INDUSTRIAL A N D ENGINEERING CHEMISTRY
1176
four dumb-bell test pieces to be cut from each slab. The die used had a constriction 2 inches long and 0.25 inch (6 mm.) wide. Tensile tests were made on a Scott vertical tester equipped with a recording device. I n the accompanying tables, the ultimate tensile strength is represented by TB, the load at an elongation of x00 per cent by Tx,and the elongation at break by EB. T. P. indicates the tensile product ( E B x TB)/1000. While no striking differences between these accelerators are shown, those derived from an ethylamine appear to be somewhat more rapid.4 Among the thiuram disulfides there is a distinct tendency toward discontinuity of vulcanization even with the 5 parts zinc oxide. Had longer cures been made with the dithiocarbamates, doubtless the same effect, would have been 0 b ~ e r v e d . l ~The dithiocarbamates are more rapid than the corresponding thiurams.
Vol. 20, No. 11
initial results with tetramethylthiuram disulfide showed such very poor aging qualities that it seemed advisable to compare the behavior of the basic mix even though the curing had to be done a t a higher temperature. The aging qualities of the rubber used are evidently very poor, but nevertheless the accelerator speeds up the effect of aging some. All the accelerated samples except (D) show distinct after-curing. There is also a discontinuity of aging noticeable. This may have no meaning, being due simply to a slight lack of uniformity in the test pieces; but since it occurs in every case among the accelerated stocks, it is more probable that it may represent a change in state of aggregation of the rubber or in some other factors affecting vulcanization. The same factor which causes discontinuity of vulcanization may bring about this effect during aging. The efficiency of the antioxidant is great.
Aging
Acknowledgment
The aging tests were carried out in an electric oven at 70" After removing from the Oven, strips were to remain a t about 20" C. for 24 hours before testing. The
The authors wish to express their gratitude to members of the Chemistry Department of the University of Akron for their help and to R. p. Dinsmore and L, B, Sebrell, of the Goodgear Tire and Rubber Comsanv, for and suggestions on the organization of this' paper.
'
14
Twiss, J . SOC.Chem. Ind., 40,242T (1921).
Effect of Hydrogen-Ion Concentration on the Voltage of the LeClanche Dry Cell' Berthel M. Thompson FRENCH BATTERYC O M P A N Y ,
M A D I S O N , WIS.
The voltage of a mixture of manganese dioxide and RT = N F loge graphite is a straight-line function of t h e pH of t h e contains a carbon rod it is in contact. The slope of t h e solution with which surrounded by a wet C tetrnvilent manganese ions line in the case of the natural ores approximates -0.059, m i x t u r e of graphite, manC tri,.nlentmsoglmeaeiooa X COEt h e value predicted from theoretical considerations. -0.059 log COH- = ganese dioxide, and ammoArtificially prepared manganese dioxide in some cases, -0.059 pH constant nium chloride. This core is at least, gives a steeper slope. The measurements are where E = voltage, R = gas surrounded by a water-starch constant, T = absolute ternof significance in connection with t h e behavior of t h e paste containing zinc chloride perature, N = valence, F = LeClanche dry cell. snd ammonium chloride and Faraday (96,500 coulombs). the whole is contained in a The equation was found to apply satisfactorily to an cylindrical zinc can, which serves also as the negative electrode. The voltage of the cell depends on the potential of the zinc electrode of manganese dioxide deposited on a platinum wire electrode against the zinc ions in the cell and on the potential of by electrolysis, and it was the object of the present investithe inert graphite electrode which is surrounded by hydrogen gation to test the application of the theory under conditions and hydroxyl ions and various oxidizing and reducing ions. actually present in the LeClanche dry cell. It was found that As the cell is discharged, ammonia is liberated, the cell be- the equation applies equally well to a mixture of manganese comes alkaline, and the voltage falls. It has been found that dioxide ore and graphite when proper precautions are taken most of the loss of voltage occurs at the graphite electrode and to obtain the true pH of the solution actually in contact with that the potential of the zinc electrode falls only a few hun- the