INDUSTRIAL AND ENGINEERING CHEMISTRY
Kovember, 1928
maintenance of a constant level of juice in the carbonation tanks and of a gas of fairly constant pressure. A certain amount of latitude is possible without seriously affecting the c o n t r o l , provided the fluctuations are not too pronounded. The carbonation tanks (Figure 7) should be covered and equipped with a foam stack to prevent juice losses due to foaming. This would occur if the juice level is too high in the tank of juice being gassed, or if, for some reason, excessive foaming took place. I n view of the fact that the control of sulfitation processes, particularly of thin juice going to the evaporators, is likewise of primary importance. the behavior of the tungsten electrodes in this type of juice was also tested. An automatic control was not attempted owing to the variability in the composition and pressure of the sulfur dioxide-air mixture. The reaction of the juice was recorded, however, and the results obtained agreed very well with colorimetric and hydrogen electrode pH tests on the same material. This indicates, therefore, the possibility of utilizing similar equipment for an automatic control of sulfuring thin juice, provided arrangements are made for de-
1151
HOURS Figure 8-Facsimile of pH Record
livering sulfur dioxide under more constant conditions than are ordinarily present.
Wood Separators for Lead Storage Batteries' Relation of Life Characteristics to Cell Design C. A. Robak HORTEN, NORVAY
HEETS of wood are used to a large extent as separators in lead storage batteries, alone or together with perforated hard-rubber sheets. I n the former case the wood sheets are grooved in the direction of the grain, in the latter case smooth mood sheets are used together with ribbed hard-rubber separators, the object of the ribs being to provide some free space for the circulation of the electrolyte. In both cases it is common practice to place a flat side of the wood next to the negative and the ribs of the wood or hardrubber against the positive plates. One reason for this practice is that the oxidizing character of the positive plate material tends to destroy the wood substance and reduce the mechanical strength of the wood separators. To determine to what extent the wood separators are actually being destroyed in Q storage battery under ordinary working conditions, and particularly to make clear how great the difference is betliTeen the positive and the negative plates in this respect the following experiments were carried out,
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Description of Batteries
Two complete 42-cell batteries were built from pasted plates of the dimensions 145 X 220 X 3.5 mm., the insulation consisting of two smooth sheets of rotary-cut aspen veneer with horizontal grains which were treated with alkaline and sulfuric acid solutions to remove acetic acid and other impurities. No free space was left between the plates, the separators lying close to the surface of both the positive and the negative plates. One battery was installed in a large electric truck, the other in an electric coupe. The batteries worked fairly well. 1
Received March 23, 1928.
Charging and Discharging The truck was in use more than 300 days during a period of approximately 2 years. The battery was charged 290 times. An average of 50 per cent of the 3-hour capacity was taken out each time. The charging was carried out a t a moderate rate, 1.2 to 0.5 times the IO-hour discharge rate, but with considerable overcharging, the excess being usually 20 per cent and often more than 25 per cent of the amount discharged. The service conditions were hard. The truck wheels were provided with rings of compact rubber which on the bad roads would naturally shorten the life of the battery. The coup6 was used almost every day for nearly 3 years. This battery was charged 738 times, the ampere-hours taken out each time averaging about 25 per cent of the 3-hour capacity. The charging was usually commenced a t the 3-hour rate, the current being reduced to half or less when the point of common gassing was reached. The battery was much overcharged, the excess being usually 25 to 30 per cent and often 50 to 100 per cent of the discharge. The total distance driven was 4900 miles on bad roads in a hilly country. During all this time the separators worked well in both of the batteries and mere still in a good condition when removed for replacement of the positive plates. The separators next to the negative plates looked perfectly sound, but some of those next to the positives showed some slight signs of wear. The mechanical strength of the used separators was examined. Separators from Truck Battery Test pieces were cut along the fiber direction from the central and end parts of the separators. The pieces were
Vol. 20, No. 11
INDUSTRIAL AND ENGINEERING CHEMISTRY
1152
10 nun. wide and 150 mm. long, and the average thickness was approximately 1.2 mm. They were stored in distilled water and in wet condition subjected to a tensile strength test. The results are shown in Table I. Table I-Tensile
specimens for these determinations were cut 50 mm. wide, and those for tensile strength tests 5 mm. wide. The top, central, and bottom parts of the separators were examined separately. The results are presented in Table 11. Strength of Wood Separators after Use in Electric Coup& S-EXT TO POSITIVE PLATES &-EXT TO NEGATIVE PLATES Resistance to Resistance to Tensilea penetrationb Tensilea penetrationb Kg. per sq. mm. Kg. Kg. per sg. mm. Kg. TOP 0.538 1.254 0.755 1.517 Center 0.592 1.212 0.866 1.895 Bottom 0.575 1.152 0.851 1.645 Average 0.568 1.206 0.824 1.686 Ratio N : P-tensile, 1.45; resistance to Denetration, 1.40 a Average of 80 determinations. b Average of 35 determinations. Table 11-Mechanical
Strength of Wood Separators after Use in Truck
(Figures represent average of 55 determinations) N E X T TO POSITIVE NEXT TO iYEGATIVE PLATES(P) PLATES(N) Kg. per sq. mm. Kg. per sq. mm. End parts 0.418 0.520 Central parts 0.464 0.614 Average 0.441 0.567 1.29 Ratio N : P
Unused Separators
Comparative tests were carried out with unused separators of the same make which had been stored in slightly acidulated water. The results were: Tensile strength (25 detns.) Resistance to penetration (70 detns.)
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2 . 0 6 kg. per sq. mm. 5.96 kg.
Conclusion
Figure 1-Apparatus for Testing Separators from Coup;! Battery
Separators from Coupe Battery
Based on the experience gained on testing the first type of separators, the apparatus and conditions were improved for the tests on the coup6 battery. The apparatus shown in Figure 1 was designed for testinff the resistance of the seaaraiors to penetra6ng a hard sharp-edged object. The ;est
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A noticeable difference in mechanical strength has been found in used smooth wood separators which during use had been placed in close contact with the positive and the negative plates, respectively, in two electric traction batteries, the separators next to the negative plates showing about 30 to 45 per cent higher mechanical strength than those next to the positive plates. However, the difference is not so great as might be expected, and the destructive effect of the positive plates upon the wood substance can hardly be considered an objection to placing a flat side of a wood separator next to the positive plates if in particular cases such a design of the cell is preferable,
Automatic Control through Temperature or Pressure’ C. J. Swan2 AMERICAh.
RADIATOR COMPANY, 40 WEST 4CTH S T . , NEW YORK, N. Y.
H E increasing cost of labor, together with the keen competition which characterizes our day, has made profitable larger capital expenditures for labor-saving devices and the employment of fewer but higher paid skilled workmen. A manufacturer can no longer afford to employ labor merely to turn valves and watch the height of liquid in tanks or the degree of pressure, vacuum, or temperature on gages and dials. Twenty-five years ago there was no alternative, and cases have been known where the valve man, grown weary with the monotony of his job, was asleep when the bell rang and disastrous tank overflows resulted. Mercoid Control
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A considerable number of devices have been brought to commercial perfection within the past few years. Each has its own points of advantage. The method of control to be described here is unique in several respects, an outstanding feature being the design of the electric switch which makes and breaks contacts, depending upon changes in temperature, vacuum, or pressure. This switch consists of a glass tube, A , 1 2
Received August 21, 1928. Assistant manager, Accessories Division.
in which leads of a special material are sealed. The circuit is made or broken by a small quantity of mercury when the tube is tilted. Arcing is instantly dampened or stifled by inert gases which are hermetically sealed within the tube. Operation with safety is thus possible where there are fumes or other conditions usually hazardous. There being no oxidation or corrosion, the contact is instantaneous in operation and the contact points are permanently maintained in a clean and satisfactory condition. The control in which this switch is employed is known as the “Mercoid control.” (Figure 1) The control will carry the full-line current a t 110 or 220 volts with sufficient amperage in most cases to operate electric units up to the capacity of one horsepower. Through the use of an automatic starting switch electric units of any capacity can be operated by merely securing an across-theline starter of proper capacity. KO relay or automatic starting switch is required on loads up to 10 amperes a t 110 volts or 5 amperes a t 220 volts, as the switch will make and break the circuit across the line on loads of those amounts. The power element which operates to tilt the switch described above is a seamless, all-metal bellows, D,provided with
