INSTRUMENTATION
Meet the PCQ®-X7
A versatile new photo chemical lamp at an easy-does-it price
The PCQ-X1 is packed w i t h want-most features. It's a cool burning, low-pressure, short-wave lamp of h i g h u l t r a v i o l e t i n t e n s i t y . W i t h t h e PCQ-X1 you can perform a wide variety of photo chemical operations w i t h o u t need for special accessories. The unit, w i t h its cylindrical ALZAC reflector in place, produces an intensity of 30,000/iW/cm 2 of 2537 A radiation. Eighty to 90 percent of the PCQ-X1 's irradiance is at this extremely efficient 2537 A figure. The lamp is a compact 6V4" χ 8 3 Α" χ 5VA". Plugs into any 120-VAC outlet; operates at a relatively cool 45°C. You can turn off the tubes separately (to vary radiation) or all at once. The price of this precision laboratory instrument is only $89.50 list (less stand). Write for descriptive literature, or see your laboratory equipment dealer.
BLAK-RAY U L T R A V I O L E T METER is a
hand-sized photoelectric device that allows duplication of measurements with the PCQ-X1 and other ultraviolet and photochemical apparatus. It gives you a precision means of establishing and repeating dosage of radiation. Models are available for either short wave or long-wave ultraviolet.
ULTRA-VIOLET S u i t e 117 — 5114 W a l n u t
PRODUCTS,
Grove
Specialists
Ave.,
San
in specialty lamps since 1932
Circle No. 75 on Readers' Service Card
116 A • ANALYTICAL CHEMISTRY
INC.
Gabriel, California
91778
For a given value of constant b, which defines Ee, an infinite number of hyperbolas can be drawn, all converg ing to Ee at t — » , depending upon the choice of constant a. These would range from almost instantaneous re sponse to almost infinitely slow or sluggish response. The ratio of these constants α (intercept) and 6 (slope) is a useful quantity; for example, the half-time, ti/, — alb. The time re quired to attain any desired fraction / of the equilibrium value Ee is simply: t, = [//(l - /)] X a/b. Beyond this, constant α is a reliable response speed measure of the electrode, but more use ful when used in the ratio alb. Some doubt may be expressed that Ee is attained only at infinite time. The apparent stabilization at finite and relatively short times is a function of the sensitivity of the detecting system, and simple "eyeballing" of a recorder trace is not reliable. At very long time intervals after apparent equilibrium had been attained, we could detect in crements in potential of the order of 10-50 μ,ν. We have examined several curves reported in the literature, as far as our patience in disinterring the data permitted, and they were found to yield well to this treatment. The empirical approach to this prob lem is useful because the calculated values agree with the observations with the same precision that the data are known. For want of better informa tion, such results are preferable to plausible theoretical derivations yield ing results in which the agreement be tween calculated and observed is called "encouraging." The hyperbolic relationship is not without significance for an ultimate un derstanding of the time-response phe nomenon. It bears a formal, if not ac cidental, similarity to the Langmuir ad sorption isotherm and is, at least circuitwise, akin to the equivalent re sistance of two resistors in parallel, one of which is changing uniformly with time. In the latter case, it is conceiv able that such an arrangement could be set up as a compensator to turn out an emf value corresponding to the true E0 value over a reasonable period of elapsed time. One might even drive it with an alarm clock. Data supporting these conclusions are being submitted to this Journal. We obtrude these few generalizations upon this commentary merely in the sense that there are other questions re lating to selective ion electrodes worthy of detailed inquiry. They should not detract from the larger design and vista which Dr. Rechnitz has outlined for us.
