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Acknowledgment The development of the application of the Grignard reagent to mineral oil deterioration is part of a joint research project of the Massachusetts Institute of Technology and the ,Utilities Co-ordinated Research, Inc. (Association of Edison Illuminating Companies), on electrical and chemical studies of insulating oil deterioration. The authors wish to acknowledge the cooperation of the Committee on Insulating Oils and Cable Saturants, U. C. R., Inc., Herman Halperin, chairman, and other committees representing the oil-refining and electrical manufacturing companies.
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The authors also wish to express their indebtedness and appreciation to J. C. Balsbaugh and J. L. Oncley for their interest and cooperation.
Literature Cited (1) Balsbaugh and Oncley, IND. ENG.CHEM.,31, 315 (1939). (2) Balsbaugh, Larsen, and Oncley, Annual Report to Utilities Coordinated Research, Ino. (Sept. 1,1937). (3) Kohler, Stone, and Fuson, J. Am. Chem. Soc., 49, 3180-7 (1927). (4) Larsen, R. G., IND. ENG.CHEM.,Anal. Ed., IO, 195 (1938). RECEIYED October 6,1938.
Improved Gas Analysis Apparatus Employing a Simplified Automatic Absorption Pipet C. M. BLAIR AND J. H. PURSE Carbide and Carbon Chemicals Corporation, South Charleston, W. Va.
I
N T H E past few years attention has been directed toward
the design of gas-absorption pipets by which the rate of absorption of gases in liquid reagents may be increased. Egerton and Pidgeon (2) described a device whereby the absorbing reagent was sprayed through the gas in the form of a fountain. This was effected by forcing the reagent through a constriction in the pipet by manually raising and lowering a reservoir of mercury connected to the pipet. An improved modification was devised by Egerton and Smith (3) but the fountain was still effected by manual operation. Later, Weydanz (7) published a description of a pipet in which a portion of reagent was trapped in a specially designed cup as the sample was introduced into the pipet. This liquid then dripped through the gas from capillary holes in the cup. The glass blowing of the pipet was involved and little saving in time was gained. The first automatic pipets were developed and in some forms patented by Huff (4). I n these forms a continually fresh surface of absorbent in contact with the gas was secured by the motion, inside the pipet, of a glass-covered iron piston actuated by an outside electromagnet. Later another mechanized gas analysis apparatus was devised by Kleiber (5) and modified by Winchester (8, 9). The complexity of this apparatus precludes its general use in gas analysis. I n the Huff electromagnetic pipets the rate of agitation is determined by the time required for the piston to fall (or rise) by gravity through the reagent. Consequently, a single standard pipet will not give optimum results with all reagents, and it is necessary to have pipets of slightly different design for the use of reagents of markedly different viscosities and specific gravities. The loose piston makes it necessary to exercise extreme care in changing solutions and in cleaning the pipets to avoid breakage. These difficulties are overcome by a pipet that is designed in the same general manner as the Huff pipet and utilizes alternating air pressure as the pumping mechanism in a way which is analogous to that described by Huff in his original patent application dated July 22, 1931. This design was not patented by Huff and does not appear to have been published elsewhere.
