i 146
ARTHUR B.
iCoMMUNICATION FROM
THE
LAMB AND A . SPRAGUE COOIJDG~:.
RESEARCH DIVISION,c. w. s.,AND THE FIXED KITROGEN RESEARCH LABORATORY. ]
THE HEAT OF ABSORPTION OF VAPORS OM CHARCOALS1 BY ARTHUR E. LAMBAXD A . SPRAGCE COOLIDGE. Received March 28, 1920.
Introduction. In the study of the properties of active charcoal for use in gas masks it appeared of importance to determine the adsorption isotherms of a large variety of vapors upon charcoal, and the quantity of heat thereby evolved. It was soon found that the precise adjustment of adsorption pressure equilibria is very slow and exhibits irregularities apparently connected with the presence in the charcoal of minute traces of air and other impurities. The study of this aspect of the problem was, therefore, postponed, and attention was directed chiefly to the study of the amounts of heat evolved during adsorption. In these thermal measurements complete adjustment of the adsorption equilibrium is also slow; but at least a t low pressures, the greater portion of the gas is taken up in a few minutes, SO that accurate calorimetric measureiuents can be made quite rapidly by a suitable method as, for instance, that using the ice-calorimeter, provided the gradual adsorptiou of .the remaining vapor by the charcoal. be prevented. This can be done by closing off the system after an appropriate interval, close to the charcoal. The little residual vapor thus entrapped, even if it were completely adsorbed, could not evolve a measurable quantity of heat. Our general method of procedure was t o enclose in a glass tube, a weighed quantity of charcoal freed from gaseous impurities by evacuation a t a high temperature, place this tube in. an ice-calorimeter, and when constant readings had been obtained, to introduce a measured quantity of the vapor in question a t low pressure into the tube. We waited until most of it had been adsorbed, then shut the residual gas off from the charcoal, and finally observed the stationary reading of the icecalorimeter. This process could be repeated with fresh samples until an equilibrium pressure had been attained beyond which it was impossible to go without condensation of the vapor a t oo. Similar measure-. ments using an ice-calorimeter have previously be.en made on nitrogen, carbon dioxide and ammonia by T i t ~ f f . ~ 'I'he apparatus, materials and experimental procedure are first described; the results obtained and a discussion of them follow. Published by permission of Maj. Gen. W. I,. Sibert, Director, C.LV. S., C.S. Army. The authors wish gratefully to acknowledge their indebtedness to Margaret S . Coolidge for her skilful execution of a number of the measurements recorded in this paper. Z. physik. Chern., 74, 641 (1910).
REA?' OF' ABSORP'I'ION
OB VAPORS OK CHARCOAL.
1149
Apparatus. The apparatus used in these measurements presents certain advantages as compared with that used by 'X'itoff; it is shown in Fig. I . It consists essentially of the bulb R in which the gas or vapor is stored; the maiiometer €3 ; the ice-calorimeter C , and the valve D. The bulb A, together with the connecting tubes and the:partszof the manometer and valve which are occupied by gas, constitute the volume used in calculating the quantity of gas adsorbed. The temperature of the greater part of the system is given by that of the water a t room temperature which surrounds A ; that of the small volume represented by the valve, manometer, and conc: nections, will not differ sufficiently to cause appre2*o ciable err0r.l B serves as a manometer, ancl also as a valve to isolate the system from the pump (a Gaade mercury pump) so that the latter may be stopped or used for other purposes. The small sidetube a can be used as a simple MacLeod gage to indicate the vacuum atzaincd. A cathetometer is used t o read the manomwater etel-, ancl since it can be reIce lied on to only 0.05 mm., it is not necessary to employ refined methods of measurFig. I .--Adsorption apparatus and ice-calorimeter inn- the vacuum. We have r o t used a permanently exhausted manometer, because of the difficulty of cleaning and refilling. The one we used can be easily cleaned by emptying the mercury through b and pouring in cleaning solution by means of a funnel inserted through the filling plug p . The sample of charcoal is contained in the small bulb c, which can be instarted in an ice-calorimeter of the usual design. The latter is protected from heat exchange by immersion in a glass jar containing distilled water
B4
In a later form of apparatus, the large bulb was inverted and the connecting tubes all sloped to drain into E3 or D This was a great improvement, as meicury i i cwtain sooner or later to fly about in the apparatus, but with this arrangement it all riiti'i out agatn I n the old apparatus there was usually a little puddle of mercury 111 A , whose volunie had t o be estimated and corrected lor, and mhlch could bc removed
