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BETHLEHEM PLURO STOPPER
for Laboratories
ONE PLURO STOPPER EQUALS U
and Glass Shops
STANDARD STOPPERS
Provide vacuum tight fit for all size openings — 18 mm to 100 mm. An ideal bushing be^ tween tubing, bottles and other glassware. FOR GLASSBLOWING. One stopper will fit every size tubing ranging from 18 mm to 100 mm. Can be used for plug or air vent with swivel and blowhose. STANDARD—Range 18 to 100 mm RS2A Rubber $3.95 ea. RS2B Neoprene 4.55 " JUNIOR—Range 18 to 70 mm RS2C Rubber $2.00 ea. RS2D Neoprene 2.30 "
BETHLEHEM Apparatus Company, Inc. HELLERTOWN, PENNSYLVANIA
For further information, circle number 22 A-1 on Readers' Service Card, page 89 A
NOW . . . an automatic, recording CHROMATOGRAPHIC REFRACTOMETER that cuts research work
up to 7 5 % No longer is it necessary for you to perform all the time-consuming work associated with chromatographic analysis. This differential refractometer does all the work — reliably — accurately. Simply start the test, and the analysis is made automatically — unattended. The final product . . . an accurate, permanent recording of the results . . . a record you can examine immediately or file for future use. Operation is so simple that even your most inexperienced personnel can perform critical analyses with ease. What's more, where great differentials are encountered the exclusive Phoenix range-extension system permits setting the indicator on scale without the annoyance of changing cells . . . without upsetting the zero calibration . . . and without loss of sensitivity or accuracy. A single dial adjustment is all that's required. SEND FOR BULLETIN R-1000. No obligation. For your convenience, just attach this ad to your letterhead — or write:
PPI
PHOENIX
PRECISION
INSTRUMENT CO.
3805 N. 5th STREET, PHILADELPHIA 40. PA.
For further information, circle number 22 A-2 on Readers' Service Card, page 89 A
22 A
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ANALYTICAL CHEMISTRY
chemical identity of the sample. Thus, a glass electrode converts hydrogen ion activity into a voltage proportional to it; a bolometer converts thermal energy (as in an infrared beam that has passed through a specimen) into a proportional resistance change; a Geiger-Muller tube converts an x-ray beam (such as the fluorescent radiation from a sample in an x-ray spectrometer) into a series of current pulses. The amplifier raises the signal from the transducer to a usable level. Sometimes the transducer is its own amplifier; which is equivalent to saying that the primary signal is strong enough to be used to operate the output device without a special amplification circuit. More often, however, some amplification is used. For example, in an infrared spectrophotometer, the energy striking the detector may be of the order of magnitude of 10~s watt, and the power necessary to operate the output device is of the order of watts, so that a power amplification by a factor of 108 is necessary. On the other hand, in a flame photometer that employs barrier-layer type photocells the transducer output directly operates the output device (in this case, a sensitive galvanometer). In a pen-andink recording polarograph, the transducer output must be amplified by a factor of about 103. The computer section of an instrument is necessary to change the primary signal into a form suitable for operation of the output stage in order to provide the desired type of information. This may involve changing the signal from a current into a voltage, or converting from d.c. to a.c, or vice versa, or changing the wave form of a signal from sinusoidal to square, or changing the frequency, etc. More significantly, the function of the computer section may be to compare the transducer or amplifier output with a standard signal, so that the final output of the instrument will be proportional to the ratio (or, if preferred, difference) of these two. Sometimes a computer section is employed to square, form a reciprocal or logarithm, differentiate, or integrate the primary signal, in order to present an output that is more useful than the raw data would be. The output of the instrument is the device utilized to present the signal in a form useful to the operator. Often the output device is simply a meter, the pointer deflection of which is read. Where warranted, the meter may be replaced by a pen-and-ink recorder, which gives a record of the deflection on a chart, and is uniquely valuable for obtaining information as a func-
