INDUSTRIAL AND ENGINEERING CHEMISTRY
November, 1928
1173
Some Observations with Ultra-Accelerators1 A. D. Cummings and H. E. Simmons UNIVERSITY OF AKRON, AKROS, OHIO
LTHOUGH much has been done on accelerators, in such a vast field there is always room for additional work, particularly if, as Rhitby predicts,2 ultraaccelerators will be the main class used in course of time. This investigation was started with the following points in view: (1) to prepare several thiuram disulfides and related compounds; ( 2 ) to note their relative behavior when used as accelerators; and, if possible, deduce some explanation for the mode of action of the class or for the behavior of some particular compound, or gain additional evidence for any existing theories. The relative inactivity of thiurams derived from primary amines has been mentioned3J but no explanation published. Evidence is presented to show that decomposition of the compound into hydrogen sulfide and a mustard oil takes place so quickly a t the temperatures used that there is not time for the generation of much active accelerator. It was found that tetramethylthiuram monosulfide plus sulfur equivalent to the difference in sulfur content between it and the disulfide gave a cure in a rubber-zinc oxide mix practically equivalent to that given by the disulfide alone. This indicates that zinc dimethyldithiocarbamate may be the active accelerating agent. Romanis has noted that replacement of one of the sulfur atoms of the -CSSH group of dithio acids by an oxygen atom destroys the accelerating power. The action of carbon oxydfide on diethylamine gave a compound whose zinc salt did act as an accelerator in a rubber-sulfur-zinc oxide mix; but it was very slow, showing that the above observation is applicable also to the carbamates. Oxidation of the diethylamine-diethylmonothiocarbamateyielded an oil which decomposed so readily that it seemed unnecessary to test it as an accelerator. KO analysis was made, but the decomposition products indicated that the compound was the one desired-namely,
A
(CzHs)dC=O
This consists in treating an ice-cooled alcoholic solution of 2 mols amine and 1 mol carbon disulfide with an alcoholic solution of 1 mol iodine to oxidize the intermediate dithiocarbamate. The disulfide separates soon or on addition of ice water. This procedure was followed exactly in the preparation of the tetramethyl, dimethyldiethyl, and dimethylthiurams. In the case of the tetraethyl and dimethyldiphenyl compounds the separation of the thiuram can be hastened by warming the mixture after the iodine has been added. The dimethyldiphenylthiuram disulfide was rather impure at first and was recrystallized from a mixture of alcohol and chloroform. The oxidizing agent used throughout these experiments was a saturated alcoholic solution of iodine, which proved to be very convenient as well as to give good results, although R ~ m a n i referring ,~ to tetramethylthiuram disulfide, states that the quickest way is to pass chlorine through an aqueous solution of the corresponding dithiocarbamate. No reference to a thiuram made from an amine containing two different alkyl groups was found in the literature. Consequently, one was prepared from methylethylamine in order to yield symmetrical dimethyldiethylthiuram disulfide:
Determination of sulfur showed 47.62 per cent (theoretical 47.78 per cent). Tetramethylthiuram monosulfide was made from the disulfide by warming with potassium cyanide in dilute alco1101.7
Zinc salts of the dithiocarbamates were obtained by treatment of the carbamates in solution with zinc acetate. To test the effect of a -COSH group, carbon oxysulfide, prepared from ammonium thiocyanate and sulfuric a ~ i d , ~ ~ ~ ~ ’ ~ was passed through a cold alcoholic solution of diethylamine.
I
s I
M e l t i n g P o i n t s of T h i u r a m s P r e p a r e d
RZCORDED
FOUND P R E ~ I O U S L Y
S
Curing experiments were carried out with the thiuram disulfides and dithiocarbamates. The compounds derived from an ethylamine seem to be a little more rapid in bringing about maximum tensile strength. With the rubber used, increase in tensile attributable to the effect of the accelerator amounts to about 100 per cent. The accelerator also speeds up aging to some extent, but this can be easily overcome by the use of a small quantity of antioxidant. Preparation of Compounds I n the preparation of all thiuram disulfides the method given by Braun6 was followed generally, such modifications in temperature control as seemed advisable being introduced. 1 Presented before t h e Division of Rubber Chemistry a t t h e 75th Meeting of t h e American Chemical Society, St. Louis, Mo., April 16 t o 19, 1928 * I K D . E N G CHEM., 16, 1005 (1923). a Romani, Gwrn. chsm. i n d . applicola. 5, 197 (1921); C. A., 16, 864 (1922). 4 Twiss, Brazier. and Thomas, J . SOC.Chem. I n d , 41,81T (1922). 6 Caoutchouc. 19, 11626 (1922); C.A . , 17, 901 (1923). 6 B e y . , 36, 817 (1902).
