INDUSTRIAL A N D ENGINEERING CHEMIXTRY
February, 1925
per cent as the average loss in weight due to drying. The weighings were made at intervals up to 140hours after drying. The graph, however, shows the results up to 50 hours during 6 5
183
which time the maximum gain was noted in the open dishes. The covered dishes in the desiccator continued to gain very slowly in weight throughout the experiment. Table IV gives the results of the fourth experiment. The outstanding feature of this experiment is the marked inefficiency of the calcium chloride desiccator.
6.0
2
? 2a
Table IV-Per 6.0
Time interval after drying Hours
4.5
P
I
E 1 .I
u
u1
4.0 G A I N l N ' W 8 I G H J O F ORJED N O U R U N D f R
9.5
P F F E R E M T CONDtI/ONS
3.0 2.3 2.0
Q
k
cent Molrture in Flour after;Coollng
5.5
1.5
1.0
0.3
..
o
5
IO
'5
20
TIME
25 30 IN H O U R S
35
40
45
50
Figure 6
91 140 5
7 - I N DESICCATORCovers on Covers off
(1) 13.33 13.33 13.33 13.33 13.30 13.29 13.29 13.29 l a . 29 13.23 13.19 13.15 13.14 13.06 13.00 12.83
(2) 13.35 13.35 13.35 13.35 13.32 13.31 13.31 13.32 13.32 13.28 13.25 13.20 13.19 13.14 13.09 12.96
(1) 13.20" 12.67 12.10 11.68 11.38 11.04 10.67 10.34 10.04 8.63 8.42 8.34 8.26 8.26 8.41 8.35
(2) 13.25' 12.62 12.10 11.07 11.30 11.00 10.65 10.34 10.06 8.80 8.60 8.54 8.45 8.45 8.63 8.49
Exposed to atmosphere with covers off (1) (2)
12.72 12.21 11.80 11.42 11.02 10.67 10.39 10.08 9.80 7.60 6.36 6.25 5.40
5.52 7.01 6.35
12.51 11.91 11.42 10.99 10.57 10.20 9.92 9.56 9.32 7.30 6.23 6.04 5.27 5.34 0.89 6.15
Cooled with covers tightly inserted into the dishes.
Production of Pure Hydrogen for Liquefaction'" By C. W. Kanolt and J. W. Cook BUREAU OF STANDARDS, WASHINGTON, D. C.
HE principle of the hydrogen liquefier is relatively
hydrogen was accumulated to permit the production of a simple, and several workersShave described liquefiers in useful quantity of liquid. detail. When very pure hydrogen is employed, probThe purification of gaseous hydrogen by liquid hydrogen is ably any of these liquefiers will produce liquid hydrogen m t h ill adapted for use in laboratories where liquid hydrogen is little difficulty, though not all with the same thermal effi- to be produced only in rather small quantities and at infrequent intervals; and if hydrogen of ciency. When the hydrogen is not The greatest difficulty in the liquefaction sufficient purity can be obtained extremely pure the expansion valve of hydrogen arises from the presence in the readily without using this method it is likely to become clogged a t once is desirable in any case. The purhydrogen of impurities, especially nitrogen when its temperature approaches and oxygen, which solidify in the hydrogen pose of the present paper is to dethat of liquid hydrogen; otherwise, investigascribe the production of hydrogen if the impurity is only slight, it may expansion valve and clog it. tion has been made of the of conof very high purity, using only be possible to obtain a few hundred tamination of hydrogen in its generation by simple means of purification. Such cubic centimeters of liquid before the clogging is complete. electrolysis, its storage in gas holders and a method theproducIf more than a very small quancylinders, and its compression. M~~~~ tion Of liquid hydrogen in laborahave been found for the convenient protories in which it has not yet been tity of liquid is required the use Of very pure hydrogen is imduction, without troublesome purification, made* of hydrogen of high purity, suitable for The impurities most likely to perative. I n the laboratory of liquefaction. The nitrogen content has cause clogging are nitrogen and Kamerlingh Onnes hydrogen is been reduced to o . ~ 1 ~ - ~ . 