A MODIFIED BECKMAN 

 MODEL DU SPECTROPHOTOMETER 

 FOR SEAGOING USE 



by 

 Robert W. Holmes and Robert J. Linn 



ABSTRACT 



Several modifications of the Beckman DU Spectrophotometer are 

 described which facilitate operation and maintenance on a seagoing 

 vessel. These include the replacement of the desiccant holders in the 

 instrument with readily accessible units of somewhat larger volume; 

 the placement of the "C" battery supply in a separate compartment 

 provided with a switch and meter jack, permitting rapid measure- 

 ment of critical voltages; two trickle chargers for the 6-volt "A" 

 batteries, provided with rate-of-charge meters; and a cell holder 

 designed to accommodate as many as four 10 cm. semimicroabsorp- 

 tion cells. 



INTRODUCTION 



Certain modifications of many 

 kinds of commercial instruments are 

 required for their most effective use 

 on an oceanographic vessel. Among the 

 most troublesome conditions with which 

 one must cope on a research vesselare 



(1) corrosion by salt air and moisture; 



(2) roll, pitch, vibration, and other mo- 

 tion of the vessel; and (3) general lack 

 of time and space for complex mainte- 

 nance and repair procedures. Coping 

 with these difficult conditions at sea 

 has led the authors to make a number 

 of nnodifications in the Beckman Model 

 DU Spectrophotometer which improve 

 the reliability of operation and simplify 

 maintenance. Such modifications have 

 been made on two Model DU Spectro- 

 photometers, and these instruments 

 have given excellent service on several 

 expeditions and cruises during the past 

 2 years, 



DESCRIPTION OF MODIFICATIONS 



Desiccant Holders 



The moist air encountered on a 

 vessel in a nonair-conditioned labora- 



Note. --Robert W. Holmes, Assistant Research Biol- 

 ogist, and Robert J. Linn, Senior Marine Technician, Scripps 

 Institution of Oceanography, La Jolla, California. 



tory requires a frequent change of 

 desiccauit, especially in the phototube 

 housing. In this latter unit, desiccant 

 changes are required every 3-5 days 

 when operating in the tropics and some- 

 what less frequently in more northern 

 latitudes. The desiccant holders pro- 

 vided with the instrument are difficult 

 to fill; e.g., to change the phototube 

 housing desiccant, the cell compart- 

 ment must be detached from the photo- 

 tube housing and the back plate of the 

 phototube housing unscrewed to gain 

 access to the desiccant holder. 



These difficulties have been reme- 

 died to a large degree by the construc- 

 tion of two transparent plastic, 

 perforated tubes which maybe screwed 

 into receptacles mounted on the instru- 

 ment. Silicone grease-coated O-rings 

 serve as moisture seals in these units. 

 The top of the desiccant cartridge used 

 in the phototube house is made light- 

 tight (this is not necessary with the 

 other desiccant unit); inspection of 

 desiccant condition is made by un- 

 screwing the cartridge in the phototube 

 house --an operation that requires only 

 a few seconds. Desiccant in the car- 

 tridge is removed by loosening a plastic 

 cup which is inserted in the bottom of 

 the plastic cartridge. In figure 1 these 

 cartridges are shown mounted in posi- 

 tion, and in figure 2 a close-up view 



