(22) Mair, B. J., Schicktanz, S. T., Znd. Eng. Chem. 28, 1446 (1936). (23) Mair, B. J., Willingham, C. B., Streiff, A. J., J. Research Natl. Bur. Standards 21, 581 (1938). (24) Martin, C. C., Sankin, -4., ANAL. CHEY.25, 206 (1953). (25) Melpolder, F. W., Brown, R. A., Washall, T. A., Doherty, W., Headington, C. E., Ibid., 28, 1936 (1956). (26) Miron, S., Zbid., 27, 1917 (1955). (27) Nes, K. van, “Chemist;ry of Petroleum Hydrocarbons, Chap. 16, Vol. 1, Reinhold, Nen- York, 1954. (28) Nes, K. van, Westen, H. A. van, “Aspects of the Constitution of Mineral Oils,” Elsevier, New York, 1951. (29) OTeiIl, J., “Applied Mass Spectrometry,” pp. 27-46, Report of Conference, Institute of Petroleum, London, 1954.
(30) Rossini, F. D., Mair, B. J., Streiff, A. J.,,,“Hydrocarbons from Petroleum, Reinhold, New York, 1954. (31) Rossini, F. D., Pitzer, K. S., Arnett, R. L., Braun, R. M., Pimental, G. C., “Selected Values of Physical and Thermodynamic Properties of
Hydrocarbons,” Carnegie Press, Pittsburgh, 1953. (32) Schiessler, R. W., Clarke, D. G., Rowland, C. S., Slatman, W. S., Herr, C. H., Proc. Am. Petrol. Inst. 24 (111), 73 (1943). (33) Schiessler, R. W., Herr, C. H., Rytina, A. W., Weisel, C. A., Fischl, F., McLaughlin, R. L., Keuhner. H. H.. Zbid.., 26., (111) \ I
254 (1946).
(34) . , Schiessler. R. W.. Whitmore. F. C.. Znd. Eng. Chem. 47, 1660 (i955). ’ (35) . . Simha, R., Hadden, S. T., J . Chem. Phyk 25, 702 (1956). ‘ (36) Smith, E. E., Eng. Expt. Station,
Ohio State University, Columbus, Ohio, Bull. 152, 1953. Stout, W. J., King, R. W., Peterkin, M. E., Kurtz, S.S., Jr., Am. SOC. Testing Materials, Spec. Tech. Publ. 224, in press. Tadema, H. J., in “Aspects of the Constitution of Mineral Oils,” by van Nes and van Westen, pp. 250, 317, 318, Elsevier. New York. (39) Weinstock, K. V., Storey E. B., Sweely, J. S., Znd. Eng. &hem. 45, 1035 (1953). RECEIVEDfor review June 18, 1957. hccepted March 13, 1958. Division of
Petroleum Chemistry, Symposium on Polynuclear Hydrocarbons, 130th Meeting, ACS, Atlantic City, N. J., September 1956. Complete tables of API42 data may be purchased from the American Documentation Institute, Library of Congress, lT7ashington, D. C., as AD1 4597.
Portable, Automatic Alarm for Detection of Toxic Agents in Atmosphere J. C. YOUNG Chemical Warfare laboratories, Army Chemical Center, Md.
J. R. PARSONS and H. E. REEBER Radio Corp. o f America, Camden, N. J. ,Because the G series of chemical warfare gases (nerve gases) give no sensory warning of their presence, an automatic alarm was developed which will give warning of sublethal dosages o f these agents. The alarm i s portable, weighs about 25 pounds, will operate automatically for 12 hours, will detect 0.02 p.p.m. of GB (isopropyl methyl phosphonofluoridate) within 2 minutes, and will alarm to concentrations above 2 p.p.m. in 5 seconds. It i s believed that this instrument has broad industrial application, in that any single phase colorimetric test for atmospheric polutants can be adapted to the unit.
A
of World War 11, the Germans were found to possess chemical warfare agents which offered no sensory means of detection. These gases, the G-agents or nerve gases, are far more toxic than any other known war agent. I n 1953 the Chemical Corps established a project for the development of a portable automatic alarm which would detect sublethal dosages of G-agents in the field. Because this unit was designed for operation by troops in combat, very stringent military requirements were established to govern the final design. The alarm developed will operate T THE CLOSE
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ANALYTICAL CHEMISTRY
Table I. Alarm Reliability
Agent Concn. (GB), P.P.M.