0 per 1 2 cent. oxygen. Oxygen in the hydrogen purified by cooling it with liquid hydrogen and so solidifyingimpuriThe method of analysis is described, is easily removed by causing it to ties.4 This method is regularly combine with hydrogen by the aid of heat or a catalytic agent. The employed in that laboratory in the production of considerable quantities of liquid hydrogen removal of nitrogen is less conveniently accomplished. The and has been found to give satisfaction. Before it could be writers have, however, produced hydrogen by electrolysis employed it was of course necessary to obtain liquid hydrogen and have prevented to a sufficient extent contamination by without its use. This was accomplished by running impure nitrogen so that no purification to remove nitrogen is necessary. Materials that are readily condensed a t the temperature of hydrogen into the liquefier until it clogged, and saving the hydrogen that passed through after the liquefier had become liquid air, including water vapor, carbon dioxide, and the cold enough to solidify impurities and before clogging was vapor of lubricating oil, are frozen in the heat interchanger complete. This hydrogen was pure, and by repeating the where the hydrogen is first cooled, and since there is here operation a considerable number of times sufficient pure more surface upon which they can condense, they are not likely to cause trouble. Drying the hydrogen with calcium 1 Received July 31, 1924. 2 Published by permission of the Director, U. S. Bureau of Standards. chloride is sufficient to permit the production of many liters a A list of journal references on the liquefaction of hydrogen, together of liquid hydrogen without the liquefier becoming clogged with a brief account of the method, will be found in a paper by Kanolt, with ice, even though calcium chloride is not a perfect drying J . Oplical SOC.A m . , 9,411 (1924). agent. 4 Kamerlingh Onnes, Leiden Communications No. 109b (1909).
T
184
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Hydrogen may contain sufficient nitrogen to produce clogging and yet contain so little that it cannot be detected by ordinary methods of gas analysis, which are accurate to perhaps 0.1 per cent when very carefully employed. This made it difficult to investigate sources of slight contamination with air. The difficulty was overcome by the development of a sensitive method of determining the percentage of nitrogen in hydrogen. Production of Hydrogen The hydrogen employed is generated electrolytically in a small generator having cells 17.8 em. (7 inches) square and generating only about 0.3 cubic meter of hydrogen per hour. A solution of potassium hydroxide is used in it. The current to the generator passes through an automatic circuit breaker of the polarized relay type, designed to break the circuit in case the polarity of the current should be accidentally reversed at the power house. Such an occurrence would, of course, result in the delivery of oxygen into the hydrogen holder and hydrogen into the oxygen holder, with danger of an explosion. After the generator is started it is allowed to operate for 2 or 3 hours before any of the hydrogen produced is delivered into the holder used for pure hydrogen. It is then usually operated continuously for several days and nights producing a large quantity of hydrogen, which is stored in cylinders. During the operation of the generator it is, of course, necessary to add water occasionally to replace that decomposed by electrolysis. In doing this, care is taken to avoid the introduction of air bubbles.
