it was not thought worthwhile to try to match the early stages of the curves.
c
tion. These data are not sufficient to make possible a classification of frequencies, but it does seem reasonable to assign 1345 em.-' to the nitroso N-0 stretching frequency.6 (5) E. Lieber, D. Levering a n d L. Patterson, Anal. Chem., 2 8 , 1504
TABLE I T ,'C. k , hr.-1
383
114
117
125
130
0.0094 -0,920
0.0172 -0.772
0.0360 -0.800
0.128 -0.923
Discussion The results of the weight loss measurements on the solid show no unusual characteristics. They show the qualitative features indicated by Tobin, Fowler, Hoffman and Sauer,2 and these are ascribed t o the same general phenomena. The gas evolution curves are quite interesting. The decomposition evidently remains in an induction period for an extended period, the induction period ending suddenly in a very sharp increase in reaction rate. This indicates violent autocatalysis of solid CTT by its gaseous reaction products, since no such phenomenon appears in the weight loss experiments, where the gaseous products are allowed to escape. It is not clear why the rate of gas evolution is the same for the 0.1150-g. sample as for the 0.5390-g. sample during the induction period or why the induction period for the smaller sample is only twice that for the larger sample. The larger sample showed no sign of fusion a t any time, but the smaller sample started to fuse during the sharp rise in pressure. The experiments were stopped when the pressure in the tube reached one atmosphere. When the sample tubes were opened to the atmosphere, brown fumes formed, showing that one of the gaseous products is nitric oxide. Sigmoid curves of the type obtained here for the melt may arise as the result of an equilibrium reaction, a sequence of consecutive reactions, or an autocatalytic reaction. The first possibility may be disregarded, due to the continuous removal of reaction product from the system. Other than this, little may be said about the mechanism. It is of interest to note that equation 1 has the same algebraic form as the equation representing the loss of reactant or evolution of non-catalytic product for seperal types of autocatalytic reactions. There is no doubt that the reaction is a complex one, so that the activation energy calculated from IC in equation 1 must be regarded as a composite quantity. The Infrared Spectrum of Cyclotrimethylenetrinitrosamine.-In the course of this work, occasion arose to obtain the infrared spectrum of cycIotrimethylenetrinitrosamine. The spectrum was obtained in Nujol mull on a Perkin-Elmer automatic recording spectrophotometer a t Arthur D. Little, Inc. The region 650-1400 cm.-l was covered with a NaCl prism, the region 1400-3500 em.-' with a CaFzprism. The observed bands, in cm.-l are 3050 (m), 2960 (s), 2890 (E)*, 1485 (9, v. br.) 1442 (br)*, 1370 ( I x ) * , 1345 (8, br), 1300 (s), 1255 (s) 1150 (m), 1075 (5, br), 995 (m), 952 (s, br), 875 (s), 800 (m, shoulder to 875), 840 (m);765 (s), 700 ( 9 )
The asterisks represent regions of Nujol absorp-
(1951).