KO.of Tests
0.01 0.02 0.10 2.00 5.00 100
50 200 50 50 20 5
a
% response
4v. Alarm Time 5 min. 2 min. 1 min. 5 sec. 5 sec. 5 see.
Response,“
%
58 98 100 100 100 100
=
No. of times alarm occurred in av. alarm time X 100 No. of tests
without attention for 12 hours. It will detect concentrations of GB (isopropyl methyl phosphonofluoridate) as low as 0.02 p.p.m. within 2 minutes and will alarm to higher concentrations (2 p.p.m.) in 5 seconds (see Table I). The unit (Figures 1 and 2) is 17 inches high, l Y / 4 inches wide, fi3/4 inches deep, and weighs 24 pounds complete. It operates from the standard 24volt direct current source used for Army vehicle operation or, because the alarm requires only 19-matt power for operation, it can be operated from a portable power supply. The alarm should have broad application to industrial air pollution problems. Because the detecting system
consists of a chemical solution and plain a-cellulose paper tape, numerous other chemical systems may be substituted for the reagents now used to detect G-agents-e.g., Patty-Petty reagent Fas used in the alarm and concentrations as low as 2.5 p.p.m. of nitrogen dioxide were easily detectable. Using benzidine-type compounds, as little as 1.5 p.p.m. of chlorine was detected. Using other oxidizable amines, as little as 0.02 p.p.m. of ozone was easily detected. It is believed that other simple tests for compounds such as hydrogen sulfide, sulfur dioxide, ammonia, hydrochloric acid and sulfuric acid may be developed. The absorption wave length or color of the compound formed for the detection medium is not critical because the unit does not contain optical filters. The alarm mechanism depends on the amount of total reflected light reduction caused by the colored compound and not of any specific wave length absorption. OVER-ALL OPERATION
The alarm is based upon the red color formed when any G-agent comes into contact with a combined solution of dianisidine (3,3’-dimethoxybenzidine) and sodium pyrophosphate peroxide. An air pump in the alarm samples outside air through a paper prefilter,
which removes particulate matter, and then through an rr-cellulose tape. A fresh portion of the tape is wetted every 5 minutes with the combined solution of
from a source to t a o phototubes. One phototube monitors the tape under the sampling port. The output from this tube is balanced out against the output from the other phototube which acts as a reference and monitors the wetted tape through which no air is passed. If any red color develops on the sample spot from G-agent, less light reaches the sample phototube and an unbalance occurs in the electronic circuit. This triggers both an audible and a visual alarm by means of relays. CHEMICAL SYSTEM
Extreme difficulty was encountered in obtaining a chemical system with the required sensitivity and stahiMy. The system had to possess extreme sensitivity to G-agents--e.g., 0.02 p.p.m. of GB-and yet be stahle enough for prolonged operation in an atmosphere contaminated with various gases occurring in the field under combat conditions. The system also bad to be stahle under field climatic conditions, and the chemicals themselves bad to withstand tropical and arctic storage for a 6-month period. The reaction chosen is the Schoenemann reaction which occurs between an alkaline peroxide solution and a Gagent in the presence of a heneidinetype compound to give a highly colored dye ( I , 2). Background data indicated that the reaction n.as the most sensitive one for G-agents and was also fairly selective and free from chemical interference. A great increase in sensitivity was obtained hy using paper tape rather than solutions as the collection medium. Development of the alarm was simplified
Front view, without cover
in that a continuous flow of solution was unnecessary. It also simplified the solution pumping &em and the solution storage system. Because of the extreme sensitivity of the reaction, the electronic system itself could he made relatively insensitive, while still retaining adequate sensitivity to nerve gas. The detection or alarm level was set so that a 30% change in total light was required to cause an alarm, thus increasing the stability of the electronics-e.g., small fluctuations in current would not affect the alarm. The chemical reagents used in the alarm are o-dianisidiue dihydrochloride and sodium pyrophosphate peroxide. The dihydrochloride salt of o-dianisidine is far more stahle in storage than its base, and it easily converts to o-dianisidine in alkaline medium. Considerable n-ork was done to find a suitable oxidant for the reaction. To simplify the solution pumping and storage systems, an oxidant that would coexist with the dianisidine in one solution was selected. Sodium pyrophosphate peroxide was chosen because it acts as a buffer a t pH 9 which is the optimum pH for the reaction. It forma a stable combined solution n-it,h dianisidine for 24-hour periods at elevated temperatures. Chemical interference tests were conducted on the reaction, both in the field and in the laboratory. As shown in Table 11, the only interfering compounds-i.e., compounds giving a false response or reducing the sensitivity of the reaction-of those tested were nitrogen dioxide, chlorine, and chlorosulfonic acid screening smoke. The concentrations of these compounds, hovever, were much higher than can normally be expected in the field. Moreover, these concentrations mere high enough to cause toxic or hazardous effects in themselves, so that a false response was not undesirable.
