26 A A N A L Y T I C A L C H E M I S T R Y

In Stock, for Immediate Shipment

VARI-SPEED STIRRERS

The only labora­tory stirrer com­bining positive gear drive with built-in electric g o v e r n o r , in­stead of a rheo­stat, for speed control without loss of power at low speeds.

• Increased Torque at Low Speeds · Electric Governor for Speed Control · Built-in Reduction Gears, No Slippage · Speed Unaffected by Voltage Fluctuations · Powerful, Con­tinuous-Duty Motor Rated 1/15 H. P., Underwriters' Approved · Sturdy Motor With Plus Features · Utmost Mounting Flexibility

No. M-38353 (above). "Vari-Speed" Stirrer. O n metal base with 5J-£" dia. rubber disc to prevent sliding; of glassware. Rubber feet prevent marring of table tops. Stirrer height adjustable to place chuck 5J^" to 10J^ff from base . Dis­tance between mounting rod and stirrer rod 4". Includes )-2 χ Q^/i" mounting rod, %" chuck, glass stirring rod 6" long, cord and plug. For 115 Volts. A. C. or D. C $40.50

lia ^ ,^Ζ»ΛΪΛ Mo. M-38351 (left) "Vari-Speed" Stirrer. O n semi-circular cast iron support stand, with J^w χ 24" nickel "plated rod and 90° support clamp. Radius of base 63^". Includes y^n χ 6%" mounting rod, 3^" chuck, glass stirring rod 6" long, cord and plug. For 115 Volts. A. C. or D. C $40.50

No. M-383S6 (right) "Vari-Speed" Stirrer, less base. With mounting rod ^£ff χ 6%w ; Mff chuck; glass stirring rod 6" long, and 6 ft. rubber covered cord with plug. For 115 Volts. A. C. D. C . $34.50

ARTHUR S. & COMPANY

109 W. Hubbard St. Chicago 10, Illinois

I N S T R U M E N T A T I O N

Figure 2

when no bolometer current is passing. Provision is made for evacuating the bolometer case by means of a mechanical oil pump to a pressure between 0.01 and 0.1 mm. of mercury. The sensi­tivity is improved and "gas microphonics" or "swish" is greatly reduced. Figure 3 illustrates the bolometer assembly.

The recording drum rotates synchronously with the rotation of the wave-length mirror. The amplified bolometer signal drives a comb-shaped diaphragm near the Globar source in such a way that it trims the reference beam until it is equal to the sample beam. The motion of the comb is coupled to the pen drive which records the transmission of the sample cell.

Figure 3. High-Speed Bolometer

Two amplifiers are provided. The first, a voltage amplifier, is a four-stage resistance coupled circuit tuned to 10 c.p.s. I t has a gain of about 5 X 107 and an inherent noise level of 5 X 1 0 - 9

volt, the same order of magnitude as the bolometer noise. At one half of maximum gain the band pass is about 5 c.p.s. A three-stage direct current power amplifier furnishes power for the 60 c.p.s. output of the voltage amplifier after rectification by the commutator of the light beam interrupter. This amplifier has an effective gain of approximately 50 and a noise level of less than 0.3 volt.

The entire instrument measures 43 inches X 43 inches X 51 inches and weighs 300 pounds. The only utilities required are a source of 110-volt alternating current 60-cycle, single-phase and a water supply through 0.25-inch PT.

A typical record taken with this instrument is shown in Figure 4. The chart is 5 by 17.5 inches and shows the absorption of NH) at 100-mm. pressure in a cell 10 cm. long, recorded from 2 to 16 microns.

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