. Chemical Instrumentation
Topics in..
I
I small units primarily for student use (Cenco), but one finds no mention of direct readers. Accessories are available in prafusion-densitometers, arc and spark sources, electrodes, film processors, plotting boards, etc. The transition to photoelectric methods in spectrophotometry is evident. The now obsolete rotating sector attachment (Fig. 2) to adapt a spectrograph to photometry was still in use (Hilger's "Spekker" and an old Keuffel and Esser unit are described), as were visual spectrophotometers (Konips-Marten, B. & L.. Hilger) (Fig. 3). But photoelectric instruments are also present. The General Electric (Hardy) model, Mdler says, was introduced "some years ago." Also described are the Cenco Spectrophotelometer, using a barrier-layer cell for visible range measurements, and the Coleman Double Monochromator Spectrophotometer. The latter was ahead of its time in combining prism and grating dispersion. Its photocell output was balanced by means of manual adjustment of a dec(Continued on page A392)
Edifsd by GALEN W. EWING, Seton Hall University, So. Orange, N. J. 07079 These articles are intended to serue the readers o f ~ m JOURNAL s by calliny allention to new developmenls i n the theory, design, or availability of chemical laboralory inslrumentalion, or by presenting useful insighla and ezplanations of topics that are of praclical importance to those who use, or Leach the use of, modern instrumenlation a n d instrumental techniques. The editor invites correspondence from prospeclive conlribulors.
LXXII. Analytical Instrumentation: 1940-41 Vintage Galen W. Ewing
SPECTROSCOPY
The late Ralph Holcombe Muller made many invaluable contributions to American laboratory instrumentation. Most of my readers will remember his monthly "Instrumentation" column in Amlytical Chemistry, in which he described current developments and with unerring judgement pointed out the significance of innovative features. Not the least of his contributions was a pair of articles in the Analytical Edition of Industrial and Engineering Chemistry ( I ) , constituting the entire October issues in 1940 and 1941. These articles, written a t the request of the editor, Harrison E. Howe, constitute a survey of laboratory instruments in the early days of the electronic revolution (2). Both issues contain many advertisements of instruments, some not specifically described in the articles. They also contain a Directory of Instruments and Related Apparatus, a forerunner of the present annuallabomtory Guide. The object of the present paper is to summarize the state of the field as it existed a t that time, for the interest of its comparison with today's vast array. I shall. for convenience. assume that the two articles describe the same status, and I will not document each reference thereto.
Many classical types of spectrographs are described, from large prism or prating instruments (Baird, B. & L., Dietert, Jarrell-Ash, Gaertner, Hilger) (Fig. I), to
Figure 2 Rotatng sector lor spectraphotometry Bausch & Lomb
('uuilrsy, Bau3ch i( Lo,mh Opriiai Co
Figure 1. Cornu type prism spectrograph, Bausch & Lomb.
Volume 51. Number 8. August 1974
/
A391
Flpure 3. Polarization typevisual specfrophotometer, Bausch 8 Lamb
ade resistor hank; the null condition was observed on a Coleman pH electrometer connected to the spectraphotometer by jumper wires (Fig. 4). The Beckman "Photoelectric Quartz Spectrophotometer" (National Technical Laboratories), subsequently known as the Model DU, was mentioned briefly in the 1941 article hut 'not in 1940. An advertisement in the 1941 issue (Arthur H. Thomas Co.) quotes $750 far this instrument for the ranae 320 to 11333 nm, without the storage battery. A footnote in small type indicates that it can be supplied far use in the "far" ultraviolet, with a hydrogen lamp and special phototube, no price quoted. Photoelectric filter photometers have always been popular, and several brands were available in 1940 (Aminco. Ceneo.
Figure 4. Coleman Double-Monochromalor Spectrophotometer, showing the pH electrometer used an null indicator.
Hiker, Klett, Leitz. Photovolt, WilkensAnderson) (Fig. 5). Man" of these have been discontinued since, but others have been introduced. Some (e.g., Klett) have persisted almost unchanged. Competition from the Spectranic-20 (B. & L.) was far in the future. G. M. Laboratories made a special-purpose filter photometer far vitamin A determinations. I t used a sodium arc lamp and a filter to isolate the 330.3 nm line, dual phototubes and a vaeuumtube amplifier; extinction (absorbance) measurements to a precision of +1 percent were claimed. Photovolt had a similar unit. Many visual "colorimeters" (better called comparators) were extensively employed in 1940. These include Duhoscq colorimeters by B. & L., Hellige, and Spencer Lens (Fig. 61, a neutral wedge photometer by Aminco, a polarization type by Leitz, and the Zeiss Pulfrich photometer (Fig. 7). A spectrophotometric titrator with a Mieromax IL. & N.) recorder, assembled in Dr. Miiller's laboratory, is described. Turhidimetry in 1940 could be measured in a very simple comparator (Clark, via R. P. Carpille), or in a Helliae or Pam turbidimeter. The latter measured the depth of a liquid column through which a small light bulb could just be discerned; it was made in visual and photoelectric models. Of course, an" filter photometer can serve as a turbidimeter. Several photoelectric fluorometers (Continued on page A394)
A392
/
Journal of Chemical Education
FRONT
rr
APERTURE P U T S
DIAL IN=
AMP
SLlDE WIRE CONTROL DIAL
SL1DE WIRE CONTROL DRIVE
PHOTOCELL
BSORPTION
b
n o w
REFLECTOR
I
A850RPT10N CELL HOLDER
COLOR FILTER CONTROL DIAL
ZERO ADJUSTER CONTROLKNOBS
UMP HOLDER
lTlONlNG DEVICE 'COLOR
BINDING POSTS
ZERO ADJUSTER POTEWTlOMETLRS
