Vol. 70
NOTES
21s2
The Heat of Formation of Thallium Azide1 B Y IYILLIAM S M C E W A N A N D MARY h f A E WILLIAMS RECEIVED DECEVBER 1, 1953
The heat of formation of thallium azide has been determined b y explosion in a helium atmosphere and measurement of the heat evolved. There have been no thermodynamic data published on metallic azides in recent years. In 1917, LVohler and Martin2 prepared a number of aiides and fulminates and determined their "heat of detonation." Experimental details of the determinations are not given and their value of 232 cal./grani for T1N3is 7 cal./gram higher than that observed by this Laboratory. The average of five determinations made by this Laboratory is 224.8 f 0.S cal./g. Products of the decomposition of TIN3 which took place in a calorimetric bomb containing 30 atmospheres of helium are metallic thallium and of formation is in this case nitrogen. The practically the negative of the A H e of explosion. The correction, being the A H of expansion a t constant temperature of one and a half moles of nitrogen from 30 to 1 atmosphere, was computed from the expression
1x1
-
fI(TlP2)
IT[TIII,)
= ( B - TdB d T ) ( P
- PI)
where B is the second virial coefficient for nitrogen.
+
TIS1 + 3/2N:~30at,n, TI(() 3,2Si(Jozt,, 2,,o) -+ 3 2S2(iat,,, , = TlS3 TI(() 3/25>,, 240)
+
230)
kcal
AHe = -55 390 & 0 2 AH = 0 051 AHr = 4-55 34 4= 0 2
Details of the calorimetric equipment and procedure are given so t h a t the character of this work may be ascertained.
coiitains a weighed quantity of water (2000 It 0.2 g.), n itirrer, and the charged bomb. A close-fittirig lid coverI; the inner jacket, and a large double lid covers both the inner and outer calorimeter vessels. This outer lid is of hollow construction so t h a t water from t h e bath may be drawn u p into i t . T h e calorimeter is thus completely enclosed by a 1cm. air space which in turn is surrounded by a constanttemperature (=t0.002°) bath. T h e ignition wires arc attached, the stirrer is connected, and the calorimeter is allowed to sit until the change of temperature i i i t h c calorimeter with respect to time hecoincs uniform. Teinperaturc measurements :re made with ii plutiiiuiii re4staxicc thermometer using :i hIueller t>-Iic Cr-2 rciiit:iiice hrirlge. Heat transfer lxtween the calorimeter a n d the constaiit temperature bath is determined by measuring the rate of temperature chztiige before nnd after igniting the sample. Time iritervals are recorded 011 a Gaertner four-ch:iiiric,l chronograph. T h e thermal-leakage coefficient and the heat of stirring are obtained by the solution of two equations of the form dT/dt = QK IC' where dT/dt is t h e change of temperature with respect t o time in the calorimeter; Q , the thermal head, is the difference between the bath temperature and the calorimeter temperature; K is the thermal-leakage coefficient; and W is the rise in temperature produced through stirring. T h e total heat loss is obtaiiied by graphic integratioii of the teniperature-hie plot. Other corrections are made for electrical heating of t h e iron ignition wire and for the heat capacity of the re:ictaiiti and products back t o 25". T h e calorimeter was calibrated against samples of benzoic acid no. 39f supplied by the h-ational Bureau of Strtiidartls. T h e experimental data are summarized i n Table I. Preparation of Material.-Thallium azide was prepared by dissolving thallium sulfate in suficient hot water for solu tion, sodium azide was then added and the material permitted t o cool. The precipitated thallium azide was filtered, and recrystallized from n-ater, washed with alcohol and dried in a vacuum oven a t 50". T h e dried material was then pressed into 2-g. pellets in preparation for the calorimetric determination. T h e sample analysis gave 99.6470 a ~ ~ d 99.83Y0 purity in two batchei.
+
~
TABLE I EXPERIMENTAL DATA Energy equivalent of calorimeter = 2280.27 cal. Measured temp. rire, OC. 0.1977 0.1968 0.1826 Heat loss, "C. ,0011 ,0014 ,0018 - ,0036 - .Oil18 - ,0024 Stirring correction, "C 445.11 117.85 415.01 Total heat evolved, cal. 3.60 1.73 1.58 Electrical heating, cal. +2.53 -0.22 +0.79 C, reactants (25 - T I ) ,cal. -2.08 $0.73 -0.37 C, products (T2 - 25), cal. 1,9673 1 9683 1.8482 IVeight of sample, g 224.65 226.90 223.92 Heat of explosion, cal /g. H e a t of explosion ( a v . ) = 224.80 =k 0.84
+
+
Calorimetric Equipment and Procedure .-Thallium azide detonates on ignition and shatters the sample holder, therefore a n expendible porcelain crucible was used in a standard Parr, 360-ml., double valve oxygen bomb. T h e loaded bomb was twice filled with 25 atmospheres Of grade A oil-free helium and then vented t o remove any air present. It was then filled with helium t o an absolute pressure of 30 atmospheres. Helium by mass spectrographic analysis showed an oxygen content of the order of 0.003 mole per cent. If it is assumed t h a t all the oxygen present during the burning process reacts to form TL0 the heat evolved is 1.91 cal. This would result in the values given being too high by 0.95 cal./g. T h e bomb was placed in the calorimeter, consisting of ail inner and an outer metal vessel separated from each other by a I-cm. air space. The opposing vessel surfaces are chrome-plated t o reduce radiation losses. The inner jacket ~
(1) Published with t h e permissiori of t h e 'l'echniral I ) i r r c t o r , 11. Naval Ordnance T e s t Station. ( 3 ) Wohler a u d M a r t i n , Be?'., 60, 595 (1917).
S
+
0.1977 ,0017 - .0053 442 GO 1.80 $0.77 -0.29 1,9695 224.27
+
-
0.1957 , 0003
- ,0038 436.90 1.87 +0.66 -0.19 1,9419 224 26
PHYSICAL CHEMISTRY BRANCH U. S. NAVALORDXASCE TESTSTATIOS INYOKERS, CHISA LAKE,CALIFORSIA
The Formation and Dissolution of Metal Sulfides' B Y H E R B E R T A . POHL RECEIVED J U L Y 27, 19h3
The precipitation of rnetal sulfides by the action of HIS in solutions of the salts of the metals may be caused by t h e interaction of the inetnl ion wit11 S= i o i i , with the HS- ion or with molecular H2S. I t ~vvould appear froin the work described t h a t the (1) This work was done uuder C o n t r a c t #A'l'fO7..2)-1 w i t h tlir A E C : r o d i s I~iihlishpd w i t h i t s permission.
