IA'DUSTRIAL A N D EA'GIA'EERING CHEMIST& Y
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200
30C
400
6W
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700
800
Figure 6-Resistivity of Clay-Corundum. Zircon Insulation
The thermal diffusivity and conductivity of a refractory predetermines the temperature a t which it will operate. A refractory having too great a thermal insulating power will not dissipate heat rapidly enough to keep it below critical temperatures. This is important in many heating appliances, and in many cases a building up of temperature in the insulation causes it to leak sufficientcurrent to add to the temperatures already existing. Thus it is that, while a porous and poorly fired clay brick may have suitable and desirable thermal insulating properties, it may be entirely unsuitable for electrical insulators for this very reason, as a result of which it soon vitrifies and, with a high electrical conductivity of the melted surface, becomes a relatively good electrical conductor. Conclusion
I n view of the foregoing, it might be well to point out the probable reasons for there being such a small amount of really fundamental data on the electrical conductivities of pure
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Temperature, C. Figure 7-Effect of B e n t o n i t e on Resist i v i t y of Zircon
ceramic compounds: there are few really pure ceramic products; the ceramic materials used vary in the quantity and kind of impurities contained; and the treatment that the materials receive may seriously alter their properties, Consequently, it would appear that the generalizations which exist will help to limit the field of considerations, but that analysis and measurements made on individual specimens will be necessary for closer discrimination. It is hoped that this paper will suggest points for consideration in the selection of suitable electrical insulation. Literature Cited (1) Bowen and Grieg, J . A m . Ceram. Soc., 7, 238 (1924). (2) Bryson, J . Soc. Glass Tech., 11, 331-46 (1927). (3) H a r t m a n n , Sullivan, and Allen, Trans. A m . Electrockem. Soc., 38, preprint (1920). (4) Henry, J. .Am. Ceram. Soc., 7, 764 (1924). (5) Rankin a n d Merwin, A m . J . Sci., 46, 301-25 (1918). (6) Suttonland~Silverman,J . A m . Ceram. Soc., 7, 86 (1922).
Freezing Points of Mixtures of Sulfuric and Nitric Acids' W. C. Holmes, G. F. Hutchison, and Barton Zieber E. I. DU PONTDE NEMOURS ASO COMPANY, WILMINGTON, DEL.
IGH-acidity mixtures of sulfuric and nitric acids are in use on a very extensive scale for nitration purposes in industry, particularly in the explosives and dye industries. For this reason a knowledge of the freezing points of such mixtures is of considerable industrial importance, since the unexpected freezing of a mixed acid in storage may be the cause of much inconvenience and delay. A further reason for knowing definitely the freezing properties and ranges of mixtures of sulfuric and nitric acids comes in the fact that, in plant operations, nitric acid is commonly added to fuming sulfuric acid in order t o lower the freezing point, since 100 per cent sulfuric acid freezes at $10" C., and 110 per cent sulfuric acid (H2SO*-S03)a t f34" C. It has been known that the addition of a small amount of nitric acid depresses the freezing point of the concentrated acid, and it
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1
Received May 21, 1931.
has sometimes been erroneously assumed that the addition of larger amounts would necessarily cause further depression. The freezing properties of mixtures of sulfuric and nitric acids of lorn-water content have already been investigated by Holmes ( 2 ) . It was found that the addition of nitric acid t o 100 per cent sulfuric acid did depress the freezing point a t first. On the addition of further amounts of nitric acid, however, a rapid rise in the freezing point occurred, until a maximum was reached. This maximum was found to exist a t the point where the acids were present in the proportion 5H2SO4-HNO3,and it was assumed that the formation of a definite chemical compound was indicated when the acids were present in the above proportions. I n this work, freezing-point determinations were made on three sets of mixtures of sulfuric and nitric acids, having total acidities of 100, 95,
I S D U S T R I A L A,VD ELVGI.VEERIAVG CHE;MIXTRY
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The method of determining the freezing point consisted, in general, in placing a 20-cc. sample of acid in a test tube, which was in turn secured in a larger test tube. The latter was immersed in the cooling medium, which was contained in a heat-insulated vessel. A standardized thermometer and stirring arrangement were also provided. The most satisfactory freezing mixture for the very low-freezing acids was found t o be solid carbon dioxide and acetone. For acids of higher freezing points, other mixtures were used, depending upon the temperature desired. The freezing point was actually determined in most cases by supercooling the acid in the test tube t o a point several degrees below the freezing point. The mixture was then inoculated with a crystal from an acid of the same composition as the one under test. The temperature rise was observed as freezing was induced, and the freezing point was taken as the highest temperature attained in this rise. After the point had been located approximately, more exact determinations were made, holding the temperature only slightly below the apparent freezing point. I t was found possible to obtain checks consistentlv, varying by not more than 0.5" C.