Vol. 17, KO.2
a direct determination of the oxygen content of the purified hydrogen was of interest. Since the amount of oxygen is far too small to be found by ordinary methods of analysis, a special method employing liquid hydrogen was used to freeze out and collect the impurity from a large quantity of hydrogen gas. Hydrogen from the generphor was passed successively through the platinum wire heater, a glass condenser cooled with ice t o remove the greater part of the water, a U tube immersed in liquid air to remove the remainder of the water and possibly other impurity, a U tube that could be immersed a t the proper time in liquid hydrogen to freeze out oxygen and nitrogen, and finally through a gas meter. The U tube to be immersed in liquid hydrogen was provided with a stopcock a t each end. Both U tubes contained small plugs of cotton to prevent particles of ice or frozen oxygen from being carried through mechanically. After a large quantity of hydrogen had passed through the apparatus the stopcocks were closed and the level of the liquid hydrogen was raised a little in order to cool thoroughly any material condensed at the top of the tube, where the temperature was not initially so low as that of liquid hydrogen. T o remove the greater part of the hydrogen in the tube it
Removal of Oxygen and Water
The oxygen contained in the hydrogen is removed by passing it over electrically heated platinum wires. The apparatus is shown in the figure, which includes a sectional view of the whole apparatus and a drawing upon a larger scale of the part that carries the platinum wires. The wires pass up and down at close intervals in the annular space between a central rod, A , and the surrounding iron pipe. The central location of the rod A is assured by the use of the spider R. The platinum wire is 0.2 mm. in diameter and has a total length of 140 em. It is strung over platinum hooks at C and D. These hooks are secured by clamping them at D between thick pieces of mica, which are carried on a movable part which can slide on the central rod. When the wire expands under the influence of heat this weight descends and keeps the wire taut. The current is carried to the platinum wire by heavy copper leads, which enter through a fiber disk, E , at the bottom. At F is a glass window clamped between fiber gaskets. It is preferable for the glass not to be too thick, since it is then more likely to leak as the result of unequal expansion of glass and metal. This window permits observation of the temperature of the wire, which is maintained a t a red heat. If there is any danger of a gas explosion it is well to make such observations with the aid of a mirror. When the gas generator is started the platinum wire is not heated until the impure gas, which a t first might be an explosive mixture, has been swept out of the apparatus. Instead of this apparatus one containing heated palladiumized or platinized asbestos might be used. These materials have the disadvantage that they are more likely to ignite an explosive mixture when the generator is started, even though they are not heated. The effectiveness of the hot platinum wire in causing combination of the oxygen is perhaps shown sufficiently by the lack of clogging in the hydrogen liquefier. However, since it seemed possible that some of the gas might pass through the spaces between the platinum wires without becoming sufficiently heated for complete combination of the oxygen,
Electric Heater for Removing Oxygen f r o m Hydrogen
was quickly evacuated to a pressure of about 5 mm. of mercury while still in the liquid hydrogen, and then allowed to warm to room temperature. Analyses of the impurities collected in this way were made by G. M. Shepherd. He removed the gas from the tube by means of a Topler pump, and determined the oxygen content by absorption in a pyrogallate solution contained in an apparatus of very small capacity designed to diminish the error arising from the solubility of gases in the water solution.
INDUSTEIAL A N D ENGINEERING CHEMISTRY
185
The writers have obtained satisfactory results with the use A preliminaT analysis on 28 litem of hydrogen indicakd the pmence of 0.00195 Fer cent of oxygen. A second analysis of oil in the holder, and the use of the more costly glycerol is a n 98 liters, which was more reliable because of the larger not a necessity, although it may be desirable when the quanquantity, indicated 0.0008 per cent of oxygen. This quantity tity required is not too large. is quite negligible. Compression of the Hydrogen The hydmgen is dried by means of calcium chloride after compression for liquefaction. When the gas is merely comAfter a gas holder full of pure hydrogen is prepared the pressed into cylinders for storage the drier is not used, but hydrogen is compressed into cylinders for storage. it is.introduced into the system when hydrogen is to be ' The compressor is a 4-stage, motor-driven Norwalk comliquefied. The drier used with a compressor of a displacement capacity of about 0.76 cubic meter per minute has an pressor, capable of producing a pressure of 200 atmospheres and having a displacement capacity of about 0.76 cubic inside diameter of 7.3 cm. and an inside length of 160 cm. meter per minute. Its actual rate of delivery is, of course, G a s H01der considerably lower than this, especially when used with hydrogen, which leaks back past valves and piston rings more The hydrogen from the generator, after passing the oxygen remover, is collected in a gas holder having a capacity of 2.25 rapidly than air. The motor is connected to the compressor cubic meters. The same or a similar holder is used €or the by a chain drive, thus avoiding the electric sparks that may hydrogen circulated