202 ANALYTICAL EDITION Vol. 3. No. 2

Generator for Production of Carbon Dioxide of High Purity’

Edgar J. Poth

DEPARTXENT OF CHEXISTRY, UNIVERSITY OF TEXAS, AUSTIN, TEXAS

OR the production of a gas, such as carbon dioxide, it is often desirable that (1) its generation be effected F entirely within glass containers devoid of rubber con-

nections, (2) the apparatus be of such construction as to ad- mit a t the start of efficient removal of occluded gases, (3) the continuous or intermittent production of the gas in quan- tity and a t any desired rate be assured without an excess escaping into the laboratory, and (4) the gas be of uniform and maximum purity.

&though the apparatus herein described has been employed in the Texas Laboratory solely for the generation of carbon dioxide in connection with the estimation of nitrogen by the combustion method, the principle of construction can be adapted to the production of many other gases. It is ob- vious that, where desired, the gas concerned can be delivered free of water vapor.

In general there are two methods employed in generating carbon dioxide: the action of an acid on a carbonate or bi- carbonate, and the thermal decomposition of a bicarbonate. The first method is discussed by Bock and Beaucourt (1) at some length in a paper published in 1928. They cite sev- eral modifications to the routine of filling, as well as variations as to the form of Kipp generators, but finally conclude that the method of Pregel (3, 5 ) is the preferable one. Further- more, they conclude that the bicarbonate tube of von Brun- ner (3) can be made to yield a somewhat better grade of gas. But, owing to the fact that it must be swept free of air at each heating, the purity of the gas cannot be controlled as accurately as in the case of the Kipp.

Since that time the present author (4) has described a generator which enables one to store a quantity of carbon dioxide with complete assurance that it will represent a gas of a consistent high purity. After continuous use for a year this generator has fulfilled all claims advanced.

At times it is desirable to have an automatic or continuous generation of a gas. This feature is incorporated in the generator to be described. In its adaptation to the produc- tion of carbon dioxide, excellent results are obtained with the reactants 1:l sulfuric acid and a saturated aqueous solu- tion of acid potassium carbonate. The use of marble is in- advisable, because, in the author’s experience, it is not pos- sible to eliminate completely occluded air even after boiling out with water, treating with dilute acids, and pumping to a low pressure for several hours.

Construction and Operation of Generator

The accompanying figure is for the most part self-ex- planatory. A convenient design is with A and B made from 2- and 1-liter, round-bottomed, Pyrex flasks, respec- tively, A is charged with 500 grams of acid potassium car- bonate dissolved in 1200 cc. of water, and B with 170 cc. of water followed by 170 cc. of concentrated sulfuric acid. The heat of dilution raises the temperature of the acid almost

1 Received October 29, 1930. This paper is the outgrowth of an investigation of “The Nitrogen Compounds in Petroledm,” listed as Project 20 of American Petroleum Institute Research. Financial assistance in this work has been received from a research fund of the American Petrole im Institute donated by John D. Rockefeller This fund is being administered by the institute with the cooperation of the Central Petroleum Committee of the National Research Council

to the boiling point and thus contributes to the subsequent elimination of contained air. D and E are sealed, and the desired amount of water is introduced into the bubble counter, G. Then the T-shaped, three-way stopcock, .I, with its perpendicular arm, K , filled with and extending into mercury, is temporarily connected through rubber tubing a t I , and the entire system is evacuated with an oil pump simul- taneously through H and L. The pumping is continued for about 15 minutes when the appropriate amount of mer- cury is run into F. Both during the pumping and for some time afterwards, the bicarbonate solution in A will evolve carbon dioxide. Besides being a great help in sweeping out the last traces of dissolved air from the solutions, this property is used in starting off the generator. After closing the T- shaped stopcock, it is disconnected from the suction pump a t L. The evolution of carbon dioxide in A drives the gas into B to build up sufficient pressure to force acid into A

Figure 1-Generator for Production of Carbon Dioxide

upon evacuation through H . If H is closed immediately following the introduction of the acid, the gas generated will force more carbon dioxide into B. By repeating this pro- cedure, sufficient pressure can be built up in B to force the mercury seal, F. During this process, the T-shaped stop- cock is cautiously opened from time to time to ascertain when the pressure in B is equal to atmospheric pressure plus the height of the mercury column in F. When this is attained, the T-shaped stopcock can be removed, and the generator will deliver a stream of practically pure carbon dioxide when- ever H is opened. As the apparatus cools, or after it has stood for long periods of time, it may be necessary to apply suction at H and again force acid into A to reestablish the

April 15, 1931 INDUSTRIAL A N D ENGINEERING CHEMIXTRY 203

desired pressure in the system. Obviously, the basic prin- ciple of this generator can be adapted to the preparation of gases other than carbon dioxide.

(1) it is compact and is constructed entirely of glass without ground-glass connections; (2) it can be warmed and pumped free of occluded gases; (3) it is sealed with mercury against contaminating atmospheric gases; (4) it has a novel auto- matic feeding arrangement; and (5 ) it Utilizes its reactants

completely without wasting any of the gas produced, even during long periods of standing.

This generator incorporates the following advantages: Literature Cited

(1) Bock and Beaucourt, Mikrochemie, 6, 79 (1928). (’) Brunner* van* Chem*-Ztg.) s8r 767 (1914). (3) Hein, 2. angew. Chem., 40, 865 (1927). (4) path, IKD. END. cHIM., Anal. Ed., a, 250 (1930). (5) Pregl, “Quantitative Organische Mikroanalyse,” p. 98, Springer, 1930.

Improved Hydrogen-Electrode Cell for Determination of pH’,’

HE cell illustrated, de- veloped after experi- ence wi th numerous

types of electrometric appa- ratus, satisfactorily meets the requirements for rapid and accurate pH determinations on a variety of solutions and suspensions. The hydrogen electrode, calomel electrode, and salt bridge are readily constructed from usual labo- ratory materials a n d give service with minimum atten- tion.

A centrifugal circulator or stirrer which circulates a small constant volume of hydrogen through the liquid under con-

T W. B. Bollens

IDAHO AGRICULTURAL EXPERIMENT STATION, Moscow, IDAHO

The cell described, constructed from usual laboratory materials, is widely applicable for rapid and accurate pH determinations. Novel features are (1) a Pyrex- Alundum porous-tip calomel electrode, (2) a salt bridge giving sharp, reproducible liquid junctions, and (3) a stirrer which centrifugally circulates through the sample a small constant volume of hydrogen under constant pressure. The stirrer-circulator especially adapts the hydrogen electrode to solutions containing dissolved carbon dioxide or other gases participating in H-ion equilibria. I t also handles foaming liquids to advantage. Hydrogen saturation of the solution is eRected in minimum time and true H-ion equilibrium i s attained quickly. When side reactions interfere, voltage-time curves are useful in estimating the point of virtual H-ion equilibrium.

Typical data presented illustrate the rapidity, ac- curacy, and versatility of the apparatus.

stant pressure-is a feature of the hydrogen electrode devised for use with liquids containing carbon dioxide or other gases participating in H-ion equilibria. It is especially applicable to pH determinations on solutions or suspensions of alkali soils containing carbonates. In such cases colorimetric methods as well as the quinhydrone electrode are often in- applicable, while the use of a bubbling-type hydrogen elec- trode results in removal of dissolved carbon dioxide with consequent shift in acid-base equilibria and increase in pH. Shaking electrode vessels of the type described by Clark (3) and Snyder (6) may be used, but their construction is beyond the skill of ordinary glass blowers and the mechanism for shaking is more complicated than that required for the stirrer. Since the stirrer effects hydrogen saturation of both solution and electrodes in minimum time, its general application is indicated.

By using the stirring electrode with a modification of the salt bridge designed by Waterman (7), the advantage of permanent contact, together with a sharp reproducible liquid junction permits readings a t any time, whether the stirrer is in operation or not. It is thus possible to follow the volt- age change during a determination from the beginning until a constant or maximum value is attained This not only saves time but also permits a comprehensive voltage curve for guidance in determining the point of H-ion equilibrium.

Received August 8, 1930. f Published with approval of the director of the Idaho Agricultural

* Now associate bacteriologist, Oregon Agricultural Experiment Sta- Experiment Station as Scientific Paper 63.

tion, Corvallis, Ore.

Construction of Hydrogen Electrode

The stirrer-circulator con- sists of a small glass T-tube fused to a glass rod or shaft of similar diameter. An axial opening, corresponding in size to the bore of the tubing, is provided in the T where it joins the shaft within the vessel. Another opening is provided in the center of the open-end cross tube at the bottom. A hard rubber bear- ing for the shaft is centered in a sulfur-free rubber stopper that has been carefully filed or ground on the lower two- thirds of the circumference

to remove the taper and make a tight fit with the mouth of the vessel. Careful fitting of this stopper is essential; even a slight taper will result in its working loose when in contact with alkaline solution. The bearing should be accurately turned and drilled in a lathe, the upper half being drilled a few tenths of a millimeter oversize, so that the shaft fits with minimum play consistent with free operation. A shoulder for contact with the top surface of the stopper is provided for stability,

To hold the stirrer in place and to connect with the flexible shaft of a motor drive, a flexible coupling is made from a short piece of glass tubing fitted with a section of heavy-walled rubber tubing inside and projecting slightly beyond the upper end. The glass tube is of such inside diameter that it will rotate smoothly when slipped over the upper part of the hard rubber bearing; the rubber tube must fit snugly inside the glass tube and also hold firmly the driving end of the flexible shaft and the driven end of the stirrer shaft. Assembly is made by placing the coupling over the bearing and thrusting the stirrer shaft through the bearing and into the rubber tube inside the glass. To connect with the motor, the free end of the flexible shaft is brought into proper position and in- serted in the upper end of the coupling.

The rubber stopper must be carefully bored to carry not only the stirrer bearing but also a hydrogen inlet tube and the hydrogen electrodes. Two of the latter are always used and connected to a double-throw switch so one may be checked against the other during every determination. If properly plated with either platinum or palladium black, both should come to equilibrium within a few seconds of each other and