INDUSTRIAL AND ENGINEERING
March 15, 1934
TABLE11. OPTIMUM TEMPERATURES GRAD^
TEMPBRATURE O
c.
1
810
2
800
3
4
790 780
Small variations in porosity inevitably occur between individual disks of the same lot, but properly made disks of any one grade invariably differ In porosity from all disks of another grade. Grade 1 is suitable for a rapid filter for coarse precipitates, and is especially adapted to use as a gas bubbler where gases must be scrubbed rapidly. It has been found useful in constructing exCractors to retain the solid nonextractives. Grade 4 retained the finest analytical precipitates. Grades 2 and 3 are intermediate in porosity, and are to be recommended for: separating analytical precipitates which are not of the very finest varieties, since their speed of filtration is decidedly greater than that of grade 4. Likewise they are suitable for gas bubblers where the volume of absorbent is not large and the gas must be very thoroughly scrubbed in one vessel, as in the quantitative absorption of carbon dioxide in a small volume of alkaline solution. No difficulties have been met in duplicating porosities at various times when the same glass and sintering procedure are used. All sizes of disks which the authors have made have been successfully sealed into Pyrex tubing. No difficulty has been encountered in the seal itself, but an annular crack in the tube frequently formed at the edge of the smaller sizes of disk on
CHEMISTRY
155
cooling. This difficulty was in no case avoided by annealing with a large flame of any temperature, but could be avoided by sealing the disk into a tapered rather than a straight tube, or better, by using a very fine hot flame to anneal the edge of the seal after partial cooling. The strain is localized at the edge of the seal by contraction of the disk on cooling and the only satisfactory form of annealing is a local application of heat at the point of strain without a reheating of the disk itself. Turning the tube in a lathe and applying pressure at the seal with a carbon rod produced the best seals with a minimum of fusion of the disk. By this procedure the micro external filters described by Kirk (9) have been made satisfactorily, though no filters of this small size have been available hitherto. The authors have used the method of Shatenshtein (4) in a few instances. It is successful in sintering Pyrex glass when the size of filter made is small-not over 1 cm. in diameterand when the glass used is relatively coarse-grades 1 or %but the method has very limited application and lacks accurate control and reproducibility. LITERATURE CITED (1) Bruce, W. F., and Bent, H. E., J . Am. Chem. SOC.,5 3 , 9 9 0 (1931). (2) Kirk, P. L., Mikrochem., 14, 1 (1933). (3) Prausnitz, P. H., IR'D. ENG.CHEM.,Anal. Ed., 4, 430 (1932). (4) Shatenshtein, A. E., J . Chem. Ind. (Moscow), 6, 1800 (1929). (5) Thomas, M. D., IND.ENG.CHEM.,Anal. Ed., 5, 193 (1933).
RBCEIWDOctober 31, 1933. Prepared with the aid of a grant from the Reaearoh Board of the University of California
A Si:mple Radio Relay Circuit G. B. HEISIGAND D. C. GERNES,School of Chemistry, University of Minnesota, Minneapolis, Minn.
R
AD10 circuits are used in controlling the temperature of both high- and low-temperature thermostats, in the intermittent starting and stopping of motor sets, and in amplifying the current from a photoelectric cell to accomplish these or similar purposes. The advantage of a radio type of relay circuit over that ordinarily used is that, because of the small current in the grid circuit no arcing can take place to foul or disintegrate the contacts. Furthermore, the circuit may be made and broken in an atmosphere containing inflammable vapors (1-6),, The principle involved is, that the application of an appropriate voltage (very low amperage is required) to the grid of a suitable radio tube will cause a large decrease in the current flowing in the plate circuit. By having the current in the plate circuit operate a relay, very large currents can be made or broken by appropriate contacts. The circuits ordinarily described require direct current, and in some cases both direct and alternating current. Since direct current is rarely available, storage or dry cells (B or C batteries) must be used. These are an additional expense and frequently become discharged a t a most inopportune time. The writers have adapted B standard single amplifying circuit, which requires only alternating current, for general use in the laboratory. The simplicity of the circuit is immediately apparent from Figure 1. A is a 171-A power tube which will furnish a plate circuit of approximately 10 milliamperes. B is a device for closing the grid circuit. It may be a thermal regulator of the usual mercury type or one made from a bimetallic strip, or it may be a photoelectric cell. C is a fixed condenser used to smooth out the intermittent direct plate current and L is the source
platinum contacts, while 178BY h a s several. Relay 22A is a large i n s t r u ment used in communication lines , a n d h a s b u t one
4 -= C
B
-T-R2
T
ANALYTICAL EDITION
156
Vol. 6, No. 2
nected to the contact points of the relay. Relay 178BY can readily be adapted to operate the vacuum control. TABLEI. 'SUITABLE RESISTANCES KIND RELAY RI RI Watt8 Watt8 B69 60 60 60 60 60 50 178BY 60 200-ohm variable 25 resistor 22A 60 100 60 50 60 60
OF
LAMP 01 Mf. Carbon 1 Carbon 1 Mazda 1 Carbon 2 Maids, 2 Carbon l o r 2 Masda l o r 2 Carbon 1 or2
to be made by a mechanism driven by a synchronous motor. An electric clock may be readily converted to a timer by placing contacts on the clock face and closing the circuit through the large hand. If an apparatus is to be started or APPROXIMAT^ RESIBTANCEMINIMUM stopped a t a given time, the contacts may be made closed PLATE OF OPBRATINQ through both hands of the clock. Other possibilities for the CURRENT RELAY CURRENT use of the circuit will be suggested by the problems in the Milliamveres Ohm8 Milliamweres 2.4' 12,000 1.0 immediate field of the worker. 1.1
2.6 8.5 9.1 6.0 4.0
2000
8.0
100
4.0
This circuit may be used in connection with a photoelectric cell, P. J. 23. The terminals of the cells are connected in the grid circuit a t B. On being illuminated, sufficient potential is applied to the circuit to produce enough current in the plate circuit to operate the relay. In order to have the relay operate accurately a t regular intervals, the grid circuit may be closed by causing a contact
ACENOWLEDGMENT Acknowledgment is made to R. S. Allison for pertinent suggestions. LITERATURE CITED (1) Adams, J. Optical SOC.Am., 8 , 599 (1924). (2) Andrews, J . Franklin Inst., 206,285-99 (1928). (3) Beattie and Jacobus, J. Phys. Chem., 34,1264 (1930). (4) Cameron, D., private communication. (5) Scott and Brickwedde, Bur. Standards J . Research, 6,401 (1931). RECEIVED August 22, 1933.