Tetramethylthiuram disulfide Tetrapthylthiurani disulfide Dimethvlthiiiram disulfide Dirnrth; Idiph?nplthiiirum disulfide Dirrierh?.ldirth!.lrhiurani d i s L l f i d e
Tctr~rneth,.ltliiiirnin monosulfide
1 4 6 O C. 69.5-70 101 5-102 192
i.? 103-106
1466
706 102’ 156’
...
1067
Dimethylthiuram Disulfide Inactive When milled into rubber in the same relative proportion as the other thiurams, the dimethylthiuram disulfide showed almost no activity, whereas the tetramethyl derivative exhibited high accelerating power. This observation is similar to that made by R ~ m a n iT, ~~ i s sand , ~ others. Twiss states that the easy conversion of the dithiocarbamates of primary amines into mustard oils of unpleasant odor has been given as an objection to their use, and says, “The dialkylamine derivatives are likely to prove preferable on more weighty grounds; they are clearly much more effective.” The lack of activity in the corresponding thiurams also “indicates a fundamental difference between the behavior of the primary Braun and Stechele, Be?., 36, 2275 (1903). Beilstein, I. p. 877. 9 Fischer, Biochem. Z , 126, 12 (1921); C.A , , 16, 964 (1922). 10 Schmidt, B e y . , 10, 191 (1877). 7 8
INDUSTRIAL AND ENGINEERING CHEMISTRY
1174
and secondary amine derivatives.” One would naturally make the deduction that the lack of activity and easy decomposition might be closely connected. Dimethylthiuram disulfide was heated on the steam bath and in an air bath, alone; mixed with sulfur and zinc oxide; and mixed with sulfur, zinc oxide, and rubber. In all cases hydrogen sulfide and mustard oil vapors were evolved. Hence it can be concluded the reaction CH3NHC=S
1 +S + H S + 2CHsN:CS
CH~NHLS Dimethylthiuram disulfide methyl isothiocyanate
+sulfur
+ hydrogen sulfide +
Table I-Curing Data: Basic Mix Plus 1/1200 Mol Thiuram Disulfide !A) Tetramethylthiuram disulfide ( C ) Dimethyldiethylthiuram disulfide (B) Tetraethylthiuram disulfide ( D ) Dimethvldi~henvlthiuramdisulfide F--(D)Lbs./ K2.< zn.2 cm. 231 16.2 770 54.1 3230 2 2 6 . 7 720% 2325 163.45
200 14.05 64a 45.3 3330 2 3 3 . 7 760% 2530 1 7 7 . 6
257 18.05 956 67.1 3910 2 7 5 . 0 725% 2835 1 9 8 . 5
214 15.02 734 51.6 3610 2 6 4 . 0 750% 2710 1 9 0 . 5
T.4 Ts TB EB
296 20.8 1013 7 1 . 2 3040 2 1 3 . 5 672% 2045 1 4 3 . 8
276 19.4 902 63.3 3684 2 5 8 . 5 709% 2610 1 8 3 . 5
T3
294 20.6 1025 7 2 . 0 6 3363 2 3 6 . 5 690% 2320 1 6 3 . 0
245 17.3 965 67.8 3630 2 5 5 . 0 702% 2025 142.36
T.P.
