Clark and Weston standard cells . nt and inexpensive form of rheostat, where a sup-ply of incandescent lamps of various candlepowers is available, isshown in figure 8. The lamps in the two lower sockets determinethe external resistance during the cooling period. When the relaycircuit is open all the lamps are in parallel. Stirring:—Uniformity of temperature throughout the bath wassecured by an efficient centrally located stirrer producing an upwardand rotary circulation. In addition the rectangular stand on whichthe cells were mounted was provided with a sheet metal shieldextending to within 4
Clark and Weston standard cells . nt and inexpensive form of rheostat, where a sup-ply of incandescent lamps of various candlepowers is available, isshown in figure 8. The lamps in the two lower sockets determinethe external resistance during the cooling period. When the relaycircuit is open all the lamps are in parallel. Stirring:—Uniformity of temperature throughout the bath wassecured by an efficient centrally located stirrer producing an upwardand rotary circulation. In addition the rectangular stand on whichthe cells were mounted was provided with a sheet metal shieldextending to within 4 cm of the bottom of the bath (Fig. 6), thusdirecting the circulation and in addition protecting the cells fromthe direct influence of the cooling coil, and also in two of the tanksfrom the heating coils. Measurements made by a platinum ther- Wolff. IWaters. J Clark and Weston Standard Cells. 37 mometer showed that the temperature of the space occupied by thecells was everywhere uniform to well within °, so that it was ^ |. <3 1 s: C3 3 I I hardly necessary to employ a grid thermoregulator to integrate thetemperature of the bath. 38 Bulletin of the Bureau of Standards. \, The temperature variation during regulation is of course deter-mined primarily by the volume and differential cubical expansionof the liquid employed in the thermostat and the diameter of thecapillary. It is influenced, also, by temperature lag in the regu-lator and in the heating coils and by any contamination of the mer-cury surface at which contact is made. The lag is reduced by theform of regulator employed and by a proper adjustment of the exter-nal resistance, so that a minimum increase in the heating current isrequired for regulation. The actual range can be calculated as follows: Let Wx = rate of heat loss in watts during cooling periodIV% = added heating in watts for regulationtx = cooling period in secondst2 cheating Then wxtx=(iv-wx)t„ or tx + t,Hence Wx can be calculated. The
Size: 1331px × 1877px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., book, bookcentury1900, bookdecade1900, booksubjectcondensedmatter