THE LIQUIDUS CURVE O F T H E BINARY SYSTEM CADMIUM ACETATEPOTASSIUM ACETBTE BY ALEXANDER LEHRMAN AND DONALD SCHWEITZER Department of Chemistru, The City Colleue of New York, New York $ 1 , N . Y. Received December $9, 1963
The binary system cadmium acetate-potassium acetate was explored as part of a program' of investigating the double salts of acetates. Experimental Materials.-Analytical Reagent potassium acetate was dried in an oven a t 140" for one week before weighing. Cadmium acetate of C.r. grade to which 5-10 drops of glacial acetic acid had been added to prevent decomposition of the cadmium acetate was dried in an oven at 140' before weighing. Apparatus.-The initial crystallization temperatures were measured with a copper-constantan thermocouple of No. 24 wire in conjunction with a potentiomet,er (16-millivolt range), the cold junction being cracked ice. The e.m.f. could be read to 3Z0.02 niv. The couple was encased in a narrow guard tube that, was made by drawing out Pyrex tubing and sealing one end. I t was standardized by determining the e.m.f.'s a t the boiling point>sof water and of benzophenone, the melting points of U. S. Bureau of Standards tin and of purified potassium nitrate, and then plotting the deviations from the standard table of Adams.z A molten salt-bath was used to heat t,he mixtures. It consisted of a eutectic mixture of lithium, potassium and calcium nitrates3 contained in a tall Pyrex beaker. Method.-Definite mixtures of the salts (total weight between 25 and 35 g.) were made by weighing the components to the nearest centigram, and in some cases to 3Z3 milligrams. The mixed salts were finely ground together and placed in 2.5 X 20 cm. Pyrex test-tubes. In order to prevent decomposition of cadmium acetatme on heating, 5 drops of glacial acetic acid were added to each tube before immersing it in the hot salt-bath. The acetic acid distilled out of the mixtures during melting since the temperatures were raised to about 200". However, the mixtures rich in cadmium acetate began to decompose a t the temperatures needed for fusion, and determinat,ions on mixtures above 0.7 mole fraction of cadmium acetate could not be made. The tube containing the mixture of acetates and the couple in its guard tube was suspended in the molten nitratebath until the mixture was liquefied, and then the tube was allowed to cool slowly while stirring constantly. A beam of light was passed through the mixture, and the init,ial crystallization temperature was observed. Crossed Polaroid filters, one on each side of the tube, made the detection of the initial crystal easier. Supercooling was prevented by repeated insertions and withdrawals of a capillary glass rod into the mixture when the initial crystallization temperature was approached. When the capillary was withdrawn from the mixture the few drops clinging to it immediately solidified, and the insertion served to inoculate the melt. At least three determinations of the initial crystallization temperature of each mixture were made, or until agreement to within l owas achieved. To make sure that no breaks in the curve were overlooked, and to fix t8heeutectic temperatures, simultaneous cooling and differential cooling curves of mixtures over the range (1) For IxeviouR work see A . Lehrtnan and E. Leifet, J . A n . Chem. Soc., 60, 142 (1938); A. Lelirinan and P. Skell, ibid., 61, 3340 (1939). (2) Pyrometric Practice, U. 5. Bureau of Standards Technological Paper No. 170, p . 309. (3) A . Lelirinan. e / al.. J . Am. Chem. S o c . , 59. 170 (1037).
NOTES
384
Vol. 58
substance because it undergoes no transition in the temperature range used, and it has approximately the same heat capacity as the mixtures. Experimental Results.-Temperatures of the initial crystallization and eutectic temperatures are given in Table I and are plotted in Fig. 1.
290 275
TABLE I THESYSTEM CADMIUM ACETATE-POTASSIUM ACETATE
260
Cd(Ac0)e. Initial Eutectic mole crystallization temp., fraction temp., "C. OC.
9 245
0.000
d
,100
@ 230 H
.200 ,300 ,333 .350 .380
215 200
t-
\
0.1 0.2 0.3 0.4 0.5 0.6 Mole fraction of cadmium acetate. Fig. 1.-The liquidus curve of the binary syatem cadmium acetate-potassium acetate. 0.0 to 0.7 mole fraction of cadmium acetate were taken with separate copper-constantan thermocouples, each in conjunction with a potentiometer. The differential cooling curves were taken between tubes containing mixed acetates and a tube containing potassium acetatme,each in a hole in a single copper block that had been heated by a small resistance furnace. Potassium acetate was used as the inert
.400
.410
292 289 246 195 202 196 203 213 217
183 188
Cd(AcO)z, Initial Eutectia mole crystallization temp., fraction temp., O C . "C.
0.4286 .4444 .480 .500 .520 .550 .600 .700
22 1 216 206 210 205 202 190 220
201
187
Discussion.-The data show the existence of the double salts 2KC2H30~.Cd(CzH302)2, KC~H~OZ. Cd(C2H302)2 and 4KC2H3O2.3Cd(C2H302)2. It might be well to investigate these solid substances by crystallographic methods to see if complex ions containing cadmium and acetate groups exist. There is also a possibility of polynuclear complexes of tetra-coordinated cadmium involving acetate bridge^.^ (4) In connection with this, see I. Leden, Suensk. Kern. Tid,68, 129 (1946); W. C. Cagle and W. C. Vosburgh. J. A n . Chem. Soo., 67, 414 (1935).