Table II. Compounds Tested for Possible Interference Material Response Red smoke (SO,) None None Green smoke (SO,) Purple smoke (SO,) None Yellow smoke (SO,) None None Black smoke (SO,) FT mix (XgO, COS, None nn,
\VKf.,O,, Mg flare (MgO) Incendiary Kapalm (ALO,) Oil smoke (hydro. . carbon) Smokeless powder
None None None None None
None None None None
gaaes Nitrogen dioxide (lab test) (NO,) Chlorine (lab test) (CL)
Inhibited agent None False alarm (5 7 / liter) False alarm (undetermined concn. j
MECHANICAL SYSTEM
A minimum of electrical power is required for the mechanical operation of the alarm. This is achieved by operating all mechanical features of the alarm from two motors. A timing motor operates the paper changer and the solution pump by means of an eccentric cam. As the timer rotates, energy is slowly stored up in two springs. When a follower rod drops on the eccentric cam, a ratchet becomes engaged and one spring rotates t h e paper changing mechanism. Just prior to the drop of the follower on the cam two microswitches are engaged; one shuts the electronic circuit off and the other operates a solenoid which breaks
Figure 2. E21 alarm Rear view, without cover YOL. 30, NO. 7, JULY 195
the air seal on the paper tape so that the tape is free to slide through the sampling head. The paper tape is wetted about 30 seconds before the paper advances by means of a follower arm. The arm is disengaged from the solution pump piston plate by means of a stop. The second spring then pulls the pistons forward and the tape is wetted. The second motor operates the air pump which is a positive displacement piston-type pump with ball check valves. The liquid knockout pot removes excess solution drawn off the paper tape before it reaches the pump cylinder. Total electrical power for mechanical operation is 7 watts. Five watts are used for the air pump motor, and 2 watts are required to operate the timing motor. One of the most interesting mechanical problems that arose in the development was obtaining a suitable air sampling pump. Initial experiments with low power air blowers proved that impingement of sampled gases was not feasible from a sensitivity standpoint. An effort was then made to obtain a low operating power air pump that would operate under the relatively large head caused by drawing the sampled gases through the test paper. No commercially available air pumps met these requirements. The first unit that was developed used an eccentric rotor that revolved a t 1800 r.p.m. This system had the necessary air flow, but because of the high friction inherent in the unit required 30 watts for operation. A second pump was constructed using an electrical vibrator and a speaker as a pump diaphragm. The vibrator operated a t 2000 cycles per second and had a life of only 12 hours. This pump, similar in design to a commercial pump which operated on the vibration of a rubber diaphragm, was not satisfactory owing to wear of the diaphragm and to poor regulation of the oscillation mechanism. The next design has proved satisfactory; it is a piston-type pump operating from an internally geared motor revolving a t 500 r.p.m. The pump requires 5 watts for operation and will move 1.5 liters of air per minute against a head of 12 cm. of mercury. (At the present time, this pump is not commercially available; however, blueprints of the unit may be obtained from the Department of Commerce.) An air seal is maintained by use of an O-ring between the piston and the cylinder wall. Simple spring, ball check valves control the air flow and the only maintenance required is cleaning the balls and occasionally lubricating the piston. Each revolution of the motor evacuates about 7 cc. of air when the pump is operating against zero head. To remove excess solution which is drawn off the wet tape by the air
1238
ANALYTICAL CHEMIGTRY
passing through the paper, a knockout pot was installed immediately in front of the air pump. It is necessary to remove this solution from the air sampling stream because the reagents crystallize from the solution on the ball check valves and destroy their airsealing ability. A great deal of effort was required to construct a reliable, yet simple mechanism for moving the combined test solution from its storage compartment to the paper tape. A system that required little power and yet gave consistently uniform wetting was necessary. The first liquid pump developed was a roller squeeze pump which pumped solutions by means of an eccentric roller which periodically constricted Tygon and forced liquid ahead. This unit was not satisfactory because of its high power requirements and lack of uniform wetting caused by air-bubble formation in the line. A wick system of wetting also proved unsatisfactory because of color formation on the wick and paper from sampled air oxidation of the dianisidine. Frequent clogging of the wick after 6 hours of operation also occurred. An atomizer system of wetting was discarded because of its poor regulation and difficulty of operation, Several types of gravity feed systems proved unsuccessful owing to clogging of the exit port by dianisidine on prolonged operation. The system finally developed and used successfully consists of a hypodermic syringe-type pump actuated by an arm attached to the paper changing mechanism. The pump is extremely simple; it consists of a cylinder, a barrel to push the liquid, a guide, and a spring. The seal between the barrel and cylinder is effected by means of an O-ring. The unit contains no valving and is self-priming. The paper-changing mechanism which operates off the timing motor is simple in operation. Two drive wheels are necessary because the tear strength of the wet paper tape is extremely low. One wheel pushes the paper and the other, which is connected to the first by a chain drive, pulls the tape. A tension roller which rests against the pull wheel winds up the used tape. ELECTRONIC OPERATION