Apparatus The details and dimensions of the pipet are given in Figure 1. The pipet occupies approximately the same space and can be
OPENINGS PULLED OUT NOT DRILLED
P L A N OF P I P E T
lOMM.Nl
AND ELEVATION OF PIPET FIGURE 1. PLAN
"
L
ANALYTICAL EDITION
MARCH 15, 1939
167
supported in the rl/IdX9/36' AN same manner as the conventional bubbling and rod filled pipets with the exception of the space needed f o r t h e U spray-head supply tube (compare H , Figure 3) which requires a supporting member somewhat longer t h a n t h e usual commercial one. Three pieces of accessory equipment (Figure 2) are essential: a U-tube, E, partly filled with BODY LCUT-OUT QUADRANT mefcury; a threeA S SHOWN way stop-cock, C; and a push-pull air FIGURE 2. ACCESSORYEQUIPMENT pump, A , and motor C. Air cock A . Air pump B. Motor drive E. Mercury seal drive, B. As shown in Figure 3, the mercury A roller on the end of the rocker arm of the fuel pump was actuseal functions as a simple U-tube, although it is constructed with ated by a cam operated at 180 revolutions per minute by means of two concentric tubes since that form is stronger and more coma small electric motor and gear train, B. There is, however, no pact. The volume of each arm of the mercury seal is the minicritical value for the speed. mum size that will effect the transmission of the impulse to the The pump system is shown diagrammatically in Figure 3. pipet without appreciable damping. Since a satisfactory conThe diaphragm air pump, A , is actuated by the motor, B. The trol cock was not readily available, the air cock, C, was made air cock, C , is shown in the operating position. The off position from a Lunkenheimer brass drain cock [The Lunkenheimer Co., is reached by turning the cock 90' clockwise. This closes the line Cincinnati, Ohio, Catalog No. 58 (Condensed Edition) March to the air pump, making it available for use with another pipet, 1933; Figure 981, one-eighth inch brass drain cock] (6). and a t the same time vents the mercury seal, E, to the atmosA mercury seal and an air cock for each pipet were placed on a phere at opening D, thus causing the liquid in the spray-head panel that was fastened conveniently on the front of an Orsat supply tube, IZ,to return to its original level. The mercury seal apparatus. The ush pull air pump, A , was made from an also protects the metal parts of the apparatus from fumes given off A. C. Spark Plug diaphragm fuel pump (for mounting on V-8 by absorbing liquids such as fuming sulfuric acid and shields reFords) by removing the valves and strainers, plugging the inlet agents such as alkaline pyrogallol from the air. In operation the port, and loading the diaphragm with suitable spring tension. impulses from the diaphragm pump are transmitted by the mercury seal to the spray-head supply tube where the absorbing liquid is alternately pushed down and pulled up. As the liquid is pushed down, the upper check valve opens, allowing liquid to spray through the gas from spray head G. When the liquid is
80.
e
FIGURE 3. DIAGRAM OF APPARATUS A. Diaphragm push-pull air pump B . Motor drive C. Air cock, operating position D . Vent to atmosphere E. Mercury seal
F.
Automatic pipet
H. J.
Spray-head supply tube Orsat manifold
U. Spray head
K. Rubber Orsat bulb
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pulled up, the lower check valve opens, allowing fresh absorbent to flow into the spray-head supply tube. Figure 4 shows the usual Orsat gas analysis apparatus with the substitution of three automatic pipets for the conventional pipets and the addition of a push-pull air pump and a control panel which supports the mercury seals, air cocks, and a pump motor switch.
Operation The performance of an analysis with the apparatus employing the simplified automatic pipet follows the same procedure as that employed with other automatic pipets and differs from that used with the older types of apparatus in that instead of the tedious, exacting operation of running the sample into the pipet and drawing it back into the buret several times, the sample is transferred to a pipet in which it remains until absorption is complete. The absorbent is pumped through and around the gas for a predetermined length of time. During this time no watching is necessary in comparison to the ever-alert attention required with the older method to check and reverse the flow in order to avoid sending the buret confining liquid into the pipet or drawing the absorbent into the buret. While the pumping proceeds other work can be done or another gas analysis apparatus can be operated. The rate of absorption in the simplified automatic pipet is rapid. The oxygen in 100 cc. of air can be removed socompletely in 2 minutes, using alkaline pyrogallol as the absorb-
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ent, that it is unnecessary to check the reading. Because of the increased speed of absorption and also because no attention is required during absorption, reagents which heretofore have been too slow-acting for. practicable use can be employed (1). The dependability of the apparatus may be attested to by the fact that equipment is now in use with which more than 10,000 analyses have been performed. The original pump and most of the original pipets are still in use.
Acknowledgment The authors are indebted to E. I. Thomas for the design and construction of the air pump.
Literature Cited (1) Bonney and Huff, IND. ENQ.CHEM.,Anal. Ed., 9, 157 (1937). (2) Egerton, A. C., and Pidgeon, L. M., J. Sci. Instruments, 8, 234 (1931). (3) Egerton, A. C., and Smith, F. L., Ibid., 1 1 , 2 8 (1934). (4) Huff, W. J., U. S. Patent 2,094,357 (Sept. 28, 1937). (5) Kleiber, M., J . B i d . Chem., 101, 583-94 (1933). (6) Lunkenheimer Co., Cincinnati, Ohio, Catalog 58 (condensed ed.), March, 1933, Figure 981. (7) Weydana, G., Arch. Wdmnewirt., 17, 242 (1936). (8) Winchester, C. F., Rev. Sci. Instruments, 9, 134-8 (1938). (9) Winchester, C. F., Science, 78, 607-8 (1933). RECEIVED October 10, 1938.
