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GETTi- I-!AL ELECTRIC CO: :?AKY Research Laboratory 1 River Rd. Schenectady, i`.Y. Oct. 11, 1940 Hr. George Calingaert, Director Chemical Research Laboratory Ethyl Gasoline Corporation Detroit, Michigan Dear Hr. Calingaert: Finally now I can answer your letters of March 4 and July 26 relative to the sensitivity of the mercury o.ctector to tetraethyllead. I have just completed a preliminary test using nitrogen as a carrier, .art of it going through three bubbling tubes in series and the rest of it acting ac a ciluter under measured conditions. This reined gas tent into the retry detector and was exhausted outdoors. The rough curve I obtained giving rcter reading versus concentration shots that 1/4 scale reading occurs at IOC parts per million by volume. Thi s would be linear up to approximately 3/4 scale reading ano would saturate to full scale at higher concentrations. The first observation to be made relative to this sensitivity is that I had no assurance that the gas was saturated after leaving the bubbling tubes, especially with the snail amounts of tetraethyllead in these tubes. In the second place this concentration need not be taken as a sensitivity limit due to the possibility of expanding the scale by a factor of at least 10. A further observation which. I have not yet satisfactorily answered is that there is a residual reading of the meter after passing the lead mixture through the detector and scavenging it with uncontaminated gas. This residual reading nay be as high as 30"' of the test reading. One possible reason for this may be the deposition of lead or a compound on the phototube or U7 lamp cue to activation by the 2537 a radiation. I have tried wiping the tubes with a water-moistened cotton pad vdth no success. If the sensitivity of the detector as I have just given it is of the right order of magnitude for your use and if .you are still interested, further tests should be conducted for which I shall need at least 100 cc. of tetraethyllead. Very truly yours T .T.V.codscn :Y; cc/jh (signed) T. T. 'codson Ke 0022879