Correlation of Available Data
and-103 per cent, respectively, and nitric acid contents varying from 0 to 50 per cent. The solid-liquid temperature relation in the ternary system H2SO4-HNO3-H2O was subsequently investigated much more comprehensively by Carpenter and Lehrman ill). Their work covered a much wider field of acid compositions. The compound assumed by Holmes, where the anhydrous acids were present in the proport,ions represented b;y 5H,804Hx03, was found by them to he 10SO3-K2o5-9H20,both formulas requiring the qame relatiye amount,s of sulfuric and nitric acids. Experimental Work a result of the or^ of the investigators mentioned, information is available in the literature regarding the freezing points of inistures of sulfuric and nitric acids over a considerable range of compositions. No information is given, however, regarding the effect of nitric acid in small amounts on the freezing points of fuming sulfuric acids of high sulfur trioxide content. Since this range of acids is one in which such information is particularly desired because of the high freezing points of fuming acids, particularly of 109-110 per cent strength calculated as H2S04,work was carried out to determine the freezing points of acids in this area which contain varying percentages of nitric: acid. The results of the determinations made are given in Table I. Table I-Freezing-Point Determinations FREEZING H?SO; HNOi 13.0 POINT His01 HNOa H10
7;
7c
x
75
7c
7%
-8.3 -8.5 -83 -- 8 8 .. 44
+25.3 4-9.8 -9.1 + + 1188..66
96.6 104.5 102.9 10 03 4 .. 0 5 1
109 2 9 4.2 2 .. 0 1 3
-7.3 -7.4 -7.1 -- 6 6 .. 6 0
-14.0 -3.1 -21.8 -- 156.. t1
103.4 107.3 106.2 104.1 100.4 102.1 106 8 105.8 9 3 . 97 97
5 0 1.0
-8 4 -8.3 -8 3 - S8. 21 -8.1 -8 0 -7 s - 7 . 68
-12,5
102.9 102.1 101 3 19081..06 99.3 93 5 97.0
2 0 2 8 3.0 4 . 00 2 2.0 4 0 2 o
-4.9 -4.9 -4 3 - 32 . 06
-1-a '2 -11.1 - 6.9 + - 1 5. .72
-1.3
+ 6 1 -12 9
+0.5
+i.o
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c.
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1.0 3.0 4.9 2 0 2 2
+24.6 +18.9 - 2S2. . 83 -24.8 4-20.3 +i2.s - 2 1 . 18 -12
'
FREEZIKG POINT
107.5 105.5 103.6 1 10 06 6 .. 4 2
2.1 74 . 08 6.0 1.2 2 o 191.. 99
In order that a coniprehensive picture might be a t hand of the effect' of additions of nitric acid on the freezing point of sulfuric acid, all the information available in the literature was collected and tabulated. This included the results from the previous work of Holmes and of Carpenter and Lehrman, together with the data from the present investigation. Since the results of Carpenter and Lehrman are expressed in mole per cent, it was necessary to recalculate their results to per cent by weight. The data obtained are plotted in Graph 1 on triarlgular coordinates, a means which brings out relationships and effects in a striking way. Since t'riangular coordinat'es are adapted only for systems where are plotted three components which add up to 100 per cent, this was provided for by considering fuming acids to have a minus quantity of water equal to the amount that would combine with the free sulfur trioxide present. Isot'hermal lines are used to connect points representing acid compositions having the same melting points.
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Acids in this range are difficult and unpleasant to work with, and care must be taken to prevent' changes in composition, due to absorption of water.
Graph 1 shows the high points along the 0 per cent nitric acid line, corresponding approximately to the compositions H2S04-S03, HsSOd, and H?S04-H20. The location of a chemical compound a t either the composition 5H2S04HNOa or 10S03-S20j-9H20 is not shown satisfactorily. The indications are that the compound would fit in more satisfactorily on this graph a t about the composition 89 per cent sulfuric acid, 14 per cent nitric acid, 3 per cent water, though this placement is not based on anything other than iiispection of the chart. Graph 2 nil1 illustrate to one, ~ v h owishes to prevent the
INDUSTRIAL AND ENGINEERING CHEMISTRY
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freezing of fuming sulfuric acid by the addition of nitric acid, the limits that should be observed. This graph is based on the use of 93 per cent nitric acid as the source of nitric acid, and of three strengths of fuming sulfuric acid, 104.5, 107, and 109 per cent, respectively. The nitric acid plotted along the base line denotes actual per cent of 100 per cent nitric acid present. Summary
Determinations have been made of the freezing points of a number of acid mixtures containing sulfuric and nitric acid in the region where considerable free sulfur trioxide is present, the acid strengths varying between 100 and 109 per cent, calculating the sulfur trioxide present as sulfuric acid. Little information has previously been available covering this range of compositions.
