CALIFORNIA INSTITUTE OF TECHNOLOGY
June 28, 1942
Professor Warren C. Johnson
Department of Chemistry
University of Chicago
I can now report progress on the carbon monoxide instrument. The lines of attack which I have though of have been
followed up, but have not so far come to anything. However, about six weeks ago I told Dr. Arnold O. Beckman, formerly Assistant
Professor of Chemistry in our Department, and now Head of the National Technical Laboratories, about the need for this instrument,
and about ten days ago he came ot me with an idea which he thought would work. He has now made further calculations, with
results that look very promising.
The instrument which he has in mind would work in the following way. Air would pass through a tube such that the
absorption of a beam of light through the air could be measured, then through a layer of heated iodine pentoxide, which would
be reduced by the carbon monoxide with formation of iodine. The air would then continue through another tube in which the
absorption of light could be measured. The change in light absorption in a region where iodine vapor is absorbing, as measured
by a split-element photovoltaic cell, would give the amount of carbon monoxide initially present in the air.
Using the 1936 data of Rabinowitch and Wood, for light with wavelength about 5000 Å, Dr. Beckman has calculated that
it should be practicable to detect the presence of carbon monoxide in quantities as small as ten parts per million, that is,
one thousandth of one per cent of an atmosphere. Larger quantities could presumably be determined with considerable accuracy.
This calculation is based on the use of a cell one meter long, which presumably could be a tube bent around into a circle,
with the light transmitted through it by internal reflection.
The volume of the apparatus as planned would be perhaps one-half cubic foot, its weight not over ten points, and
the power source any convenient supply, 6 or 12 or 110 volts. The instrument would indicate amount of carbon monoxide continuously,
and could be arranged to provide an alarm. The estimated price of the instruments in quantity production is a few hundred
I would be glad to know what the present situation is about a carbon monoxide instrument. If there is still the need
for the instrument described in your letter, I would recommend that Dr. Beckman be given a contract for developing an instrument
along the line which he has suggested. From the success which he has had with his pH meter and spectrophotometer, I would
expect him to do a good job.