The unit employs a direct current photometric circuit which is essentially sensitive only to the difference in illumination of two photosensitive detectors, while remaining insensitive to the absolute level of the illumination, This feature permits stable operation of the device with variations in the surface texture of the paper, and in the degree of wetting of the paper. The circuit is symmetric about each of the photocells and is designed with several negative feedback loops in each of the photocell amplifiers for improved stability.
The voltage drops developed across the photocell load resistors are amplified by 26A6 voltage amplifiers having common degeneration in their cathode circuits. The outputs of these amplifiers are fed to two 26A6 triode-connected tubes arranged as a cathodecoupled difference amplifier. The metering and alarm circuits are sensitive to differences in potential of the two cathodes of the difference-amplifiers. In the alarm, when the potential difference is enough to produce a current of 100 pa. through 4000 ohms, an alarm is sounded. The unit will operate over the range of voltage from 22 to 28 volts direct current and withstand sudden source voltage fluctuations as mould occur in vehicular operation. The instrument will not operate from a direct current supply which has more than 3% alternating current ripple voltage. OPTICS
A small low wattage flashlight bulb serves as light source. To obtain enough light a t low wattage a General Electric 40 light is used and operated a t 7.5 volts, which is 1.5 volts higher than recommended. The overvoltage operation greatly reduces the life of the bulbs because tungsten is deposited on the glass envelope and the tungsten reduces the light output markedly. However, this bulb was the best of over 30 bulbs that were tested. Work is still in progress to obtain a longer life light source. Because the red colored compound formed by the Schoenemann reaction has a wide absorption band ranging from 350 to about 600 mp with no sharp absorption peaks, optical filters are not used in the unit. Furthermore, all available light from the source is required for electronic operation, and filters are undesirable because any of the sharper cutoff types reduce the available light appreciably. The over-all path length from light source to paper tape to photocells has been kept as short as possible, the over-all distance being less than 1 inch. OPERATION AT CLIMATIC EXTREMES
The alarm was operated a t temperatures varying from 0" to 100" F. over a range of relative humidities from 10 t o 90%. In these tests two difficulties arose. The first was a t 100" F. and 10% relative humidity, when the wetted tape dried out before the end of the 5-minute cycle. Several compounds known to retain moisture were employed both on the paper and in the chemical solution, but no successful results were obtained. Table I11 lists the compounds tested and the reasons they were not satisfactory. By shortening the cycle time t o 3 minutes the same
sensitivity to agent was achieved, on a dosage basis, as under ordinary conditions. However, the minimum detectable concentration was raised to 0.04 p.p.m. of GB. The other difficulty occurred a t high temperature and high relative humidity (100O F. and above 80% relative humidity). Under these conditions in a test chamber, moisture condenses on the unit and causes electrical leakage in the circuit, which creates a drift in the null point of the alarm and a serious decrease in sensitivity. If the unit is renulled after this, adequate operation is still obtained. Proper potting of the photocells and high impedance circuit will probably eliminate this difficulty. However, it has not been serious under actual operating conditions encountered in hlaryland. When the operating temperature drops below freezing, an antifreeze may be added to the aqueous solution to prevent a freeze-up. The antifreeze used is isopropyl alcohol. Table IV shows a number of different antifreezes that were tested and the results of these tests. If it is not desirable to use an antifreeze a t temperatures below freezing, an electrical heater is provided for alarm operation. ROUGH HANDLING TESTS
The instrument is extremely rugged and was subjected to rough handling tests similar to those given the AN/ PRC-7, commonly known as the Walkie Talkie radio. The alarm successfully passed these t)ests, shock. vibration, immersion, drop test, etc. At the request of Army Field Forces, a unit was air-dropped by parachute from a plane. The alarm was started up immediately after the drop and operated satisfac-
Table 111.