through the liquefier during liquefaction. be produced by the friction of a belt. I n the compression of the hydrogen, either for storage or Following Kamerlingh Brines,$ the holder was first filled with machine oil. If water were used in the holder it would place in the operation of the liquefier, care must be taken to avoid a n unnecessary duty upon the drier, €or each time the dry contamination from two sources. All air must be removed hydrogen exhausted from the liquefier entered the holder it from the compressor and the connecting pipes; and no air would absorb water, which would have to be removed before must be sucked in through leaks, as the result of the partiaI the gas returned to the liquefier. The gas holder was con- vacuum produced a t the intake end of the compressor. The place in the compressor a t which air is most likely t o structed with a central stationary bell or false bottom within the movable bell, designed to diminish the amount of oil re- be sucked in is a t the stuffing box of the first-stage piston rod. quired, and incidentally to diminish the load on the floor of To avoid entrance of air a t this point a second stuffing box has been placed outside the first on the same piston rod. The the building. When hydrogen is stored over oil or water for any length annular space around the rod between the two stuffing of time it becomes slightly contaminated with nitrogen, which boxes is connected to the chamber containing hydrogen that dissolves in the liquid a t the surface exposed to the atmos- has undergone the first stage of compression. A leak a t the phere, is conveyed to the interior of the bell by diffusion or inner stuffing box can thus result only in the sucking in of by convection, and is there evolved into the hydrogen. this hydrogen, whereas a leak a t the outer box merely causes Oxygen may also enter, though when water is used in the a small loss of hydrogen. When the compressor is started, holder the oxygen may be absorbed b y the rusting of the iron and before the valve connecting its intake with the gas holder of the holder. When oil was used and the holder was allowed is opened, a vacuum pump is connected to the outlet and to remain nearly full of hydrogen, it was found by analysis operated until the pressure a t the outlet is reduced to about that the amount of nitrogen in the hydrogen increased by 1 cm. of mercury, the compressor being operated meanwhile. 0.011 per cent per day. The oil was light mineral machine During this evacuation a little hydrogen is admitted a t the oil having a density of 0.927 a t 60" F. and a Baybolt viscosity intake two or three times to sweep out residual air, especially of about 210 a t 100" F., which is equivalent to an absolute air in the compressor a t too low a pressure to lift poppet viscosity of about 0.48 c. g. s . units. If a heavier oil had been valves. It is best also to discard a little of the first hydrogen compressed after the compressor is started. used the diffusion might have been slower. It is known that the solubilities of nitrogen and some other Determination of Nitrogen in Hydrogen gases in glycerol are remarkably low.6 This suggested that glycerol used in a gas holder might permit the transfer of The efforts to locate and eliminate sources of contamination much less air than would oil or water. The high viscosity of of the hydrogen have been guided by determinations of the glycerol is also in its favor, since this would reduce convection amount of nitrogen contained in the hydrogen a t various and perhaps diffusion. Some rough experiments were made on a small scale on the stages of its handling. Such determinations are also used to rate of diffusion of nitrogen in various mixtures of pure check the purity of the hydrogen nom regularly produced for liquefaction. glycerol and water. With the rate in water as the unit, the The method employed is similar in principle to that rerate in 50 per cent glycerol was 0.2, that in 80 per cent it in various deglycerol was 0.04, and that in 98 per cent glycerol was 0.014. cently described by Dodge,7 but differs from tails. Both methods consist essentially of oxidizing the The rate found in these experiments for the kind of oil used in the holder was 1.4. These results are not accurate, but hydrogen to water by passing it over hot cupric oxide in an show plainly the utility of glycerol in this respect. Some apparatus previously well evacuated, removing water by crude glycerol was then placed in one of the gas holders. passing the residual gas through a cooled U tube, and calThis glycerol is quite impure and has a bad odor, which it culating the amount of nitrogen that remains from a measureimparts to the hydrogen stored in contact with it. This does ment of pressure made with a McLeod gage. A sample of about 200 cc. of hydrogen is collected in a no harm if the hydrogen is to be liquefied. It could, of course, be avoided by using distilled glycerol. The odor is not per- buret containing mercury. From this buret the hydrogen is ceptible in the room containing the holder. It was found that delivered very slowly through a 3-way stopcock to the in this holder the nitrogen content of the hydrogen increased analysis apparatus, which has been previously well evacuated. 0.0014 per cent per day. This is not so low as was expected By causing the mercury to rise and fall in the buret and manipulating the %way stopcock, the buret is used as a pisfrom experiments with pure glycerol, but is low enough. ton pump to cause the gas to circulate as many times as deLeiden Communications No. 94f (1906) sired through the circuit of the analysis apparatus, passing 8 Just, Z . physzk. Chem , 37, 342 (1931),Gniewasz and Walfisz, Ibtd 1, 70 (1887).