Vol. 23, No. 10
All the data available in the literature and from the present work have been collected and plotted on triangular coordinates, isothermal lines being used to connect points having the same temperatures. A graph on rectangular coordinates is included, plotting the melting points of mixed acids against the nitric content. It will be noted that the most desirable nitric contents for preventing freezing are 1 per cent on the 104.5 per cent curve, 4 per cent on the 107 per cent, and 6 per cent on the 109 per cent curve. Low points occur on all three curves a t 10 per cent nitric acid. Literature Cited (1) Carpenter and Lehrman, Trans. Am. I n s f . Chem. Eng., 17, 35 (1926) (2) Holmes, J. IND.ENG.CHEJI.,12, 781 (1920).
Modification of Hypnotic Action through Changes in Chemical Structure”z Horace A. Shonle LILLYRESEARCH LABORATORIES. ELI LILI.YAND COMPAh‘Y, IXDIAXAPOLIS, I N D .
T
HERE are a number of chemical compounds which, in a
given concentration, depress the central nervous system of animals to the extent that both the normal responsiveness and the automatic activity of the living system are temporarily decreased, or even abolished. The general action of all narcotics is similar. KO definite dividing line exists between hypnotic and anesthetic effect. Larger doses of some soporifics give complete anesthesia. It is not the purpose of this article to discuss the various theories proposed to explain the action of narcotics, nor their relative merits (1, 8). There is no doubt but that the dialkyl barbituric acids will contribute in no small measure to the solution of this problem when the final chapter is written. There are various sets of physical-chemical criteria which, in the light of present knowledge, seem essential in a substance having hypnotic action. It must be remembered, however, that not all compounds falling within this classification are hypnotics. Numerous relationships of chemical structure to physiological action have been proposed, but none have stood up under the tests of experience. Chemical structure seems to affect the activity by modifying the physical-chemical properties of the compounds, although specific groups may be responsible for certain side reactions. Such diversified series of aliphatic compounds as the following exhibit sedative properties: R-OH R-CHO
K-0-CO-NHz RR’-C-CO-NH
RR’-CO R-CH( 0R’)n
NH-CO RR-C----CGXH
R-CO-NHz R-NH-CO-NHz R-CO-NH-CO-NH2
CO-NH-CO RR’-C = (S02R”)2
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1 Received July 1, 1931. Presented before the joint meeting of the Divisions of Biological, Medicinal, and Organic Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 t o April 3, 1931. 2 In this brief article, it is not possible to give credit to all the investigators whose work may be touched upon. Almost all the dialkyl barbituric acids, for which quantitative data are given, were tested in these laboratories in order that the pharmacological data would be strictly comparable.
In general, the effectiveness of this series increases with the complexity of the molecule. Since these structures have so little in common, the hypnotic action must depend on some property of the molecule as a whole and, more specifically, on its physical-chemical properties. The fact remains that hypnotic compounds almost invariably consist of lipo-soluble alkyl radicals attached to water-soluble groups, or polar groups, which are capable of forming associated molecules in aqueous solvents, and which may or may not possess similarity to shuctures occurring in the body. The only common chemical characteristic that can be ascribed to this varied group of compounds is a degree of chemical stability which prevents a too rapid destruction in the body before they exert their effect, yet permits a certain necessary degree of degradation, since compounds excreted unchanged exert little or no effect. None of these compounds have pronounced acid or basic properties. The most effective-the barbituric acids-lean toward the acid side. Thus the variations in the degree of alkalinity of the body fluids and of the cell itself must exert a more pronounced influence on this series of hypnotics than in others which lack this pseudo acid structure. Hypnotic Effect of Different Amounts of Compounds
Since degrees of sleep cannot be measured very satisfactorily in laboratory animals, the amount of the compound necessary to cause the disappearance of certain reflexes is usually used as a measure of relative hypnotic value. This value is then compared to the amount necessary to cause death. Although it may be argued that this quantitative relationship may not be a true measure of hypnotic effect, it affords a most useful, as well as the only, means of studying the effects of chemical changes in these molecules. Because the ratio of the lethal dose to the narcotic dose is larger in cold-blooded animals, warm-blooded animals must be used, if the therapeutic value of the compound is the goal. A study of the alcohols might be expected t o give relationships of the hypnotic action of the alkyl groups which might be used to advantage in preparing other series of hypnotics containing these groups. Richardson (16),over half a century ago, noted that, as the alcohols increase in molecular weight,
