PRECISION-FREAS
INSTRUMENTATION pilot light, and meter. The units are readily removed from the instrument; interunit cabling is done with shielded rubber-covered cables fitted with AN connectors. These units comprise an ionization gage which measures pressure and also automatically cuts power to the mass' spectrometer when the pressure rises above 0.1 micron. A circuit is also included for outgassing the ion gage grid. A second unit supplies the spectrometer filament and regulates the electron beam which ionizes the gas sample. A third unit furnishes the high potentials for accelerating ions of different mass. A fourth supplies the magnet current which can be set to several magnetic field strengths with a tap switch. Another unit contains a preamplifier consisting of an electrometer tube and high input resistor, both enclosed in an evacuated iron can. The main amplifier is a carefully shielded feedback circuit with regulated power supply. The pumping system utilizes a two-stage mercury diffusion pump and Welch Duoseal forepump which are connected to the spectrometer tube through a large-bore trap immersed in a Dewar flask. The diffusion pump heater is monitored by a protective thermostat to guard against failure of the cooling water supply. The glass sample manifold is mounted on a removable panel and a second Welch Duoseal pump is used for its evacuation and permits a mercury Toepler pump to transfer the gas from the sampling bulb through a capillary leak into the spectrometer tube. Dispersion Staining Bausch & Lomb Optical Co. reports (Dec·. 31) the development of "dispersion staining" by G. C. Crossmon—a new technique adaptable to standard microscopic equipment whereby the various components of a colorless sample can be made to appear in various colors. It is achieved by passing white light from the microscope lamp through a darkfield substage lens and striking the sample at a high angle. With the sample placed in .the correct immersion liquid, only certain wave lengths will enter the microscope and these will vary with the nature of the optically inhomogeneous components of the sample. According to Crossmon, the use of dyes to stain tissues or bacteria is not likely to be supplanted, especially in those cases where absorption of the dye is a specific chemical characteristic of the material. In all other respects, the technique promises to extend the use of the microscope very considerably in the examination of foods, drugs, ores, minerals, tissues, and textile fibers. Automatic Spectrophotometer Our report on the Instrument Society of America Conference [ANAL. CHEM., 19, 817 (1947)] mentioned a paper by R. H. Kienle and E. I. Stearns on the "Adaptation of the Automatic Spectrophotometer for Special Measurements." This paper has been published in full [Instruments, 20, 1057 (1947)]. Twenty-three modifications of this instrument are described for performing a wide range of optical measurements. This article is particularly valuable inasmuch as most of the information has been available only in letters patent. Convectron Tube The Convectron tube which we described in the December column is manufactured by the Eclipse-Pioneer Division; Bendix Aviation Corp., Teterboro, N. J.
The " s t a n d a r d o f excellence" I n fine constant t e m p e r a t u r e equipment.
Year Guarantee. [ The manufacturer's certificate goes w i t h ; every Freas oven. It guarantees the oven against defects in materials and workmanship for five years.
• Five-Year Guarantee, for heating unit and thermostat • Hydraulic Thermostat, sensitive to % ° C . • Finger-Tip Temperature Control • Nickel-Chromium Heater Bank • Ail-Metal Welded Cabinets • Glass Wool Insulation, 3 " thick, in doors and walls • Stainless Steel Interiors, Rustproof Iron Exteriors
Mechanical Convection models, for greatest efficiency: Forced a i r circulation provides u n i f o r m heat t h r o u g h o u t the oven, quickly a n d surely. Heat transfer is accelerated, d r y i n g time is r e d u c e d , oven l o a d i n g capacity is increased. Air velocity adjustable between 7 5 a n d 250 feet per minute.
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Gravity Convection models, for general use: Designed t o t a k e every a d v a n t a g e of temperature differentials t o speed heat t r a n s f e r ; I d e a l f o r a l l applications not r e q u i r i n g t h e advantages of mechanical convection, or where space is a t a premium. Precision—Freas Ovens are available in a variety of sizes and in t w o temperature ranges. They are furnished w i t h adjustable shelves, 0-300° C. thermometer. Neon pilot lamp, and for 115 or 230 volts, 4.C. or D.C. current. One popular size has a heating chamber 1 3 " w i d e , 14" deep, and 13" high, and is priced as follows:
