1882.] On an Instrument for Correcting Gaseous Volume. 167 



wards to exclude dust ; the other tube terminates in a bulb, whose 

 capacity is about four and a half times that of the tube. The two 

 tubes are connected below by means of caoutchouc tubing with a 

 small cylinder containing mercury, closed above by a leather cap, 

 which can be pressed down by a button attached to a screw moving in 

 a fixed socket. When the screw and button are lowered the mercury 

 rises in both tubes. The ends of the tubes and the reservoir of 

 mercury are contained in a square box, upon the bottom of which they 

 rest, and whose top carries the socket in which the screw turns. 

 At the back of the box is a wooden upright which supports the 

 tubes. The tube which terminates in a bulb is graduated and figured 

 so as to mark the capacity of the bulb and tube, down to each line 

 of graduation. 



In technical measurements of coal gas it is still customary to take 

 for the standard conditions an atmospheric pressure equal to 30 inches 

 of mercury and a temperature of 60° F. The instrument here figured 

 has been made for correcting to these conditions. The capacity of the 

 bulb and stem down to the first line is 3*1 cub. centims., and that of the 

 graduated portion of the stem is 0*7 cub. centim. The bulb and stem 

 have been charged first with a minute drop of water and then with a 

 quantity of air, occupying under standard conditions 3^ cub. centims., 

 the stem below this level being filled with mercury. This volume 

 is marked on the instrument as 1000, the unit taken being, cub. 

 centim. The top line of the graduation marks a capacity of 3'1 cub. 

 centims., and is figured 930, this being the smallest volume to which 

 the inclosed air is likely to be reduced by low temperature and high 

 atmospheric pressure. The maximum volume to which the inclosed 

 air is likely to be expanded may be taken at 3*8 cub. centims., and 

 accordingly the lowest line of graduation marked on the stem is 1140. 



To use the instrument the pressure of the screw on the mercury is 

 increased or relaxed until the level of the mercury is the same in 

 both tubes. A reading is then made on the graduated stem, and 

 represents the volume occupied at the actual atmospheric pressure 

 and temperature by a mass of air in presence of water which, under 

 standard conditions, occupies a volume 1000. Any volume of gas 

 measured in a gasholder or registered by a meter, under the same 

 conditions, may be corrected to its true volume, under standard con- 

 ditions, by multiplying by 1000 and dividing by the number read upon 

 the instrument. 



When the standard conditions adopted are 0° C. and 760 millims. 

 pressure the bulb is made somewhat larger, so that the 1000 gradua- 

 tion comes near the top of the stem, and the graduations are continued 

 downwards to 1230. 



The name proposed for this instrument which serves to correct the 

 measure of a gas, is aer orthometer. 



