C' equals the constant volume to lie tleterniined.
Solving
t h i.? - PITA c = Pgv? P, - PJ
Obviously, the accuracy of such a measureiiient is iiiver>e!y proportional t,o the \-oluiiie to be measured, and of co1ir.p it is assumed that the buret K has been accurately calibrated. ILLU~TRA OFTDEYIATIOSS IO~ FROM G4s Laws-The baroburet can readily be made the basis of an excellent experiment to demonstrate with such gases as carbon dioxide, sulfur dioxide, etc., the deviation froin the gas laws. Of course, the deviation with the so-called permanent gases is too small to be readily measured. DETERMIKATIOS OF VAPORPRESSLRE-TO determine the vapor pressure of a solid or liquid, the substance is placed in a bulb sealed to one of the capillaries connected to F using a baro-buret of the design shown in Figure 3. The buret is then used as the bulb of a Toepler pump, gas being pumped from the bulb into the buret, and by rotating the stopcock F 180 degrees and raising the buret the gas and vapor are driven out. Five or six punipiiigs are generally sufficient to give a constant pressure. The vapor tension is then equal to the difference in the levels of the mercury in B and K . The last application illustrates how the buret may be used as a Toepler pump t o pump out a small space. This *
idea has been applied in a number of ways n-hich will be dircussed in separate papers: notably t o a new method for gas to the accurate analysis of gases with new apparatus for the determination of adsorption 11y the static method: to an apparatus for the study of gas-solid equilibria in which pressure, volume, and concentration are measured; to the rapid determination of the density of gases; to the measurement of gases evolved from reactions at high temperatures; to the determination of the solubility of gases in liquids; as a laboratory dernoiistratioii of Ihyle's l a y to a inethod of obtaining accurate gas mixtures for the study of the critical phenomena of gas inixtnres: to the measurement of gases a t higher pressure>, etc. Literature Cited 1) Baume a n d Perrot, J . chim $ / ? y e . , 11, .57 (19133. ) Bone, Pvor Chem. S O L , 14, 154 (1898). ) Bone a n d Ivheeler, .I. .Tor. Cheni. I n d . , 27, 10 (19G8i. \ Booth and Jones, IND.ESG. CI%E>r., 19, 104 113371. ( 5 ) Booth a n d M c I n t y r e , I b i d . , Anal Ed.. 2 , 12 (1930). (6) Frankland a n d Ivard, J . Chem. Sot., 6, 197 (1854).
(7) Germann, J . . l m Chem. SO