,
7
J . A m . Chem. Soc , 45, 1688 (1923).
186
INDUSThYAL A N D ENGINEERING CHEiMISTRY
successively over the heated cupric oxide, through the cooled U tube, and back to the buret. Usually it is passed around the circuit about four times. To diminish the danger of leaks the apparatus contains no stopcocks except the one by which hydrogen is introduced and the one on the buret. A barometric mercury valve is used to connect the apparatus with a McLeod gage and another connects both with the vacuum pump. Great care is taken to avoid the trapping of air between the mercury and the glass in the buret, the mercury valves, and the lower tube of the McLeod gage. This is avoided by keeping the glass and the mercury clean and by moving the mercury up and dbwn while the apparatus is being pumped out. About 25 grams of cupric oxide are used. It is contained in a Pyrex tube surrounded by a copper tube to equalize temperature, and is heated by a flame. Previous to an analysis the cupric oxide is heated for some time to about 500" C. in a good vacuum to drive off absorbed gases. The temperature is reduced to about 425' C. for analysis. Considerable variation from this temperature is probably permissible; however, there is an advantage in making the analysis with the cupric oxide a t a lower temperature than that to which it was heated during the evacuation of the apparatus. There will then be less gas evolved from the oxide during the analysis. When the cupric oxide has been partly reduced it is easily re-oxidized by heating it and drawing air through the apparatus. As a matter of precaution when accurate results are required, the re-oxidation is carried out before every analysis. This may not be necessary. The U tube in which water is separated is cooled with liquid air. Dodge used a freezing mixture for this purpose. To obtain the highest accuracy it has been found an advantage to carry out the condensation of water first with only the bottom of the U tube immersed in liquid air, and when this condensation is practically complete to raise the level of the liquid air nearly to the top of the U tube before measuring $he pressure. The reason for this is that, if the liquid air level is kept constant, ice will form in the upper part of the first branch of the tube a t a point where the temperature is not far below the freezing point, and this ice will evolve an amount of vapor sufficient to produce an error in the pressure measurement corresponding perhaps to several thousandths of a per cent of nitrogen. With the procedure recommended, the ice is formed a t a lower point in the tube, and when the level of the liquid air is raised the ice is all cooled to the temperature of liquid air. When duplicate analyses were made upon the same specimen of hydrogen, containing a few hundredths of 1per cent of nitrogen, the results agreed within 0.001 per cent. It is of interest to determine whether there is any systematic error in the results. The most important possible sources of error are probably the evolution of absorbed gas by the cupric oxide and failure to remove all hydrogen. Spectroscopic examination of the residual gas has revealed nothing but nitrogen and argon. I n order to check the method, analyses have been made of hydrogen of a high degree of purity, obtained by the evaporation of liquid hydrogen. To obtain the purest gaseous hydrogen from the liquid certain precautions are necessary. Liquid hydrogen is liable to contain particles of solid nitrogen and oxygen. There may be such particles adhering to the walls of the container above the level of the liquid and where the temperature is high enough to permit slow evaporation of the solids. Gaseous hydrogen drawn directly from the top of the container may be contaminated in this way. To avoid this an apparatus was employed in which filtered liquid hydrogen was evaporated with precautions to avoid the presence of air. An analysis of hydrogen obtained in this way indicated the
