ANALYTICAL EDITION
May, 1945
285
COPPER SOLUTION EXIT
U k e J l U a J k--TRANSFORMERS J --ABSORPTION
CELLS
FHOTRONIC CELL
L-
VARIABLE TRANSFORMERS TO RECORDER
TR ANSFORMER
c
Figure 2.
Vertical Section of Photometer Unit
I During t,he firkt 30 niiiiuteh thcri. K:L:I gr:tdual decrease in sensitivity, known as fatigue ( I ) , :ift er which the reading \vas practically constant for over 40 lioirrs' continuous operation. '&'hen the illumiiiatioii was inciwsecl from 40 to 1 0 0 ~by o removal of the screen, a n r w fatiguv t * t ' t ' t w w n a observed Tliich again became constant ~ . i t h i n30 niiuutes. \Vhen the illnmiriation was diminished from 100 t o 10y0by replacement of the screm, the sensitivity of tlie pliotoccll was fouiid to be slightly lo\srr tlisrn it had been w i t h coiistarii 40To illumination, but { v i t t i i i i 15 minutes tlic: sensitivity had r('turned I O the original v:ilutt. The faifigueeflert thus t n have :L characteristics v d u e for constitnt operation at each int istisity of illumination. -4s the change in fatiguc, occurred oii1.1~ in the first 30 minutes 2iftt.r a vhange in illuinin:ttion, the ( " ~ ) r introduced by fatigue was cowitlered minor i n the inrasureineiit ( I t ' t rmsmission through the oopper polutiori in which t.he c-hnnge.; iti concentration of bivalent copper arc rt:lstivcly s l o ~ . Tlits coiistancy of the record ov('r :t 40-hour intervd sliowed not only thnt thc. fatigue effert wan constant but also t h a t tlir illumination froiu tiie lamp was cowtani. ~ ~ i Jw c : of a sccoticl ph(JtoCel1 t o (,onipens:iie for fluctuatiotis in illnrnination thrrtsforc. \v:w consirlercd unnecessary. 10% o t 1hc full scale rt3:tcIiiig.
the ammonia-synthesis plant four sampler; of copper soluflow continuously through the analyzer and then return t,o Ihe plant. system. The four photometer units (photocell, absorpriori cells, lamps, &volt and variable transformers) and the volt:rge st,abilizer are mounted in a cabinet. The recorder and foul, hie-adjustment rheostats are mounted about 30 feet a,way froni I he photometer cabinet, at a place convenieiit for the plant operaI ors. The scale on the recorder is calibrated directly in terms of grams of bivalent copper per liter, using chemical analysis as thc -t;iridartl. To avoid making a separate calibration for each ab-irrption cell, tlie light transmission through each cell is assumed to iw proportional to the same empirical function of conrent,rwt ion. Thi? assumption permits a very simple procedure to IJ(% tolI(i\ved in rc:ading and maintaining the instrument, tinct i t wirstv n o errors larytx t~tiouglito prewiit wtisfartory mntrol ril Ilit, plant operations. The accumulation of precipitated material in the absorptioii (.r chart,, f:irilitates close control of p h i i t operation. The photometer and concentric ahsorption call described may be ust:ful in continuous transmission rtvordiiig of the cornposition of o t h w solntions, vspc illy t , h o s f ~of low t rar1sp;trctnc*y.
ACKNOWLEDGMENT
authors are grateful to J . G. Dely, consultant to the T V h , \sIiuhe suggestions initiated this work and t,o the staff of the cont,rol laboratory who devised the proccdure for maintaining tht: iristrunicmt in roritiniroiis oprratiou. 'rli(8
LITERATURE CITED ( I ) I ~ i i g c ~13.. . "Photoelenieiit~", t r . t)g h. St,. John. S c n . T n r k . Ileinhold PubliJhirig Corp., 1938. ( 2 1 bliller, M., and Junkitis, J . N..Chem. C@ . V e t . E r ~ g .50, , So. 11.
