INSTRUMENTATION A supersensitive gas detector permits accurate detection o f toxic or combustible gases in e x t r e m e l y l o w concentrations / " I N SEVERAL occasions, we h a v e h a d ^-'^ t h e o p p o r t u n i t y of describing equip m e n t manufactured b y Taller & Cooper, Inc. Of the m a n y products, these h a v e included d a t a printers, conversion units a n d d a t a assimilation, recording, and tallying devices. T h e c o m p a n y is now producing several chemical analyzers, detectors, and recorders, one of which we describe here. I t is of interest a n d importance, n o t only because it is ex tremely sensitive, b u t t h e chemistry, upon which it is based, is ingenious a n d presents m a n y additional possibilities which h a v e n o t been investigated as yet. Supersensitive
Gas
Detector
T h r o u g h t h e courtesy and assistance of M . D . Weiss, chief of the Chemical Division of Taller & Cooper, Inc., 75 F r o n t St., Brooklyn 1, Ν . Υ., we are able to present details of t h e supersensi tive gas detector which permits t h e accurate detection of toxic or combus tible gases in extremely low concentra tions. T h e i n s t r u m e n t is based u p o n the liberation of mercury vapor as a con sequence of reacting activated mercuric oxide with the gas in question a t a suit able temperature, and then measuring t h e mercury vapor photoelectrically b y t h e absorption of its own resonance line 2537 A. T h e fundamental chemistry of this class of reaction was worked out in 1947 [McCullough, J. D., Crane, R. Α., a n d Beckman,
A.
O.,
ANAL.
CHEM.,
19,
999 (1947) ]. This s t u d y was limited t o t h e determination of carbon monoxide
Figure 1. VOLUME
in air b y the use of red mercuric oxide a n d m a d e use of t h e reaction : CO (gas) + H g O (solid, red) —> H g (gas) + C 0 2 (gas) I t can be shown t h a t this reaction is favorable thermodynamically because the free energy change is negative a n d of t h e order of 58 kcal. as written above. T h e gaseous sample was passed through a reaction t u b e containing granular red mercuric oxide held a t a t e m p e r a t u r e of 175° t o 200° C. I t was shown t h a t t h e loss in weight of t h e reaction t u b e dur ing t h e passage of t h e sample is a n exact measure of the q u a n t i t y of carbon monoxide present and involves a highly advantageous gravimetric factor. I t was indicated a t t h a t time t h a t this re search established the feasibility of the method and its suitability for deter mining the liberated mercury b y a n in strumental method, of which t h e pres ent Taller & Cooper instrument is a n example. Ordinary red mercuric oxide is too finely divided for this m e t h o d a n d a means of preparing granular reagent b y t h e rapid, b u t controlled, ignition of mercuric nitrate was described. I t has been known for m a n y years t h a t mercury vapor can be determined b y measuring t h e absorption of t h e first resonance line of t h e mercury spectrum, λ = 2537 A. T h e absorption coeffi cient is enormous; indeed, in all high pressure mercury arcs, this line is com pletely reversed b y absorption within the arc t u b e . Special low pressure arcs or mercury lamps avoid this condition
S c h e m a t i c Diagram of Gas Detector
2 6 , N O . 9, S E P T E M B E R
1954
by Ralph H. Müller
a n d in some of them, this resonance line constitutes a large proportion of t h e t o t a l emitted radiation. T h e process of absorption is extremely complex, being a m a t t e r of successive absorption a n d re-emission and, in a sense, is, therefore, a m a t t e r of multiple scattering. I n effect, it becomes a n extremely sensitive means of detecting mercury vapor.
Figure 2.
Complete Unit
T h e Taller & Cooper i n s t r u m e n t works as indicated in Figure 1. B o t h process stream and a known reference sample are drawn through filters a n d t h e n t h r o u g h identical heated reaction chambers. T h e mercury vapor liberated in each line passes through q u a r t z absorption cells in which the absorption of the ultraviolet line is measured b y phototubes. A common source illuminates b o t h photometric systems. A complete unit embodying these elements is shown in Figure 2, a n d a n interior view in Figure 3. Figure 4 shows Model M . P . , which combines t h e detachable mercury vapor detector (upper unit) b u t includes filters, heating units, a n d balance indication. Typical specifications of the Model L.P. or laboratory model a r e : sensitivity, 5 p a r t s per 39 A
INSTRUMENTATION
billion; accuracy, 0.5% of full scale; ranges, 0-10, 0-100, 0-200 p.p.m.; height, 24 inches; width, 15 inches; depth, 9 inches; weight, 75 pounds; power, 150 watts, 115 volts, 60-cycle single phase.