particles of graphite. dredths of a volt. Experimental Procedure Holler and Ritehie* concluded that the potential of an elecDry mixtures were made containing approximately 3 trode composed of a mixture of graphite and some manganese ores is a logarithmic function of the hydrogen-ion concen- parts of mangapese dioxide and 1 part of natural graphite tration, but that the potential of a similar electrode containing together with small crystals of ammonium chloride. The a chemically prepared oxide is independent of the hydrogen- graphite was carefully purified by digestion with concentrated hydrochloric acid until only a trace of iron remained. The ion concentration. According to D a n i e l ~ ,the ~ core of the dry cell should manganese dioxide was ground so that most of it passed a function as a manganese dioxide electrode and its potential 65-mesh sieve. The material was thoroughly screened and then wet in should give a straight line having a slope of about - 0.059 when separate lots with different buffer solutions of saturated am, plotted against the pH of the solution. monium chloride containing hydrochloric acid, zinc chloride, The equation on which this prediction was made is or ammonium hydroxide. Cores were made of the wet ma1 Received April 25, 1928. 2.54 cm. in diameter and 4.1 cm. high, and a long carterial 2 Bur. Standards, Sci. Paper 864 (1920). bon pencil was inserted. They were wrapped in cheesecloth, :Trans. Am. Eltcltochem. Soc., 68 (1928)
HE LeClanche dry cell
T
+
IAVD USTRIAL AND ENGINEERING CHE.I!fISTRY
November, 1928
paraffined on the top and bottom, and placed with the buffer solutions in tall cylindrical zinc cans (3.2 by 8.6 em.) which had been thoroughly insulated with asphalt on the inside. The cans were sealed with melted paraffin and only the tops of the carbon pencils protruded above the seal. The cans were placed in a thermostat a t 25” C. for a t least 48 hours, after which the voltage had become constant. A hole was drilled through the paraffin and a normal KC1 salt bridge in agar-agar was inserted in the mixture and connected with a normal calomel electrode. The potentiometer (Type K Leeds & Northrup) was connected to the carbon pencil and the calomel electrode. The determination of the true p H of the solution was not easy. The problem was solved by squeezing out the solution with a hydraulic press, after it had come to equilibrium with the manganese dioxide and graphite, and measuring its pH with a hydrogen electrode. A hole just large enough to hold a zinc can 3.2 cm. in diameter was bored through a block of steel. A short disk was fitted into the bottom of the hole and a core of manganese dioxide and graphite was inserted in the zinc can and placed in the steel block. The cores were inserted in the press just after the voltage readings had been taken. A plunger of steel was inserted and a pressure from 5 to 13 tons was applied with a hydraulic press. The plunger and can were heavily coated with asphalt to prevent a short circuit, and as the core was compressed the solution which it contained was squeezed up between the zinc container and the plunger. It was aspirated off into a small tube and its pH was determined quickly with a small hydrogen electrode. It was proved that no appreciable error was introduced by loss of ammonia during the determination. Results
I n Table I the data are recorded for a Montana ore, a Caucasian ore, and an artificial manganese dioxide. The voltages are referred to the normal calomel electrode as zero. Table I-Voltages
of Manganese Dioxide a n d Graphite Mixtures a t Varying pH
MONTANA MnOt
CATJCASIAN MnOz
pH
Voltage
pH
Voltage
pH
0.6025 0.6026
0.6025
5.17 5.24 5.20
0.5216 0.5226 0.5221
4.71 4.97 4.84
0.7349 0.7380 0.i365
4.49 4.82 4.65
0.5536 0.5628 0.6532
6.56 6.46 6.51
0.4734 0.4746 0.4740
6*12
Av.
0.6798 0.6801 0.6800
6.03 6.03 6.03
Av.
0.5033 0.4978 0.5000
6.78 6.72 6.75
0.3816 0.3813 0.3815
6.99 6.99
0.5874 0.5881 0.5878
6.21 6.47 6.34
0.3827 Av.
0.3830
8.50 8.56 8.53
0.2674 0.2708 0.2690
8.33 8.33
0.3110 0.3095 0.3102
8.54 8.46 8.50
9.36 9.55 9.45
0.2009 0.1994 0.2002
9.96 9.96
Av.
0.3833
0.2022 0.1992
0.2007
Av.
* Electrode
6.12
*
*
placed contained sufficient reserve alkalinity and acidity to retain their original pH. After standing for 48 hours with cores of manganese dioxide and graphite, the supernatant liquid was poured off and its pH was determined with a hy.8
1
40 50 60 A-Montana MnOz B-Caucasian hInOz
9.96
became poisoned.