I S 1
RzNC=S
I S
+ HzS + ZnO+
163 11.4 727 51.1 3600 2 5 3 . 1 730% 2630 1 8 4 . 5
238 16.7 824 57.8 3190 2 2 4 . 0 712% 2270 1 5 9 . 5
+ H ~ O+ s
‘zn
S/
I
RzNC=S RzNC=S Thiuram disulfide hydrogen sulfide zinc oxide + zinc dialkyl dithiocarbamate water sulfur (R2N-CS-ShZn HzS-+-R~NCS-S-NHZRZ CS?+ZnS Zinc salt hydrogen sulfide +amine salt carbon disulfide zinc sulfide RcN-C=S
+
proceeds so rapidly that there is very little chance for any cyclical set of changes activating the sulfur and regenerating the activating agent to take place before the thiuram is all destroyed by the irreversible decomposition.ll Furthermore, after standing several weeks the thiuram no longer showed a melting point of 102” C. This was anticipated from the fact that it decomposed on the steam bath. It began to decompose and finally liquefied a t about 95” C. Also, a piece of lead acetate paper suspended in the container showed unmistakable evidence of hydrogen sulfide in half an hour a t room temperature.
T3
R,NC=S
I
S
T5 TB EB
the amine to prevent the escape of the latter. In view of the high accelerating power of the disulfide, the second reaction must preponderate, at least in the curing mold. The following summary, given by Bedford and his co-workers, shows the reactions possible:
S
I
Vol. 20, No. 11
+
+ +
+ +
+
+
+
I
+ ZnO +Ss>Zn + 2R2h” + H 2 0
~R~XC-S-NHZRZ
It
I
S
R2N--C=S Amine salt zinc oxide +zinc salt amine water 2RzNH 2CSz ZnO + (R2N-CS-S)zZn HtO Amine carbon disulfide zinc oxide +zinc salt water
++
+
+
+
+
+ +
+
Research having in view isolation of reaction products of the accelerators during vulcanization should throw much light on the mode of action of these bodies. Thiuramdisulfide us. Monosulfide Plus Sulfur
It is well known that tetramethylthiuram disulfide will cure without sulfur quite readily, whereas the corresponding monosulfide will cure only very slowly under similar conditions. Two batches were made up as follows: . FORMULA I Rubber Zinc oxide Disulfide
FORMULA I1 200 10 10
Rubber Zinc oxide Monosulfide Sulfur
200 10 8.666 1.334
36-MINUTE CURE
Ts TS
Ta EB T.P.
175 12.3 863 60.6 3650 2 5 6 . 1 717% 2615 1 8 4 . 0
240 16.9 840 59.0 3288 2 3 2 . 5 709% 2335 1 6 4 . 0
4C-MINUTE CURE
T.P.
261 18.35 1095 77.0 3490 2 4 5 . 0 675% 2350 1 6 5 . 2
287 20.2 975 68.5 3285 2 3 0 . 5 690 7 0 2270 1 5 9 . 5
46-MINUTE CURE
Ts TB EB T.P.
283 19.9 1067 75.0 3367 2 3 6 . 5 679% 2290 1 6 1 . 0
When tetramethylthiuram disulfide is heated with rubber, sulfur, and zinc oxide in an air bath, no hydrogen sulfide is evolved at first, but the vapors are alkaline. Soon, as the temperature rises, hydrogen sulfide begins to escape and the alkalinity increases. After a short time the alkaline vapors cease. The presence of these vapors is easily explained by the mechanism suggested by Bedford and SebrellI2 and Bedford and Gray13 for the action of zinc oxide and hydrogen sulfide, coming from the union of rubber and sulfur, on thiuram disulfides. The fact that the alkaline vapors do not continue may be explained either by supposing that the thiuram has all reacted or decomposed and hence does not generate any more amine (or other alkaline product), or that the carbon disulfide formed reacts rapidly enough with I * Compare Twiss and Thomas, J . SOC.Chem. I n d . , 42, 899T (1923), referring to xanthates. 12 J. I N D . E N D . CHEM, 14, 25 (1922) 18 I b i d . . 16, 720 (1923).