Figure 3. Interior View
REQUIRES NO
LUBRICANT
F&P UI trama χ SEPARATORY FUNNEL Now — from the laboratories of Fischer & Porter, comes the new F&P-developed Class Separatory Funnel. With the new stopcock, lubrication and freezing problems are ended. Gone are costly leakages and blowouts dur ing centrifuging. Product contamination is completely avoided. Note the unconventional design of the F&P Separatory Funnel. The Ultramax* valve consists of a plug of Teflonf turning on a natural glazed surface of unground, pre cisely-formed Pyrex$ tubing. Complete int e r c h a n g e a b i l i t y of p a r t s , all c o r r o s i o n resistant, makes replacement easy. Funnel sizes available range from 30 ml to 2 liters, and come in the globe, squibb or cylindrical type. Smaller sizes — 30 ml to 125 ml — are especially adaptable for cen trifuging. Cylindrical type, 30 ml, is perfect for vitamin analysis. Complete details are yours for the asking. Or test the new F&P Separatory Funnel in your own laboratory for 30 days without cost. Write today!
FP
PLUG OF TEFLON will not freeze or leak. Natural glazed finish of barrel is less susceptible to alkali attack. No lubricant r e q u i r e d stopcock is not affected by either organic or water phase. Completely interchange able parts — all corrosion-resistant. *pat. pending t t . m . for Du Pont tetrafluoroethylene resin Jt.m. Corning Glass LA1(U5
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FISCHER & PORTER CO. 1594 County Line Road, Hatbaro, Penna.
Company owned sales and service branches strategically located throughout the world. Far further information, circle number 40 A on Readers' Service Card, page 45 A
40A
Other models include the A.P. or continuous model, the range of which is 0 to 200 p.p.m. It has automatic zeroing, automatic heat control, and strip chart recorder for continuous record. Other special models are built to customer's requirements. The fol lowing substances have been determined successfully by this instrument: carbon monoxide, hydrogen, ethylene, acety lene, formaldehyde, hydrogen sulfide, acrolein, saturated hydrocarbons, lower aldehydes, methane, ethane, and pro pane. Water vapor and oxygen in inert gases have been measured by their effect in causing a reduction in mercury vapor concentration.
Figure 4.
Model M.P. Detector
The same instrument can be used in a slightly different manner (not involving the mercury vapor), by measuring the ultraviolet absorption of such substances as benzene, toluene, ethanol, methanol, gasoline, aromatic hydrocarbons, al cohols, and water vapor. ANALYTICAL
CHEMISTRY
TEMPERATURE CONTROLS &%e£ewted i*t *764U4cut*U
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tie TOonùC Octet f THERMOREGULATORS
For extremely close t e m p e r a t u r e c o n t r o l , A m i n c o offers t i m e tested, reliable thermoregulators for use In water, o i l , or a i r . Thousands now in successful use. Convenient t o m o u n t . Pro tecting tubes available. Quickset b i m e t a l adjustable t y p e f o r t e m p e r a t u r e ranges as low as m i n u s 73° t o plus 177° C , a n d as high as 260° t o 538° C. M e t a s t a t i c mercury (glass) t y p e a d j u s t able for temperatures f r o m m i n u s 30° t o plus 250° C.
RELAYS
THERMOREGULATORS
Electronic relay ( i l l u s t r a t e d ) has a power amplification of 200,000,000 and provides an ultrasensitive, reliable means for controlling a power circuit f r o m a l o w - c u r r e n t or high-resist ance circuit. Supersensitive type (power a m p l i f i c a t i o n , 50,000) is designed particularly for a c t u a t i o n by thermoregulators a n d other delicate c o n t a c t - m a k i n g devices. All are available for operation on 117, 208, or 230 volts, 60 cycles. N o r m a l l y open or n o r m a l l y closed single-pole operation obtained by a flip of a switch.
STIRRERS Q u i e t , powerful, efficient units for use in constant t e m p e r a t u r e baths. A variety of types are available for every laboratory need : (1) universal variable-speed t y p e : slow speed, 100 t o 500 r p m . ; high speed, 1000 t o 5000 r p m . ; 1/80 h p . ; 115 volts a-c. or d - e . (2) heavy-duty i n d u c t i o n t y p e : 1550 r p m . ; 1/30 h p . ; 115 volts a-c. (3) m i d g e t induction t y p e : 1550 r p m . ; 1/150 h p . ; 115 volts a-c. ( 4 ) m i d g e t variable-speed t y p e : 500 t o 5000 r p m . ; 1/100 h p . ; 115 volts a-e.
IMMERSION HEATERS
PUMPS
Ideal for precise constant t e m p e r a t u r e applications w h e r e i n s t a n t response t o t h e r m o s t a t i c action is desirable. Patented LoLag construction, w i t h sheaths of copper, steel, or stainless steel, for 115 or 230 volts. Flexible type can be bent t o a n y shape t o fit inside a n y vessel. Wattages f r o m 125 t o 2000. Pipef i t t i n g t y p e for screwing into walls of vessels are available f o r wattages f r o m 600 t o 2500.
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