The Scientific War Work of Linus C. Pauling Narrative  
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Building the Meter
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It was two weeks before Pauling received a response. During that time, he had set Wood and Weinbaum to verifying and reworking calculations in an attempt to build a strong theoretical platform on which to build the apparatus. Once done, Wood began the construction of the meter. On October 22, Chadwell mailed a letter to Pauling appointing him "official investigator" for the project. The project was assigned a budget which included funding for Wood's salary, a temporary assistant, materials, and equipment for a six-month probationary period. By November 1, Wood had completed the model and run a battery of tests on it. Though fragile and prone to decalibration, it worked.

The apparatus was based on the principle of a torsion balance, a measuring device originally developed by Charles-Augustin de Coulomb in 1777. Wood created the balance by attaching a tiny metal bar to a quartz fiber. He then attached a hollow glass sphere to each end of the bar and adhered a mirror to the fiber crossbar. The entire device was then strung between the points of a standard horseshoe magnet which surrounded it with a magnetic field, and was then placed under the protective walls of a bell jar. When the spheres were filled with air, the paramagnetic forces present in oxygen atoms would cause the dumbbell setup to rotate, twisting the quartz fiber. The mirror on the fiber, as it twisted, would alter the angle of a reflected light beam, striking a photocell. The photocell readings would then register on a dial, giving an approximate measure of present oxygen levels.

Pauling contacted Chadwell, declaring success but he and his researchers were in need of information. They had developed a working meter – a prototype – but had little idea of the conditions under which it would be used. Problems of weight versus accuracy, resistance to acceleration and vibration, balancing, movement and inversion were variables Pauling had not had an opportunity to account for. The NDRC was operating under a strict need-to-know basis and, as a result, Pauling had been working blind. Fortunately, Wood's work in the laboratory was enough to earn Pauling access to confidential information. The instrument, he was told, would need to be usable despite frequent acceleration and deceleration, tilting on all axes, and constant shock and vibration. In short, the fragile instrument needed to be indestructible. Confronted with this challenge, Pauling and Wood returned to the laboratory. There, they designed an adjustable support for the apparatus which allowed it to remain stable despite movement and shock. Shielding and damping techniques were developed too, allowing the meter to give accurate readings under moderate strain from outside forces.

There were, of course, setbacks. The quartz strand suspensions used in the instrument were procured using a micromanipulator, a tool operated with a physical input device - often a joystick - allowing for controlled, precise movements. Unfortunately, after only a few months of research, the borrowed micromanipulator at Caltech was returned to Cambridge, forcing Pauling's lab to construct another, thereby delaying progress on the oxygen meter. The quartz fibers themselves were nearly invisible to the naked eye, making the torsion assembly remarkably tedious. The glass balls used on the instrument were equally problematic: they had to be hand-blown but they were so delicate that only one graduate student could successfully create them. Even then, it took many tries - sometimes hundreds - to create a single perfect bulb. Supplies, too, were difficult to acquire. Liquids for damping, metals, and magnets all proved hard to find, further slowing the research process. Perhaps worst of all the impediments, however, was Pauling's deteriorating health.

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See Also: Letter from Linus Pauling to T. K. Sherwood. February 8, 1941. 
See Also: Letter from Linus Pauling to T. K. Sherwood. May 13, 1941. 

Click images to enlarge 

Torsion balance used in the Pauling oxygen meter. approx. 1945.

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Notes by Linus Pauling related to the development of a torsion balance for the Pauling oxygen meter. October 1940.

"Have most promising method determination partial pressure oxygen. Best available post-doctorate assistant offered job elsewhere. May I hold him. Please telegram or telephone."

Linus Pauling
October 8, 1940
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