An APPARATUS for DISPENSING DRY GASEOUS and LIQUID AMiMONIA CARL H. ALMFELT AND C. R. McCROSKY Syracuse University, Syracuse, N e w York
I
T HAS long been known that some salts deliquesce in the presence of dry ammonia gas. Ammonium thiocyanate and ammonium nitrate are salts of this type. Foote and Brinkleyl studied the ammonium thiocyanate-ammonia phase system and their work suggested to YoungZ the use of this salt as a convenient absorbent for the gas. I n his preliminary work on the study of the sulfides of ammonium this mixture served as a source of dry ammonia gas and was found to be more efficient than the ammonium nitrate-ammonia mixture. Later Scheflan3 found this mixture a convenient and reliable source of the dry gas in his study of the ammonia-hydrogen sulfide system. Briefly, the procedure consists of condensing ammonia gas from a steel cylinder on the dry ammonium thiocyanate salt a t the temperature of an ice bath. The salt melts, absorbing about forty-five per cent. of its weight of the gas. The mixture may be kept in an ordinary flask with a wired-in stopper a t room temperature. When the ammonia is used the ammonium Foors AND BRINKLEY, 1.Am. Chem. Soc., 43, 1178-9 (1921). lYou~c,unpublished Master's thesis. Syracuse University, 1921
SCHEPLAN AND MCCROSKY, J. Am. Chem. Sac., (1932).
54, 193-202
thiocyanate salt crystallizes, but may be used again by condensing more ammonia gas on the solid. EXPERIMENTAL WORK
After considerable experimentation the container illustrated in Figure 1 was devised and found to be efficient in dispensing dry ammonia gas from the ammonium thiocyanate-ammonia mixture. This flask readily supplies a few cubic centimeters or a large volume of the gas for the lecture table or other use, or very quickly a few cubic centimeters of liquid ammonia according to the method subsequently described. A considerable amount of work can be done with gaseous or liquid ammonia with such an apparatus before recharging is necessary. Furthermore the gas is dispensed a t a very moderate pressure; so different from the high pressure (involving manipulative difficulties) experienced when taking the gas directly from a steel cylinder. The following details are observed in charging the container illustrated in Figure 1. An absorbtion train of the type illustrated in Figure 2 is used. This apparatus consists of four one-liter flasks. Each is fitted with a two-hole rubber stopper, which, in the case of
"B," is wired to the flask. "B" contains three to five hundred grams of dry solid ammonium thiocyanate, and is cooled in an ice bath. "A" and " C serve as safety bottles; "A" to prevent any of the mixture in
flask "B" sucking back to the steel ammonia cylinder, and "C" to trap the water contained in flask "D." The water in flask "Dmis to absorb any ammonia gas which isnot absorbed by the ammonium thiocyanate. All of the flasks are connected by meansof rubber tubing. To prepare the solution a slow stream of gas is passed from the steel cylinder into flask "A," No gas will escape
from flask;"= for the first few hours. The solution is nearing saturation when gas begins to escape from "D." Flask "B" is then disconnected from the train, and the solution is transferred to the ~ermanentflask illustrated inlFigure 1. In order to do this the tube from flask "B" which extends to the bottom of the flask is connected to either stopcock~ofthe other flask as shown in Figure 3. Both
stopcocks of this flask, the permanent flask, are opened, and the short tuhe of flask "B" is closed. By slight warming of flask "B" the liquid is caused to flow into the permanent flask. The stopcocks in this flask are then closed, and the solution is ready for use. To recharge the flask it is only necessary to place i t in the train in place of flask "B." This now becomes a permanent apparatus for dispensing ammonia and can
be used over and over again. One-half pound of ammonium thiocyanate may serve to dispense conveniently in such an apparatus many liters of liquid ammonia or large volumes of dry ammonia gas, and the apparatus is convenient to keep in chemical stockrooms. With such a source of the gas more extensive experiments by students are possible. Pure dry liquid ammonia can be readily prepared according to the technic illustrated in Figure 4. The liquid can he condensed on any substance in the test-tube cooled in a carbon dioxide-ether mixture. Five to ten cubic centimeters can be collected in as many minutes. The testtuhe may be stoppered with a two-hole rubber stopper, one hole filled with a drying tube to prevent access of
moisture. The condensation may be observed by using a transparent Dewar flask to hold the carbon dioxideether mixture. In this simple way the solubility of substances and their behavior can be studied. qualitatively, in a fairly rapid manner.
