HIGHLY EVACUATED DEWAR FLASKS M A D E OF " P Y R E X " BRAND GLASS The evacuation of Mass Spectrometer Tubes for the Atomic Bomb Project necessitated our installing high vacuum equipment considerably advanced over any used commercially. This equipment now enables us to produce De wars having a vacuum and permanency heretofore considered unattainable in production. # Evacuation follows a procedure similar to that described by Scott, Cook, and Brickwedde in "Bureaa r Standards Journal of Research," Vol. 7, No. 5, Nov. 1931, entitled "Silvering όχΛ Evacuating of Pyrex Dewar Flasks." Degassed by baking under vacuum with liquid air traps in the line at slowly rising temperatures up to 500° C, and sealed off at a guaranteed vacuum of 1 X 1 0 - 7 mm of mercury, Martin De wars provide the best permanent insulation against heat transfer by convection. SILVERED
# Except for extra large or unusual shapes, no spacers are used between the walls. Heat transfer by conduction occurs only at the top seal between the inner and outer vessel; with "Pyrex" glass this is comparatively low, much lower than in any metal flask. # Silvering also follows the procedure of Scott, Cook, and Brickwedde. Clear, unblemished reflecting surfaces reduce heat transfer by radiation to a minimum. # M a d e of heavy "Pyrex" blown cylinders, with metal protecting base, Martin De wars should last indefinitely with normal care. While their first cost may be somewhat higher, they usually pay for themselves in a short time in saving of contained material alone.
UNSILVERED
# Available silvered, unsilvered, lower half silvered or third sil vered or strip silvered (silvered except for a clear, full length win dow front and back). May be had in cylindrical sizes up to 250 mm I.D. also with constricted neck, or spherical shape. A few common cylindrical sizes are priced here, all with metal base. I.D. mm 50 *68 t68 80 95 95 110 120 120 135 145 145
STRIP SILVERED
Depth mm 200 200 300 250 250 350 300 300 400 350 400 500
' So-called pint Dewar.
-Ξ^ο^^^^^άτ 1916-1920 3042
Capacity ml 330 650 950 1100 1550 2250 2450 2950 4050 4200 5600 7200
Silvered $ 7.75 11.00 12.00 14.50 18.75 20.75 24.50 29.00 32.00 35.25 43.50 48.50
Not Silvered $ 6.75 9.50 10.50 13.00 17.00 18.75 22.25 26.50 29.25 32.75 41.00 45.75
Half, third Silvered $ 9.00 12.75 14.00 17.00 21.75 24.00 27.75 32.50 36.25 39.25 47.75 53.00
f So-called quart Dewar.
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