Document rpXY7LyrLjrzoLwaBM6N9ppze

Anniston COPT Copy:. hfr, L. C. Oarrett (3) . i - MONSANTO CHEMICAL COMPANY ' J Dr. N. N. T. Samaras Springfield, Massachusetts ) Mr. R. D. Dualop , Dr. L. Nielsen Miss R. Levresult September 17, 1946 Dr. R. L. Jenkins LIQUID DIELECTRICS v y-y y7* fr/;.y/y-yv' '' 5 Dr. Samaras has asked me to reply to your letter of September 10 ooncernlng the ;i, .standardization of your equipment.for determining poser factor, and dielectric con- We recently had occasion here at Springfield to construct and calibrate a cell for . . . liquid dielectric measurements. Thlfftjgtene-free benzene makes 5an ideal standardizing fluid in many ways* It has a very low power factor (about 0.04$) and a dleleotrlo oonstant which has been determined with high precision*..^yFurthermbret-'.'l'ts .dleleotrie properties vary only slightly with temperature* The International Tables give - . 2.283 0.002 for the dielectric constant of pure benzene at 20*0. and the tempera ture coefficient is listed as minus 0.001 per degree 0* 41 y, .As an alternative to benzene, one could use m-xylene^ which has the following \ characteristicsyyy-y ' PPpy f-' .$ - . . /' k (at 20*C) - 8.374 y' dk w -0,0019 per degree 0 By means of one capacitance measurement with one of the above standardizing liquids as dielectric and another with air as dielectric (empty cell), it is possible to calculate the cell constant* . . ' . `- For empty cell (empty) C (cell const*) '*(^2. ^ea8) ^ t> /<s ~ For cell filled with benzene at 26*0. - 0^ (Benzene) 2.277 0 (cell const*) 0^ (leads) ^ ^ These two equations may be solved simultaneously for the two unknowns - C, the cell oonstant and 0^, the capacitance of the leads* The dieleetfic oonstant of an un known liquid, x, is then . . y'.. \ ' . \ - , -y- ' '/< W|^J:y*here Cx ftp- y`:*'r is'tha^measurea kX...- Cx n 0, ,1 * capacitance witM the colX filled V,v ar ^ V w with the unknown, and and C have the &uae meaning "as before. r .<' y > ; --V; x-'-yP / Mc- We use a small coaxial-cylinder type of cell which has a cell constant of 37.6 mmf. ~ and lead capacitance of 1.2 mmf. We found it necessary to gold plate the cell electrodes in order to minimize electrdytic effects. If you would find it more convenient to send us your cell for calibration, we shall be glad to do so. I know of now liquid with low power factor and dielectric constant of about 4 which could be used simply as a comparative standard, but see no necessity for such standardization if the cell is dimensionally stable and the measuring equipment reliable. . .......... /pec AB 9/25/45 D. Telfair DSW 331115 STLCOPCB4077759