is not a necessity except in the demonstration of Boyle's Law.

The activated charcoal ampule C is made from a piece of 25-mm. pyrex tubing 200 mm. long. It is filled with granules of 6 to 12 mesh activated coconut charcoal, on top of which is a small loose wad of glass wool, to prevent the cliarcoal granules from being blown into the glass manifold when the charcoal am- pule is allowed to warm up from the liquid air tem- perature. The charcoal ampule is .connected with a safety manometer by means of G-mm. pyrex glass tubing. The bottom of the charcoal ampule is ap- proximately 35 cm. from the base of the ring stand to insure enough room to raise and lower a liter Dewar flask around the ampule. An iron ring with a wire gauze serves well as an adjustable support for the Dewar flask.

USE OF THE APPARATUS

A word of caution should be given relative to the use of the activated charcoal ampule. Always open the stopcock H connecting the charcoal ampule with the system nery slowly. Failure to do so will result in a pressln-e surge in the manometer which will in turn cause the mercury in the right arm of the manometer to flow into the manifold. The reason for the low connection of the manifold to the absolute manometer is to keep the volume of both as small as possible.

Also, when the charcoal ampule warms up on re- moval of the liquid air the adsorbed air will be re- leased. Consequently, the pressure in the safety manometer of the charcoal ampule will increase until it is slightly greater than atmospheric pressure. At this point, the released air will bubble through the mercury. If desired, this can be prevented by sealing a stopcock onto the tube connecting the charcoal ampule and stopcock H.

( A ) Barometer. A demonstration of a method of reading a barometer is made by closing stopcock G and opening the two-way stopcock H to the atmos- phere. The level of the mercury column in the left arm of the barometer is read on the meter stick and

allowing ampule A to fill with air to any desired pres- sure by opening stopcocks E, G, and H to the atmos- phere. Stopcock F should he closed. When the de- sired pressure is obtained, stopcock H is closed and the pressure of the air in ampule A is read on the absolute manometer D. The temperature of the ampule is as- sumed to be room temperature which is read on a ther- mometer hanging near the ampule. The new tem- perature is obtained by raising a glass cylinder around ampule A and filling it with water and cracked ice. Within three minutes, no further reduction in pressure is noted. Typical data are:

Pressure, Tem#~roiws , Cm. 'K.

Initial Final (expt1.) Final (ealc.)

(D) Boyle's Law. Boyle's Law can be demon- strated by filling one of the calibrated ampules ( A or B) with air to any desired pressure and then evacuating the other calibrated ampule and the connecting glass manifold. Then the two ampules are connected and the new pressure is read. The new volume is the sum of the two calibrated ampules plus the varying volume of the glass manifold. For this reason the connecting tubes are as short as possible and are made of capillary tubing. The volume of the manifold and of the right arm of the absolute manometer is small compared with the volume of the two calibrated ampules. The average diierence between the experimental and the calculated pressures is of the order of 1 mm. However, by ex- pressing the pressures to the nearest centimeter the theoretical and the experimental values will check sufficiently well for lecture demonstration purposes. Typical data are:

Inilia1 Find Inilia1 Volumc, Volume, Prcrrurc, F i n d Prcrnrrc, Cm.

Mi. MI. Cm. Erpll. Colc.

then the level of the mercury column in the right arm of the barometer is read. The latter value is sub- tracted from the former to give the atmospheric pressure. Since no vernier scale is on the meter stick, the pressure is read to only half a millimeter.

(B) Adsorfition of Gases by Activated Charcoal. The use of 6 to 12 mesh granular activated coconut char- coal in an ampule immersed in liquid air as a source of a vacuum demonstrates the adsorption of gases by activated charcoal. This is most vividly shown by fill in^ the a ~ m r a t u s with air to atmos~heric Dressure

( E ) Dalton's Law. The procedure for this demon- stration is the same as that described for Boyle's Law with the exception that the second calihrated ampule is not completely evacuated, but instead filled to some definite pressure. With stopcocks E and F closed, the connecting glass manifold and absolute manometer D are evacuated, and then upon opening stopcocks E and F of the two ampules the new volume is obtained and the new pressure read. Data for a typical demon- stration are:

by oiening cocks E, F, G, and H to the atmosphere. ~ m p i r i c A Ampuic B

The system is then connected to the charcoal ampule rnitialvol 753 Initial volume. 925 ml.