Duplicate experiments are given in each case to indicate the order of accuracy obtained. In the pH readings marked by an asterisk (*) the hydrogen electrode became poisoned. Below a pH of 4.5 the hydrogen electrode became poisoned by the solution which had been in contact with the manganese dioxide ore, but solutions more acid than 4.5 are unimportant because they never occur in the LeClanche dry cell. The data are shown graphically in Figure 1. Curve A , representing Montana manganese dioxide, has a slope of -0.07; curve B, representing Caucasian manganese dioxide, has a slope of -0.07; and curve C, representing the artificial manganese dioxide, has a slope of -0.10, In preliminary experiments it was assumed that the buffer solutions in which the manganese dioxide and graphite were
70
80
90
100
11.0
C-Artificial MnOz D-MnOz electroplated on platin u m wire
Figure 1-Influence of pH of t h e Solution o n t h e Voltage of a Mixture of Manganese Dioxide a n d Graphite
drogen electrode. The voltage-pH curves were quite different from the final results shown in Figure 1, for the voltage remained nearly constant from a pH of 2 t o a pH of 6. The results were not significant, however, for the pH of the original solution had been changed by contact with the manganese dioxide and graphite. Measurements on the solution squeezed out of the core with a hydraulic press showed that the alkaline solutions became less alkaline and the acid solutions became less acid.
ARTIFICIALMnOz
Voltage
1177
Conclusions
Figure 1 shows that mixtures of manganese dioxide and graphite give straight lines when the voltage (referred to the normal calomel electrode) is plotted against the pH of the solution and in the case of natural ores the slope of the lines is -0.07. These facts support the theory of the LeClanche dry cell, recently proposed by D a n i e l ~ . ~According to this theory the depolarizing action of the manganese dioxide is due to tetravalent manganese ions which bathe the network of graphite particles which constitutes the positive electrode. The dotted line, D, was obtained by electroplating manganese dioxide on a platinum wire.4 The fact that lines B and D are nearly identical supports the theory that the graphite particles as well as the platinum wire are merely inert electrodes and play no part in the reaction.* The fact that the slopes are not exactly -0.059, as predicted by theory, may be explained on the basis that other oxidizing or reducing ions in addition to the tetravalent and trivalent manganese ions, are present as impurities. Ferrous and ferric ions or divalent manganese ions may change the slope. The higher voltages of the Montana manganese dioxide can probably be attributed also to the presence of other ions, particularly oxidizing ions. A comparison between the results of this investigation and those of Holler and Ritchie2 is interesting. These authors concluded that “the potential of an electrode composed of a mixture of graphite and some manganese ores is a logarithmic function of the hydrogen-ion concentration of the solution in contact with the electrodes.” This statement is in 4
Line D is taken from reference 3, Figure 1
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INDUSTRIAL AND ENGINEERIXG CHEMISTRY
Vol. 20, No. 11
agreement with the results given above that the voltage is tion agree with the results of this investigation. The imdirectly proportional to the pH of the solution. Taking the proved technic described here, in which the pH of the solution difference in voltage between their most acid and their most is obtained under equilibrium conditions, shows that the basic solutions, these authors found an average change of straight-line relation is maintained over the whole range in-0.067 volt for each pH with Caucasian manganese dioxide. vestigated. The check between this 70.067 and the - 0.07 of the present Holler and Ritchie found that in alkaline solutions the investigation is not so satisfactory as it seems a t first, however, voltage of the manganese dioxide and graphite increased on because when all the results of Holler and Ritchie are plotted standing. while in acid solutions the voltage decreased. This in the manner of Figure 1 a curve is obtained with some parts fact is readily explained by the findings of the present research deviating greatly from the straight line. In fact, the voltage that an acid solution becomes less acid in contact with manis nearly constant over the range from a pH of 2 to a pH of 6. ganese dioxide and graphite and an alkaline solution becomes The same results were obtained also by Martin and Hel- less alkaline. The voltage of the graphite-manganese dioxide f r e ~ h twho , ~ plotted the voltage of the manganese dioxide and electrode depends on the pH of the solution actually in congraphite mixture against the pH of the original solution, as tact with the graphite particles, and hydrogen ions are taken up by hydrated manganese dioxide or by impurities of