The sulfur used in I1 is equivalent to the difference in sulfur content between monosulfide and disulfide. A 1-hour cure of these mixes was too soft to remove from the mold. Substantially equal cures were obtained from both mixes in 2, 3 , 4 , and 5 hours at 115’ C., indicating that in curing with the monosulfide, sulfur, and zinc oxide the same substance is formed as is produced from zinc oxide and the disulfide, this substance in turn being the active agent in promoting vulcanization. This substance would be expected to be zinc dimethyldithiocarbamate, thus adding another bit of evidence to the contention of Bedford and others that the zinc salts are the active agents in causing acceleration when using dithiocarbamates or thiuram disulfides. I n one trial monosulfide was heated in an open crucible with sulfur and with sulfur and zinc oxide. No substances having the melting point of tetramethylthiuram disulfide or zinc dimethyldithiocarbamate were obtained. While this does not confirm the above hypothesis concerning the behavior of monosulfide with sulfur and zinc oxide, it does not in any way disprove it. Monothiocarbamates and Their Oxidation Products
When carbonyl sulfide was passed into diethylamine well cooled in a mixture of ice and salt, a solid was formed which is in all probability diethylamine-diethylmonothiocarbamate. A portion of this was dissolved in water and treated with iodine. When no more iodine was taken up, the resulting liquid was evaporated with a current of air, yielding an oil. Another portion in water solution gave a sticky precipitate when zinc acetate was added. This precipitate was dried and found to have some accelerating power, l / ~ mmol (assum-
IiVD USTRIAL AiVD ENGINEERISG CHEMISTRY
November 1928
ing it to be zinc diethylmonothiocarbamate) producing a cure in 4 hours a t 115' C. in the standard mix used throughout this work. More of the oil mentioned above was prepared and extracted with ether. The aqueous layer yielded diethylammonium iodide. The ether was allowed t o evaporate and the oil left several weeks a t room temperature. AFter a few days some sulfur separated out accompanied by a slight evolution of hydrogen sulfide. This continued steadily but slowly. Addition of concentrated hydrochloric acid gave much hydrogen sulfide and sulfur. Boiling and subsequent neutralization of the acid solution showed the presence of diethyl amine. The mechanism of the spontaneous decomposition may be represented as follows:
1175
corresponding thiuram disulfides which were investigated. Before many definite conclusions are drawn regarding the accelerating value of the uramine disulfides, however, more work should be done; but the above is a possible explanation of the fact that replacing one sulfur atom in the -CSSH group by oxygen removes the activity as an accelerator. Table 11-Curing Data: Basic Mix Plus 1/1200 Mol Dithiocarbamate (E) Zinc dimethyldithiocarbamate (F) Zinc diethyldithiocarbamate (E)---(F)--Lbs lin.1 Kg./cm.2 Lbs.jin.2 Kg.1cm.l
-___
-___
?I-MINUTE CCRE
226 15.8 818 57.5 3510 247.0 711 R 2490 175.0
l'3
Z'5
TB
E5
(GHs)dVC=O
T.P.
(C?H,)zN
I
I c=o
S
I
---f
S
(Ci")iN
I
30-MINUTE CURE
+ cos + s
19.6 279 914 64.2 3090 217.0 6745; 2085 146.5
7-d
T5 TB E5 T.P. T3
+ H20 +COS + HsS
COS
288 935 3190
r5
TB
Es T P.
In the presence of hydrocliloric acid the reactions proceed rapidly and further:
2160
TB E5 T.P.
+ HjO --+ 2(C2Ha\2NH+ CO?
I
S
I + 2H30 +2(C?H0)2SH+ 2C02 + HIS + S s
I ( C2Ho)zNk==0
+-
Tetraethyl uramine disulfide water --+ diethyl amine carbon dioxide hydrogen sulfide
+
+
+ sulfur
This oil was not tested as an accelerator, but since it is unstable a t room temperature, decomposition would probably prevent it from showing much power. With zinc oxide it should form a salt equivalent in activity to the zinc salt prepared. This salt shows decomposition without melting, which is not true of any of the zinc dialkyldithiocarbamates or the BEFOREAGIXG Kg( Cm.
--I DAYLbsi/ Kg.! cm. rn. (-4)
T.P.
19.3 275 64.3 914 242 3440 70070 169 2410
24.7 351 97 0 1380 249 59 3550 670% 167 2380
Ta TI TB
1 4 . 0 5 200 58.00 825 204 2910
23.3 332 103.69 1476 220 3135 640% 140.62 2001
(B)
EB T.P.