by turning slowly stopcock H. The diminution in pina1 V O I ~ ~ ~ , 1678 F ~ ~ ~ I V O I U ~ ~ , 1678 m ~ . Initial Lrersure. 53.5 Em. pressure accompanying the adsorption of the air by 2 ~ ~ ~ ~ F , " ~ ~ i i , " f ~ ~ g r e , 29.2 em. Calculated partial prerJure, 29.5 em.

the cold activated charcoal is easily seen on the ab- partial ampule A + partial pres.ure of B = final pres-

solute manometer D. sure 29.2 cm. f 29.5 em.

( C ) Gay-Lussac's Law. This law is illustrated by - 58.7 em.

Observed final preravre = 58.3 em.

( F ) Vapor Density and Molecular Weight Deter- minations. Ampule B is evacuated, removed from the apparatus a t the standard taper conical joint K, and weighed on a balance with a counterpoise. It is then replaced on the apparatus and the connecting manifold is evacuated. Ampule B is then filled with the gas whose vapor density and molecular weight are to be determined. It is recommended that no gas be used which will attack the mercury or which might hydrolyze to yield products which would attack the mercury.

In the case of diethyl ether, which serves nicely, a little ether is poured into a test tube which has a one- hole stopper in it, connected by pressure tubing with tube J of the apparatus. A container with a little powdered dry ice is placed around the bottom of ampule A, which has previously been evacuated, and a little of the ether is condensed into the ampule. Stop- cock H is then turned to connect the vacuum with ampule A and any remaining air is removed, as in- dicated when the pressure on the manometer is equal to the vapor pressure of the ether a t dry ice tempera- ture. Then stopcock H is closed and stopcock F opened, connecting ampules A and B. The dry ice is removed from around the bottom of ampule A and the ether allowed to boil into ampule B until the pressure is equal to the vapor pressure of ether a t measured room temperature. Stopcock E is closed and the pres- sure of the gas in ampule B is read. Ampule B is re- moved from the apparatus and reweighed. Knowing the volume of ampule B, the pressure of the gas, the temperature of the ampule, and the weight of the gas in the ampule, the vapor density and molecular weight of the gas can be calculated.

Using some unpurified reagent shelf diethyl ether the following data were obtained:

Volume of ampule B = 925 ml. Pressure of gas in ampule B = 36.9 nn. of Hg. Room temperature = ampule B temperature = 24'C. =

"""0.7 ,3u, -. Weight of gas in ampule B = 1.336 g.

Volume of gas corrected to standard conditions = 0.413 liter Calculated k p o r density = 3.23 g./l. Calculated molecular weight from experimental data = 72.4 g. Theoretical molecular weight = 74.12 g.

(G) Vapor Pressure. The diethyl ether introduced into ampule A in the above paragraph may be used to show the relationship of vapor pressure and tem- perature by allowing the liquid ether in ampule A to warm up from the dry ice temperature to room tem- perature. As the ampule warms up the mercury level in the left arm of the absolute manometer rises and demonstrates vividly the increase in vapor pressure accompanying increase in temperature.

Owing to the impurity of the sample, the approxi- mate temperatures afforded by the air and by water baths, and to the lack of time allowed for complete thermal equilibrium to be established, it is best to read the pressures in centimeters of mercury. For unpuri- fied reagent shelf diethyl ether the following values.were obtained :

Tamparalnc, Vapor Prcrsurc, Cm. of Hz 'C. Expil. LiLmlurr*

* LANO=, "Handbook of Chemistry," 3rd ed., Hendbook Publishers, Ine., Sandusky, Ohio. 1939, 1194 pp.

( H ) Heat of Vaporization. he heat of vaporiza- tion may be conveniently shown by rapidly removing the diethyl ether, used to demonstrate vapor pressure, from ampule A . This may be done by connecting the source of vacuum with ampule A by opening stop- cocks E, G, and H. Due to the heat of vaporization, ampule A cools very rapidly to a temperature well be- low the dew point. As a result the moisture in the atmosphere condenses upon the walls of ampule A and eventually freezes. The frost is easily visible to the class.' -

~ D U T T ~ N , "Some lecture demonstrations," J. CHBM. EDUC.. IS, 15-7 (1941).