Instrumentation usually made with hot tungsten fila ment lamps which give continua over this range. Filament lamps are rugged, low-cost units sufficiently bright for nearly all work. Special broad-band-type tung sten lamps are frequently used as stan dard sources. These can be calibrated and verified by the National Bureau of Standards. The shape of the radiating band on these lamps allows optimum imaging at the slit and thus uniform illumination. Spectral characteristics of the tungsten lamp are basically those of a blackbody. Therefore, measure ments very far from the peak wave length are susceptible to stray light ef fects. In the region above 2 p,m, blackbodytype sources without envelopes are commonly used. The same spectral characteristics cited for the tungsten lamp apply to these as well. The un even spectral distribution is particularly serious for long-wavelength measure ments. A popular source of this type em ploys nichromc wire coils. These are simple and rugged, but less intense than other infrared sources. A black oxide forms on the wire which gives accept able emissivity. Temperattires up to J 1 0 0 ° C can be reached.
THE COMPLETE POTENTIOSTAT! The new PAR™ Potentiostat/Galvanostat provides more features, modes of operation and flexibility than ever before available.
Plug-in m o d u l e s provide m a x i m u m flexibility in r e a d o u t . Positive feed b a c k IR c o m p e n s a t i o n , high current m e a s u r e m e n t a n d g a l v a n o s t a t i c capabilities up to 1 A are available. The Model 173 replaces a p o t e n tiostat, t w o voilage s o u r c e s a n d a c u r r e n t - m e a s u r i n g device. Price of the Model 173 is $2200 including probe. Digital version, $2560. C u r r e n t r e a d o u t module, $145. I-E converter, $550. 100 mA output ver sion less t h a n $2000. For m o r e data, contact P r n c e t o n Applied R e s e a r c h Corp., Box 565, Princeton, N.J. 08540; t e l e p h o n e (609) 452-2111. \PRINCETON APPLIED RESEARCH CORPORATION
In one con
figuration, the hot coil is used to heat a ceramic sleeve which modifies the spec tral output. A still hotter, and therefore brighter, source is the Nernst glower which has ati operating temperature as high as 1500°C. This source is generally pre ferred if longer wavelength work is in volved—e.g., to about 50 ^m. Nernst glowers are constructed from yttriasfabilized zireonia in the form of nar row rods. Electrical connections are made with coated platinum wires. Although more intense than wire fil ament sotirces, Nernst glowers have several disadvantages. The rod has a negative coefficient of resistance and must be preheated to be conductive. Therefore, auxiliary heaters must be provided as well as a ballast system to prevent overheating. Nernst glowers are fragile, particularly at the points of electrical connection. During use, platinum diffuses into the ceramic ma terial particularly when local overheat ing or arcing occurs. This weakens the glower joints and eventually causes fail ure. Coating the joints with ceramic cement reduces the evaporation of platinum and increases life to some ex tent. Until recently, another disadvantage of Nernst glowers has been their limita tion to diameters of one mm or less. In the far infrared, where large slit widths are required to increase energy
• Remote electrometer probe (mounted in signal cable) • lOnS2 input impedance • Slewing rate: 10V/Vs
• ± 100 V compliance, 1 A max. • T w o independent, internal potential sources • High speed electronic potential switching
112
CIRCLE 144 ON READER SERVICE CARD
AVAILABLE IN 15, 20, 100 and 220 MICROLITER SIZES
THE NEW GLASS BARREL Drummond
MICROTROL
®
The Druminond Microtrol is α simple, l o w cost microliter delivery system. It combines the precise delivery capability of an expensive syringe w i t h all the advantages of a disposable micropipette.
1. A clean syringe bore for each sample. 2. A disposable stainless steel plunger for each sample on the 15 and 20 microliter units. 3.
A teflon tipped stainless steel plunger is used with the 100 and 220 microliter units.
4.
Overall accuracy of one percent.
5. Dependability backed by Drummond, the originator and leader in disposable mîcropipettes and precision glass tubing.
15 μ\
20 μΙ
100 β\
220 μ\
MICROTROL w i t h 100 $14,00 MICROTROL w i t h 100 REPLACEMENT BORES
SI 2.00 .
. $12.00
100 REPLACEMENT BORES . .
. . $ 5.50 . . .
$ 5.50 . . . . . .
$ 6.25 .
. $ 6.25
REPLACEMENT PLUNGERS
. . $ 2.00 (per C)
$ 2.00
$ 1.00 (each)
$ 1.00
. . $ 1.00 . .
$ 1.00 . . . . . .
$ 1.00 .
$ 1.00
REPLACEMENT
HANDLES
..
..
Made
i n U.S.A. by
Drummond Scientific Company SOO
PARKWAY
·
BROOMALL
·
PENNSYLVANIA
«
1900B
CIRCLE 45 ON READER SERVICE CARD
ANALYTICAL CHEMISTRY, VOL. 43, NO. 6, MAY 1971 • 83 A