Vol. 17, No. 2
presence of 0.002 per cent of nitrogen. It is to be noted that practically all possible sources of error would give a high result. The writers have no certain evidence as to the source of this nitrogen. After the pressure of the residual nitrogen had been determined, the liquid air surrounding the U tube in which water is condensed was replaced by liquid hydrogen. The pressure quickly fell so low that it could not be measured with the McLeod gage, indicating that the gas not frozen out by the liquid hydrogen was less than 0.000002per cent gf the original sample. This indicates that the residue of 0.002 per cent was nitrogen and not hydrogen. The writers believe the method of analysis is a t least accurate to 0.002 per cent when the quantity of nitrogen is small. Purity of Compressed Hydrogen and Operation of Liquefier Many determinations have been made of the nitrogen content of hydrogen that has been compressed into cylinders for storage. The hydrogen now produced contains from 0.010 to 0.012 per cent of nitrogen. The oxygen content has not been determined, but since it has been shown that the amount of oxygen passing the platinum wire heater is negligible, and since oxygen cannot enter the hydrogen after it passes the heater except in company with nitrogen from the air, it is unlikely that the oxygen content is much more than onefourth of the nitrogen content. The writers' earlier experience, with hydrogen of higher nitrogen content, indicated that this content cannot be more than a few hundredths of 1 per cent without clogging; a t least, this is true of the liquefier employed. It is very possible that the expansion valves of the liquefiers used by some other workers have been better designed with regard to the avoidance of clogging. The hydrogen liquefier has been operated many times since this hydrogen was available and has never become clogged to such an extent that the obstruction could not be removed readily by manipulating the expansion valve. Such partial clogging as has occurred has happened more often in the earlier part of the period of liquefaction than later. Usually about 4 or 5 liters of liquid are produced at a time, a t the rate of about 2 liters per hour.
Discovery of Potash in Crane County, Texas The Department of the Interior announces the discovery of potash in a well on the Cowden ranch, in Crane County, Texas, about 50 miles southwest of Midland. Cuttings of the beds penetrated and samples of the water used in drilling were taken from the bailer a t intervals of 5 feet through the greater part of the well. The samples of cuttings analyzed by the Geological Survey were obtained from depths between 560 and 1765 feet. The best sample, which contained 7.40 per cent of potash (KzO), was taken from a depth between 1065 and 1070 feet. The interval between 1070 and 1075 feet yielded a sample containing 7.20 per cent of potash. Another sample, containing 7.16 per cent of potash, was obtained from a depth between 945 and 950 feet. Samples taken at 890 to 895 feet and a t 895 to 900 feet contained 6.24 and 5.10 per cent of potash, respectively. In addition, samples taken a t the depths given cantained potash in the quantities stated: 905 to 910 feet, 4.28 per cent; 1050 to 1055 feet, 2.75 per cent; 950 to 955 feet, 2.50 per cent; 700 to 705 feet, 1.62 per cent. No other sample contained as much as 1.50 per cent of potash. Analyses were also made of samples of drilling water, the quantity of dissolved salts in the samples ranging from 32 to 34.5 grams per 100 cc. The Cowden well shows the existence in this intermediate area of potash-bearing beds similar to those of the Santa Rita well, in Reagan County, on the east and to those of the River well and the Means well, in. Ward and Loving Counties, respectively, on the west. I n this well, however, the potash-bearing beds are 200 feet or more nearer the surface than in the other wells of the region thus far studied.
