SOUITIOHS FOR T1TBATJOM PROBLEMS 0ΟΟΘΟ
At Corco, we make 132 standard solu tions — and uncounted special or custom solutions. Volumetric. Per centage. For Aqueous and non aqueous titrations. Special solutions to meet ACS and ASTM requirements. Indicators. Buffers. Clinical reagents. All within an accuracy to 0.05%. As many companies come to Corco for normal solutions as those for special normalities. We make them just as easily and just as well. Because Corco makes only reagent-grade solutions. (Reagent acids, bases, and specialty chemi cals, too.) Corco has the solutions — spe cial or standard — in pints, gallons, five-gallons and drums. Write or call for your copy of our booklet with that title. Or circle the number.
CORCO CHEMICAL CORPORATION Manufacturers of Reagent & Electronic Chemicals Tyburn Road & Cedar Lane · Fairless Hills, Pa. 19030
(215) 295-5006
omizer, spray chamber, burner, and control unit, and sold in 1948 for $750. Paul Gilbert continued to improve this accessory and by 1951 had per fected an atomizer burner t h a t gave superior performance plus reduced size and lowered costs ($395) (10). This burner has been supplied with many instruments, Beckman and nonBeckman, and is still produced. When the DU was first developed, it required dry cells as well as a leadacid storage battery, at t h a t time a normal, acceptable requirement. Al though the storage battery functioned well in the automobile and was inex pensive, it proved troublesome under intermittent use in the laboratory. T h e trickle charger introduced in 1951 helped, but users and dealers began developing their own AC power supplies to eliminate the storage bat tery. Beckman made several a t t e m p t s to develop an acceptable power supply, but for Beckman the problem was far more complex. T h e challenge lay in developing a replacement for all the batteries and simultaneously accom modating all the existing DU's in the field. This necessitated development in one package of 10 separate, electri cally isolated supplies covering a range from 2 to 600 V with regulation better than 0.02%. A paper by Greenough et al. (11) was ultimately recognized as offering a method of accomplishing this goal. Greenough's principle of operation required the conversion of a regulated high-voltage DC source to AC with a multivibrator. T h e regulated highvoltage AC signal was then converted to the required voltages with a trans former followed by rectification to DC. By the use of multiple transform er secondaries, the separate electrical ly isolated power sources could be ob tained. T o economize the rectification step, the multivibrator frequency was initially set at 2 kHz. Four prototypes were built and passed the required specifications, but the supply emitted an objectionable whistle. T h e frequen cy was then raised above the audible range (ultimately to 20 kHz). Because of the insistent demand for AC operation, a fateful decision was made to make 250 units without fol lowing the normal procedure of first field testing a few instruments. Unfor tunately, because of subtle variations in distributed capacitance, no two in struments behaved exactly alike. Worse, the supplies began to fail in the field because of excessive internal heat. Although the power supplies failed within their warranty period, they lasted long enough to prove the princi ple of operation. Few users wanted to return to battery operation, b u t fail
CIRCLE 32 ON READER SERVICE CARD 284 A ·
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ure of the power supply units de pressed sales of both the power supplies and the basic spectrophotom eter. Eventually, of course, the prob lems were solved. Most of the DU's sold after 1958 were AC operated, and an effective quality control program prevented repetition of the power sup ply problem. T h e DU was only the first of a long line of spectrophotometers. Within a year after the first DU was delivered, work started on infrared spectropho tometers. Model D U - 2 , Successor. Scientific instruments are sensitive to style as well as function. Throughout its mar keting history, Beckman Instruments has successfully and continuously upgraded its instruments and has in troduced new models regularly. De spite this fact, the DU remained out wardly unchanged for 23 years. Other ultraviolet spectrophotometers had been introduced, but the demand for the high-precision, nonscanning ultra violet spectrophotometer persisted. T h e DU's successor would have to be able to perform the thousands of ana lytical procedures developed for the DU with a minimum of operator re training. Over the years, four major a t t e m p t s were made. T h e DU-2, introduced in 1964, was relatively little changed from the orig inal DU. T h e major revisions were in the styling and location of components for ease of manipulation (12). It ac cepted most of the earlier designed ac cessories, including the AC power sup ply· Accessories continued to be devel oped for the DU-2 as listed in Table I. T h e new accessories automated fixed wavelength absorption analysis. However, by 1972 the price of a digi tal, direct-reading DU-2 with AC power supply had risen to $7 885, which was not competitive with other integrated-circuit spectrophotome ters. When the DU-2 was discontinued in mid-1976, only the accessories de veloped before 1959 were still in pro duction. In all, over 30 000 DU and DU-2 instruments have been pro duced. Few scientific instruments have matched the 35-year commercial life enjoyed by the DU and DU-2, nor have many been so widely copied. Exact and near exact copies of the DU have been commercially produced in J a p a n , England, and Russia. T h e DU has also been supplied as a component in the spectrophotometers manufac tured by Process and Instrument Co., Warren Electronics, Inc. (subsequent ly incorporated within Perkin-Elmer Co.), and the Gilford Instruments Labs, Inc. Model D U R , Process. T h e first at t e m p t a t automating the DU was for