Automatic Vacuum Regulator GEORGEF. LIEBIG,JR., University of California Citrus Experiment Station, Riverside, Calif.
I
N LABORATORIES having a vacuum supply there is often a need for some device to reduce the degree of
vacuum and a t the same time maintain it a t the desired degree. A vacuum regulator was accordingly designed, similar in principle to that used in commercial regulators, which oDerates satisfactorilv and can be constructed by anyone from ordinary materials, " The dimensions as given in J Figure 1 need not be rigidly followed and can be modified to fit available materials. The body, L, of the regulator is a wide-mouthed glass bottle,
the bottom of which has been cut off a n d t h e s h a r p edges smoothed by rubbing with emery cloth. A r u b b e r disk, A , i s cut out of an ordinary No. 14 solid rubber stopper, the proper section being selected so that the diameter of A is slightly larger than the inside d i a m e t e r of L, thus' affording a snug air-tight fit when A is placed in position in L. A 0.19-inch (0.47-cm.) brass rod, B, with a brass washer, C, soldered on as indicated and a small loop of wire soldered on one end, is inserted in a 0.125-inch (0.32-om.) hole which has been cut in the center of disk A . A section of 0.125-inch heavy-walled rubber pressure tubing T, with ends cut smooth and perpendicular t o the hole, is slipped on the lower end of rod B. A sheet of No. 16 Stubs gage LO (approximately 1.7 mm.) copper is formed i n t o a cylinder, D, and slipped into place as shown. L The function of this cylinder is FIGURE 1. DIAGRAM OF t o keep the edges of disk A in VACUUMREGULATOR position when suction is applied on the lower side of A in chamber 0. Disk A with'parts B and T attached is then ut into tion. A well-rolled cork, M , holding two pieces orglass ut% l$
7
E and El, is inserted in the neck of the bottle, and El with up er end carefully fire-polished, is adjusted so that it just toucges rubber section T. Two circular disks of wood, G, are glued to ether and a hole is bored in the center a trifle larger in diameter &an the glass tube, K. K is 2 mm. less in length than the distance between the to of disk A and wooden cover G. The purpose of K is to keep disE A from being pulled completely out of position by spring F when there is no reduction of pressure in chamber 0. A square sheet of copper, H , with corners turned down, and a hole in the center to accommodate threaded brass rod J and knurled knob I , is centered over the hole in the cover G. A loop of wire is soldered on the end of J , and spring F , which is made by winding 16 turns of No. 18 B. & S. gage steel piano wire around a 0.25-inch (0.64-cm.) rod, is put in position. With a spring such as F it is possible to vary the degree of vacuum between 1 and 7 inches (2.54 and 17.8 cm.) of mercury. With a stronger spring the range can be extended to the maximum of the vacuum supply. The operation of the regulator is as follows: With the regulator connected to the vacuum supply and apparatus, knob I is turned, placing tension on spring F, which pulls disk A upward in the center, causing rubber section T to be pulled away from tube E , allowing chamber 0 and connected apparatus to be evacuated. When the pull of spring F is balanced by the pressure of the air on the top of disk A , rubber section T is pressed against tube E and held there until the degree of vacuum in chamber 0 falls off, when spring F again pulls T away from E. Thus the degree of vacuum is automatically maintained fairly constant in the connected apparatus. The operator by increasing or decreasing the tension of spring F can cause a corresponding increase or decrease in the degree of vacuum. A regulator as described has been used very successfully in reducing a line vacuum of 26 inches (66 cm.) of mercury to just a few inches for suction filtering. RECEIVED October, 3, 1933.
DOLOMITIC LIMESTONE, or dolomite, added to complete fertilizers that are acid-forming in their influence on the soil will prevent them from increasing soil acidity, according t o the findings of two U. S. Department of Agriculture chemists, K. C. Beeson and Wm. H. Ross of the Bureau of Chemistry and Soils. This observation is considered especially important for the South where much fertilizer is used.
