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 ampule is allowed to warm up from the liquid air temperature. The charcoal ampule is .connected with a safety manometer by means of G-mm. pyrex glass tubing. The bottom of the charcoal ampule is approximately 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.

allowing ampule A to fill with air to any desired pressure by opening stopcocks E, G, and H to the atmosphere. Stopcock F should he closed. When the desired 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 assumed to be room temperature which is read on a thermometer hanging near the ampule. The new temperature 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 demonstrated by filling one of the calibrated ampules ( A or A word of caution should be given relative to the B ) with air to any desired pressure and then evacuating use of the activated charcoal ampule. Always open the other calibrated ampule and the connecting glass the stopcock H connecting the charcoal ampule with the manifold. Then the two ampules are connected and system nery slowly. Failure to do so will result in a the new pressure is read. The new volume is the sum pressln-e surge in the manometer which will in turn of the two calibrated ampules plus the varying volume cause the mercury in the right arm of the manometer of the glass manifold. For this reason the connecting to flow into the manifold. The reason for the low tubes are as short as possible and are made of capillary connection of the manifold to the absolute manometer tubing. The volume of the manifold and of the right is to keep the volume of both as small as possible. arm of the absolute manometer is small compared with Also, when the charcoal ampule warms up on re- the volume of the two calibrated ampules. The average moval of the liquid air the adsorbed air will be re- diierence between the experimental and the calculated leased. Consequently, the pressure in the safety pressures is of the order of 1 mm. However, by exmanometer of the charcoal ampule will increase until pressing the pressures to the nearest centimeter the it is slightly greater than atmospheric pressure. At this theoretical and the experimental values will check point, the released air will bubble through the mercury. sufficiently well for lecture demonstration purposes. If desired, this can be prevented by sealing a stopcock Typical data are: onto the tube connecting the charcoal ampule and stopcock H. Inilia1 Find Inilia1 Volumc, Volume, Prcrrurc, F i n d Prcrnrrc, Cm. ( A ) Barometer. A demonstration of a method of Mi. MI. Cm. Erpll. Colc. reading a barometer is made by closing stopcock G and opening the two-way stopcock H t o the atmosphere. The level of the mercury column in the left arm of the barometer is read on the meter stick and then the level of the mercury column in the right arm ( E ) Dalton's Law. The procedure for this demonof the barometer is read. The latter value is substration is the same as that described for Boyle's Law tracted from the former t o give the atmospheric pressure. Since no vernier scale is on the meter stick, with the exception that the second calihrated ampule is not completely evacuated, but instead filled to some the pressure is read to only half a millimeter. definite pressure. With stopcocks E and F closed, ( B ) Adsorfition of Gases by Activated Charcoal. The use of 6 to 12 mesh granular activated coconut char- the connecting glass manifold and absolute manometer coal in an ampule immersed in liquid air as a source D are evacuated, and then upon opening stopcocks E of a vacuum demonstrates the adsorption of gases by and F of the two ampules the new volume is obtained activated charcoal. This is most vividly shown by and the new pressure read. Data for a typical demonfill in^ the a ~ m r a t u swith air to atmos~hericDressure stration are: by oiening E, F, G, and H to the atmosphere. ~ m p i r i cA Ampuic B The system is then connected to the charcoal ampule rnitialvol Initial volume. 925 ml. 753 by turning slowly stopcock H. The diminution in pina1 V O I ~ 1678 ~ ~ , F ~ V O~I U ~ ~ 1678 ~ ,I m ~ . Initial Lrersure. 53.5 Em. pressure accompanying the adsorption of the air by 2 ~ ~ ~ ~ F , " ~29.2 ~ em. i i , Calculated " f ~ ~ partial g r prerJure, e , 29.5 em. the cold activated charcoal is easily seen on the ab- partial ampule A + partial pres.ure of B = final pressolute manometer D. sure 29.2 cm. f 29.5 em. 58.7 em. ( C ) Gay-Lussac's Law. This law is illustrated by Observed final preravre = 58.3 em. USE O F THE APPARATUS

cocks

-

( F ) Vapor Density and Molecular Weight Determinations. 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. I n the case of diethyl ether, which serves nicely, a little ether is poured into a test tube which has a onehole 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. Stopcock H is then turned to connect the vacuum with ampule A and any remaining air is removed, as indicated when the pressure on the manometer is equal to the vapor pressure of the ether a t dry ice temperature. 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 t o 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 pressure of the gas in ampule B is read. Ampule B is removed 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 temperature by allowing the liquid ether in ampule A to warm up from the dry ice temperature to room temperature. 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 approximate 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 unpurified reagent shelf diethyl ether the following values.were obtained : Tamparalnc,

'C.

Vapor Prcrsurc, Cm. of Hz Expil. LiLmlurr*

*

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

( H ) Heat of Vaporization. he heat of vaporization 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 stopcocks E, G, and H. Due to the heat of vaporization, ampule A cools very rapidly to a temperature well below 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 ~"Some N, lecture demonstrations," J. CHBM.EDUC.. IS, 15-7 (1941).