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 10cm. 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 aresearchvesselare 
(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 modifications 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 
desiccant, especially in the phototube 
housing. In this latter unit, desiccant 
changes are required every 3-5 days 
when operating inthe 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 may be screwed 
into receptacles mounted onthe 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 
