. Bulletin of the Department of Agriculture. Agriculture; Agriculture. BULLETIN 1022, U. S. DEPARTMENT OF AGRICULTURE. ^S& METHODS AND APPARATUS. DETERMINATION OF PRESSURE. In the pressure and vacuum studies, preliminary experiments soon showed that the pressure and vacuum gauges commonly used were too coarse and inaccu- rate for careful work. Because of their me- chanical construction they are always open to the danger of be- coming weakened, which makes frequent standardization neces- sary. They also seem abnormally sensitive to barometric pressure, for which corrections are difficu
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. BULLETIN 1022, U. S. DEPARTMENT OF AGRICULTURE. ^S& METHODS AND APPARATUS. DETERMINATION OF PRESSURE. In the pressure and vacuum studies, preliminary experiments soon showed that the pressure and vacuum gauges commonly used were too coarse and inaccu- rate for careful work. Because of their me- chanical construction they are always open to the danger of be- coming weakened, which makes frequent standardization neces- sary. They also seem abnormally sensitive to barometric pressure, for which corrections are difficult. Their use in this work was there- fore abandoned except in certain rough tests mentioned below, and in their place a special mercury manometer was substituted. Fig- ure 1 illustrates the manometer. This manometer consists of two glass arms, A and B, which are connected by a flex- ible tube (C) of rubber pressure tubing rein- forced with closely wound copper wire to minimize expansion. A scale Z>, so gradu- ated as to allow read- ings in both directions from 0, is so placed that the zero mark stands at x of the glass arm A, which repre- sents the constant level of the mercury in that arm. The flexible tube E, which is identical in structure with (7, connects with an air-tight iunction. EXHAUST Fig. 1.—The manometer used in the pressure-vacuum tests. A, Fixed glass arm of the manometer; B, movable glass arm; C, flexible rubber tube wound with copper wire connecting glass arms A and B; D, scale, graduated in centimeters or inches; E, flexible rubber tube wound with copper wire connect- ing manometer with the can-sealing device; F, test can ; R, steam retort; T, thermometer; 0, zero mark on the graduated scale; X, mark on glass arm A corresponding with the zero mark on the scale D, at which the mercury column in A is held constant. The plus and minus signs on the scale indicate the portions of the scale above and below the zero mark, Please note that these i
Size: 1154px × 2165px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauth, bookcentury1900, bookdecade1910, booksubjectagriculture
