THE DIELECTRIC COSSTaAATS O F THE HAU,OGE:S HYDRIDES BY 0SC.XR C. S C H l E F E R . I S D HERRI.\N SCHLUSDT I
This communication ii a continuation of the earlier vork of Schlundt on the dielectric constants of pure solventi Thc \-alues for the halogen hydrides-hydrogen iodide h>drogen bromide, and hydrogen chloride-in the liquid itate, are noxy added, arid the value of solid hydrogen cyanide i b included, the dielectric constant of the liquid hal-inq been published some >-ears ago. The dielectric capacity of the halogen hydrides 15 of interest at this time in connection 11 ith the researches of Steele, JIcIntosh, and AArchibaldLon the phJ-sical constant\, iolvent, and ionizing poner of these cornpounds The subsequent 11 o r k of ,Archibald3 revealed the fact that t!iese sols-enti T icld excellent conducting 5olutions 11 ith iei-eral organic acids and alcohols On the basis of the Sernst-Thomion rule, t h a t a close parallelism esisti betneen ioninng pon er and dielectiic capacitJ-, one [rould be inclined to a55iqn medium or high x d u e s t o the dielectric constants of theye solvents The results obtained, however, show that the halogen h ~ d r i d e s fall in the class of solvents haT-ing Ion dielectric capacity of which ether and chloroform ma>- he taken as examples Pi eparatzoiz o j Compoziizds.-In the preparation of the Yydrides studied, stress was laid on securing pure samples of the compounds in the liquid state. The final measurements TT ere conducted with samples t h a t had been redistilled. Precautions were taken t o exclude moisture, and some of the measurements \iere repeated because traces of water were detected in the samples used. In this connection we found t h a t samples known to contain a small quantity of water gave Jour Phys C h e m , 5 , 1 5 7 , j03 (1901) 8, I Z ? (1904) Phil Trans , 205A, 99 (1906) Jour - h i Chem SOC, 29, 6 6 j , 1416 (1907)
670
Oscar C. Schaejer and Herman Schlundt
values for the dielectric constant t h a t exceeded those of the pure solvents by only about I percent-a difference almost within the limits of measurement. In the case of hydrogen chloride, a sample containing water in small quantity, when cooled in a bath of solid carbon dioxide and ether, SOT shows minute, white flakes of ice or a hydrate. Evidently the solubility of ice in liquid hydrogen chloride i5 very limited a t low temperatures. TT-e also noted that traces of bromine in liquid hydrogen bromide, or iodine in liquid hydrogen iodide, cause practically no change in the value of the dielectric constant. Liquid hydrogen iodide \vas prepared by dropping water from a tap funnel on a warmed mixture of red phosphorus (one part) and iodine (ten parts) contained in a generating flask supplied with a manometer tube dipping into mercurj7. The es-olved gas was passed through a series of large L-tubestwo containing glass beads moistened with concentrated hydriodic acid, and two containing fused calcium chloride, before it was condensed in a small receiver cooled in a bath of solid carbon dioxide and ether contained in a Dewar tube. The outlet tube of the receiver was protected from atmospheric moisture by a calcium chloride tube which was in series with a water suction pump. The whole apparatus was exhausted to a pressure of 2 cm before the generation of the hydrogen iodide was started. The condensed product was generally colored by a trace of iodine. X colorless sample was obtained by distilling the liquid again and condensing the vapor directly in the measuring cells. Finally the arms of the cells were sealed off in a small flame a t constricted points. For the preparation of liquid hydrogen bromide, an apparatus similar t o the one just described was charged with moistened red phosphorus, and bromine mas added from the drop funnel. Bromine vapors were removed by passing the gas through a U tube charged with moist red phosphorus, and a second tube containing glass beads moistened with concentrated hydrobromic acid. The condersed liquid was further purified by distillation.
The Dielectvic C o n s t a n t s o j the H a l o g e n Hydrides
671
To liquefy hydrogen chloride, the temperature of Thilorier's mixture was reduced to -100' C. by evaporating the carbon dioxide under low pressure. Hydrogen chloride was generated by allowing concentrated sulphuric acid t o drip on common salt in the usual form of apparatus. The gas was dried by passing it through concentrated sulphuric acid and calcium chloride, and the liquid was finally redistilled. -~leasuvenzeizts.-The dielectric constants were determined with the well known apparatus devised by Drude. The improved apparatus of Schmidt? was used. -4s the measurements were extended t o room temperatures, special forms of cells had t o be constructed for confining the liquids. By fusing a side tube on to the usual form, a t a point close t o the bulb, a very sen-iceable cell was obtained. *Another form consisted of a small C tube, slightly widened a t the bend where the platinum plates were sealed in. The cells were calibrated with the standard solutions of acetone and benzene recommended by Drude. &Itleast two independent determinations were conducted with different samples of each of the liquids in cells whose dielectric capacity differed somewhat. DIELECTRICCOSST.4STs O F HALOGES HYDRIDES Substa ti ce
Hydrogen Hydrogen Hydrogen Hydrogen Hydrogen Hydrogen Hydrogen Hydrogen Hydrogen
iodide iodide iodide (solid) bromide bromide chloride chloride cyanide (solid) cyanide (solid)
D.
c.
Temperature
2.90
2.88 3 95 3.82 6.29 4.60 8.8j 2.4 3.05
21
Temperature coefficient
7
-50
-j 0 24.7
-80 27
7
-90 -2
j
-70
Further details of preparation and figures of the apparatus used are given by Oscar C Schaefer in his thesis for the degree of Bachelor of Science, University of 1\Iissouri, June, 1909. Drude's Ann., g, 919 (1902).
672
Oscar C . Schaejer and H e m a n Schlundt
Results.-The values given for the dielectric constants in the table, unless otherwise indicated, refer to the substances in the liquid state under their own vapor pressure a t the temperature given. Comparing the \-slues obtained a t room temperatures, it is seen that the dielectric constants increase with decrease in molecular weight. Hydrogen iodide excepted, the temperature coefficients are negative. Hydrogen iodide s h o m an increase in dielectric capacitl- upon solidification. H>-drogen cyanide. on the other hand, shows a great fall, the \ - d u e in the liquid state being about 100. The dielectric capacity of the halogen hydrides is Ion. in comparison with sol\-ents that possess marked ionizing power, such as water, formic acid, the nitriles, and liquid sulphur dioxide. Their marked ionizing p o n w is therefore somewhat anomalous. lynless \\-e a S S U t l i c ahnormallj- high x-dues for the mobilities of the ions in the solutions of the halogen liydrides that .-irctiibaltl' found to be excellent electrolytes, ~1-eare forced to t h e conclusion that other factors besides the dielectric constant must lie considercd in estimating the ionizing poiver of solvent.;. i ' h < , l ) l im 1
1,cic. cit
1-11 h,.(1 ti',
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