EB
137 668?945 6.8 15.7 99.7
1150
TZ T5 TB EB T.P.
13.6 54.50 256.62
777
cm.
25.1 357 92.5 1317 164 5 2340 588% 96 66 1375
T3
209 780 234.5 3340 722% 169.0 2410
23.8
139.2
194
3650
197. :68"310
14.7
54.7
7-5
D A Y 5 7
"E.( cm.
Lbs./ in.2
7 - 6 DAYSLbsi/ Kg;/ cm. sn.
-7
13 9
9.6 137 200% 1.92 27.35
K2.L cm.
DAYSLbs;/
rn.
11.7_- 167 115%
2 06
29 3
198
250y0
3.48
49.5
339
79.4_-2130 41 J / O 37.8 538
23.4 334 295% 6.82 98.6 9.48
135
53.4 760 475% 361
2z.4 SAME A S
18.7 266 20.8 1009 1 2 8 . 5 1830 576y0 73.82 1051
20.3 289 82.8 1178 88.2 1255 526% 46.3 659
21.7 309 87.5 1245 287.5 4090 727% 209.12 2975
21.4 305 90.7 1290 266.62 3650 6957, 178.5 2540
(A)
(A)
9.26
132
1.79
25.6
1905b
BASIC MIX CURED I50 MINUTES AT 141'
(E)
EB
132 0
BASIC MIX P L U S 1/1ZDO MOL ZINC D I ~ l E T H Y L D I T H I O C 4 R B A M A T E
(D)
T.P.
668Yc
BASIC MIX PLUS 1/1?00 MOL T E T R A 3 l E T H P L T H I U R . ~ ~DISULFIDE l
810%
80.85
TB
1880
The rubber used for all curing experiments was a good grade of ribbed smoked sheet which had been previously masticated in 100-pound lots on an gO-inch mill. The basic mix consisted of rubber 100, zinc oxide 5 , sulfur 10, and gave a maximum tensile of 126.5 grams per sq. cm. (1800 lbs. per sq. in.) To this was added mol of ultra-acce!erator. The rubber was broken down for 15 minutes on a 12-inch (30cm.) experimental mill cooling the rolls with a slow stream of water. The compounding ingredients mere added and milling was completed in 5 minutes. Curing was done in a two-platen press rvhose temperature was checked by a Bristo1 recording thermometer which had been standardized against a mercury thermometer placed between the platens. The mold had two chromium-plated cavities approximately 0.1 inch (2.5 mm.) deep and of sufficient size to a1lo.u
Table 111-Aging Data -3 DAYS--. -4 DAYS-. Kg./ Lbs./ K g . / Lbs./ in.? on.' in.2 cm.2 in.2
96.7 224 1420
T.P.
Ts
151 8
G64Sb
7 2 DAYSKg.! Lbs./
(C)
Ta T6 TB
18.9 69 0 197 0
Curing Experiments
( C*HO)2JC=O
EB
269 982 2810
20.5 69.4 209.5
1980
(CzH5)lN
T.,
6i7c;
292 988 2980
7-3
2'5
making the complete decomposition:
T6 TB
20 2 65 6 224 0
168.74
40-41INUTE CURE
(C?HshN
I I
19.3 62 3 237.0
35-MINUTE CURE
(C,HS)PNL=O (the oil)
C=O
275 886 3370,12y0 2400
17.0
14.6 208 212y0 3 09 44.0
C
242
393 27.6 370c/, 10.2 145.5
11.4 163 337% 3.88 55.2
BUT R U N PARALLEL TVITH ( E )
11.3 176 205% 2.54 36.2
13.6 194 2255 3.65 43.7
11.2 160 195% 2.19 31.2
P L U S 1 PART ANTIOXIDANT
25.2 99.7
149.0.
359 1420 2120
KJO%
81.4
1167
21.8 310 91.90 1300 1 5 5 . 6 2215 5757" 89.63 1275
23.6 336 100.2 1428 1 6 5 . 8 2360 580% 96.4 1370
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 BATTERYCOMPANY,
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
+