Compounds Used to Retain Moisture
Compound Glycerol Ethylene glycol Sorbitol Methyl Cellosolve Lithium chloride Lithium bromide Calcium chloride Colloidal silica gel
Cause for Rejection Colored soln. Colored soln. Ineffective Colored soln. Ineffective Ineffective Ineffective Ineffective
Table IV. Antifreeze Additives Remarks Additive Poor Ct, rapid drying, Methanol poor stability Fair stability, fairly Ethyl alcohol good sensitivity Poor stability, slush 1-Propanol point of 12" F. Satisfactory storage sta2-Propanol bility, blank time, and sensitivity Solubility in waterrtoo 1-Butanol low Solubility in water too 2-Butanol
+
10F
Very rapid color formation, high viscosity Poor stability, high viscosity Poor stability Low water solubility, rapid color formation Low water solubility, rapid color formation
Ethylene glycol Glycerol Acetone Methyl ethyl ketone Tetrahydrofuran
use in the field. It is lightweight and requires little electrical power for operation so that a portable power supply may be used with the unit. The instrument will operate unattended for 12hour periods and responds to extremely low dosages of G-agent. It is reasonably free from chemical interference in the field and rugged enough to withstand rough handling by combat troops. The alarm must be serviced every 12 hours with solution and paper tape, and the air knockout pot and platen must be cleaned. Other maintenance and lubrication duties are required every 1000 hours of operation. ACKNOWLEDGMENT
The authors wish to express their appreciation of the technical guidance given by Robert Picard, formerly of Radio Corp. of America, and Solomon Love, Army Chemical Corps. In addition, they are pleased to acknowledge the efforts of many colleagues in this work, particularly Saul Zelkind, Andrew Davis, Robert Gamson, for chemical assistance and Ronald Ruefenacht, Robert Jones, William Russell, Edward C. Luke, and William Keane for their engineering assistance. LITERATURE CITED
torily. The unit is completely waterproof when the caps and covers are closed. In operation, the alarm operated satisfactory when placed in a trailer attached to an Army truck and driven Over 250 miles of rough fields and roads. CONCLUSIONS
The alarm is satisfactory for portable
(1) Gehauf, B., Epstein, J., Wilson, G. B.,
Witten, B., Sass, S., Bauer, V. E., Rueggeberg, W. H. C., ANAL. CHEII.29, 278 (1957). (2) Gehauf, B., Goldenson, J., Zbid., 29,276 (1957). for revien- xfarch 23, 12157. Accepted January 8, 1958. Division of
Analytical Chemistry, 130th Meeting, ACS, Atlantic City, N. J., September 1956.
Alarms and Analyzers for Nerve Gas Vapors R. H. CHERRY, G. M. FOLEY, C. 0.BADGETT,' and R. D. EANES leeds & Northrup Co., Philadelphia, Pa.
H. R. SMITH Chemical Warfare laboratory, Army Chemical Center, Md. ,Nerve gases give no sensory warning when lethal concentrations are present. Automatic nerve gas alarms use the Schoenemann reaction with indole reacting with the nerve gas to form a fluorescent compound, indoxyl. An automatic chemical processing system is combined with a fluorescence photometer to operate as a continuous alarm or analyzer. Data are presented to
select the reagents giving maximum sensitivity in a given photometer. Studies on reagent solutions led to the selection of two separate solutions, and to the use of acid-stabilized hydrogen peroxide and carbonate-bicarbonate buffering. The instruments will give warning before any injury occurs, and may b e used as calibrated analyzers.
S
of nerve gases (Gagents) during manufacture, storage, and laboratory use requires sensitive detection equipment, capable of giving an alarm before personnel are exposed t o harmful dosages. The instruments and chemical systems deAFE HANDLING
l Present address, Tele-Tronics Co., Ambler, Pa.
VOL. 30, NO. 7, JULY 1958
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