cardetermined with a quinhydrone electrode. These results are very similar to the preliminary results bonate which may be present in the ore, thereby decreasing mentioned earlier in this communication, in which the pH of the acidity and decreasing the voltage. On the alkaline side the solution did not represent the true pH of the solution the voltage is increased because ammonia and hydroxyl ions actually in contact with the particles of manganese dioxide are absorbed from the solution. Artificial manganese dioxides vary greatly in their properand graphite. The reason for the abnormal behavior is obvious. I n the ties, depending on their method of preparation. Holler and solutions between a pH of 2 and a pH of 6 the amount of acid Ritchie reported an artificial manganese dioxide which gave is so small that it is readily taken up by the large quantity practically no difference in voltage a t the different pH’s. of manganese dioxide. With large quantities of hydrochloric I n the present investigation the voltage measurements of an acid or ammonium hydroxide the buffer capacity of the solu- artificial manganese dioxide plotted against the pH of the tions is increased to a point where the effect of the manganese solution gave a straight line and its slope was abnormally dioxide is minimized, and the pH of the solution in contact steep. The artificial product was somewhat finer than the with the manganese dioxide is more nearly equal to that of natural ores, but this fact is probably not important. The the original solution, In the more alkaline solutions the re- steeper slope may be due to ions other than tetravalent and sults of Holler and Ritchie using the pH of the original solu- trivalent manganese ions, which are present as impurities in the artificial manganese dioxide. 5 Trans. A m . Electrochem. Soc., 63 (1928).
Indene and Styrene-Crude Materials in Industrial Quantities’ Ralph L. Brown PITTSBURGH EXPERIXENT STATION, U. S. BUREAU OF MINES, PITTSBURGH, PA.
H E chemistry of indene has recently been well reviewed by Courtot,2 and as indicated by him has been much studied from a theoretical point of view. Because of its occurrence in the oils and tar obtained by the distillation of coal, indene, which occurs along with coumarone in the solvent-naphtha fraction, has been much studied by the chemists of that industry, and consequently it has appeared prominently in industrial chemical literature and patent records. This is largely due to the properties which permit of the manufacture from it of a resin usable in varnishes, paints, cements, and many other product^.^ Its use in the production of perfumes, dyes, and possibly medicines has been predicted by Courtot. It has previously been pointed out that indene is a constituent of carbureted water gas and may be found in its tar4 and in the oily condensate which collects in mains in which carbureted water gas is being distributed.6 Because of its possible industrial uses and in the interest of the dis-
T
1 Received May 17, 1928. Published by permission of the Director, U. S. Bureau of Mines. (Not subject to copyright.) 2 R e p . gln. s c i . , 84,607 (1923). 8 A comprehensive compilation of literature, patents, and uses m a y be found in Chapters 2 and 3 of “Synthetic Resins and Their Plastics” (1923). by Ellis. 4 Brown and Howard, IND.ENG. CHEY.,16, 1147 (1923). 6 Brown, Am. Gas Assocn. Monthly, 4, 435 (1922); Am. Gas Assocn., Tech. Sect., 4, 280 (1922).
semination of knowledge, this paper presents the results of some quantitative studies of carbureted water-gas condensate. The analyses are entirely typical and pay particular attention to the indene and styrene content of the oils. Although it has a large literature of theoretical studies, the existence of styrene as a constituent of carbureted watergas tar, carbureted water-gas light oil, and “holder oil,” and its occurrence in industrial quantities was first pointed out only a few years ago.6-6 Except for the incidental references, no quantitative figures have been published on the styrene potentially available for industrial uses. These uses might be in the form of synthetic chemical derivatives or possibly in the field of plastics, and the data to be presented are therefore considered potentially valuable to the public and industrialist alike. These data were taken in 1922 as basic to a research on gummy deposits in gas meters. The presence of styrene in the oils obtained by the distillation of coal and those produced in the carburetion of water gas has not been sufficiently appreciated industrially. The presence of styrene in crude motor benzene and its property of polymerizing to give gum (resin in solution) and resin (metastyrene and higher polymers) are in part the reasons why the upper boiling limit of refined motor benzene is fixed 0
7
8
Brown, Am. Gas. Assocn., Tech. Sect., 6, 1353-1406 (1924). Brown and Berger, IND. ENG.CHBM.,16, 917 (1924); 17, 168 (1925). Brown, I b i d . . 17, 920 (1925).
*