Use of Silica Cotton in Filter Crucibles W. WALKER RUSSELL
I
AND
J. H. A. HARLEY, JR., Metcalf Laboratory, Brown University, Providence, R. I.
N SOME recent work on the determination of lead as sul-
fate it was found that silica cotton (obtained from the Owens-Illinois Glass Company, Toledo, Ohio) is an ideal material for the filtering mats in Gooch crucibles. The lead sulfate precipitate is readily retained by the silica cotton, is easily and quickly washed, and upon ignition a t 600" C. no change occurs in the silica cotton. Glass cottons sinter and become friable a t this ignition temperature, whereas silica cotton does not sinter below 800" C. Observations, were also made upon the relative merits of silica cotton, glass cottons, and asbestos with respect to chemical inertness, retentivity, and hygroscopicity. Silica is more chemically inert than the so-called resistance glasses, while asbestos may be appreciably dissolved by acids, alkalies, or alkaline solutions of phosphates. Thus in the present work it was found that a Gooch crucible plus its silica cotton mat returned to the same weight (within less than 0.05 mg.) after filtering such precipitates as lead sulfate, silver chloride, or nickel dimethylglyoxime, if the crucible was treated with the appropriate s o l v e n t i . e., 10 per cent ammonium acetate, 6 N ammonium hydroxide, or 6 N hydrochloric acid and then 95 per cent alcohol-and was faally heated again. Silica cotton possesses good,retentivity for precipitates, so that relatively thin filtering mats, weighing only about 50 mg., are required to retain any of the above-mentioned precipitates as welI as silver bromide, or cuprous thiocyanate. This appears due, a t least in part, to the fineness of the silica mm. fibers which have diameters of the order of 3 X The glass cottons examined had fiber diameters about twice this size. The very low hygroscopicity of silica cotton is a further advantage. I n this respect it proved slightly superior to glass cotton and may be much better than asbestos. I n comparative tests, similar to those of Huttig ( I ) , in which Gooch crucibles were heated to 200" C. for one hour, cooled
in a desiccator, and weighed after various intervals of atmospheric exposure, no change in weight (less than 0.03 mg.) wa8 detected in the crucible containing the silica cotton mat during 2.5 hours' exposure, while the crucible having a resistanceglass cotton mat gained 0.1 mg. in one hour, and the crucible with a mat of highly purified asbestos gained 0.1 mg. in 30 minutes. When the temperature of heating was increased to 600" C. the crucible containing the silica cotton still showed no detectable gain in weight, while the crucible containing the asbestos gained 0.1 mg. in 10 minutes' exposure. That asbestos may be much more hygroscopic is familiar to all analysts, and is recorded in Huttig's work (1) in which gains in weight of 0.1, 0.6, 1.2, 2.4, and 3.4 mg. were found for a Gooch crucible containing dried asbestos exposed to the atmosphere for 2, 5, 10, 30, and 60 minutes, respectively. A Gooch crucible is prepared with silica cotton simply by winding a narrow ribbon of the cotton into a flat spiral about 3 mm. thick and of a proper diameter to fit the bottom of the crucible. After pressing into place the cotton felts together considerably and remains in position; however, the crucible should not be carelessly handled. The weight of silica cotton used in a 20-ml. crucible is about 50 mg. Although the silica cotton is more expensive than glass cotton, little is required, and a crucible once properly prepared and intelligently handled can be used repeatedly with negligible weight changes. On the basis of the authors' present experience it appears that a Gooch crucible prepared with silica cotton has most of the advantages of a sintered-glass filter crucible, and in addition can be used a t much higher temperatures.
Literature Cited (1) G . F. Hiittig, 2. angew. Chem., 37, 48 (1924). RBCEIVED September 4, 1938.
