12
ASALYTICAL E D I T I O S
is no better than the thermometer that is used with it. I n general, a good mercury thermometer is better than a resistance couple, and a solid stem properly made and Calibrated is better than a Beckman. These statements are made deliberately. However, a certificate may be worth little if made on a thermometer of unseasoned glass, and, it may be added, is entirely worthless unless the corrections are ob-
Vol. 2,
KO.
1
served. Let it be noted also that thermometric accuracy as to actual temperatures is not essential, but the differential error over any range likely to occur in use should not exceed 0.03" F. (0.016" C.). By plotting the certificate variations in the form of a curve it is a simple matter to correct for the error involved in any reading. This refinement should be consistently observed.
Barium Oxide as a Desiccant' Harold S i m m o n s B o o t h and Lucille H. M c I n t y r e MORLEYCHRMICAL LABORATORY, WESTERNRESERVEUNIVERSITY.CLEVELAND, OHIO
H
ITHERTO experimenters in the field of gases have
been limited to the use of phosphorus pentoxide in order to obtain the greatest drying efficiency. It is needless to remind those who have worked with this substance of its many disadvantages, such as its striking tendency to take up water while the drying tube is being filled and to become sticky. When the opportunity2 to obtain a large quantity of unusually pure, porous, and absorptive barium oxide was presented it seemed worth while to make a study of the desiccating power of this substance, with a view to substituting barium oxide for phosphorus pentoxide wherever possible. Ten characteristics of a good desiccant are (IO): (1) High activitv. (2j Layge capacfty. (3) It must show little change in efficiency with rise in temperature. (4) It can be easily and repeatedly reactivated. ( 5 ) It will not become sticky on handling. (6) It will not form channels through use. (7) It will contract in volume on absorbing moisture (8) It will be neutral and form no reactive compounds which will act on the substance being dried. (9) It can be obtained cheaply and in large quantities (10) It will meet the requirements for the specific purpose t o which it is put in the laboratory.
volume on hydration is not a drawback if the material is correctly handled. The oxide cannot be reactivated, but its low cost makes this procedure unnecessary for most purposes. The barium oxide supplied was made by the reduction of barium carbonate with carbon and it is much more porous, absorptive, and reactive than the fused oxide obtained by the electric furnace process, and much purer. The barium oxide made in the electric furnace contains carbides which give acetylene on contact with moisture and render electric furnace barium oxide unfit for a desiccant. The barium oxide s u p plied is made a t such a low temperature that it contains no carbides and gives off no gases on treatment with water. A very pure barium oxide is said to be obtained by heating barium iodate gently in a crucible, but this is too expensive for general use. History
According to Baxter and Starkweather ( I ) , 1 liter of a gas dried over concentrated sulfuric acid retains 0.003 mg. of moisture. These investigators agree very well with Morley (6),who found that 0.25 mg. of moisture in 100 liters of air is left unabsorbed by sulfuric acid. Willard and Smith (1),working with anhydrous magnesium perchlorate, found that the amount of moisture left after Barium oxide has not, to our knowledge, been used, prior passing 210 liters of air through magnesium perchlorate a t to this study, for this purpose, but it seems t o meet most of 25" C. was unweighable, and that it took up nearly 60 per these requirements. It is very active, taking up moisture cent of its own weight of moisture. They also found that a t with great rapidity, with the evolution of considerable heat, 0" C. and for rates of flow up to 5 liters magnesium perchlorate forming barium hydroxide which is stable a t least up to trihydrate is as efficient as the anhydrous salt, but at higher 1000° C. and has no measurable vapor pressure a t room rates of flow the efficiency, though still high, falls off rapidly. Table I sums up the work of various authors on a number of temperatures. Further addition of water gives a series of hydrates, Ba (OH)2.H20, Ba(0H) *.3H20, Ba (OH)2.8H20, other drying agents. Ba(OH)2.16Hz0. The octahydrate in vacuum or in dry air T a b l e I--Absorption of M o i s t u r e R e p o r t e d i n L i t e r a t u r e a loses seven-eighths of its moisture and forms the monohydrate. RESIDUAL MOISTUREI N 1 LITERO F AIR A T 25' c. SUBSTANCE Unless sealed in a n air-tight container, barium oxide slowly IMP unites with the moisture in the air, forming the hydroxide, 1.40 Cupric sulfate (3) which, in turn, combines with the carbon dioxide in the air, 1.10 Zinc bromide ( 2 ) 0.80 Zinc chloride ( 2 ) and the final product of air-slaked oxide is barium carbonate. 0.36 Calcium chloride ( 2 ) 0.20 Calcium bromide ( 2 ) Barium oxide is obtainable in porous lumps or granules in 0.20 Calcium oxide ( I ) steel drums at a reasonable price. The material supplied to 0.16 Sodium hydroxide (4) 0.15 Boric acid anhydride (10) us has the following average composition, according to 0.00s Magnesium oxide (3) 0,007 Potassium hydroxide a t 50' C. (1) Rentschler: 99.6-99.7 per cent of BaO and traces of BaS04, 0,002 Potassium hvdroxide (1) Bas, BaC03, and Fe, Ca, and Sr. On hydration, it forms a Aluminum hkdroxide (3) 0.003 granular powder, which will not pack or form channels if the a Italic numbers in parentheses refer to Literature Cited. tube containing it is properly filled. The slight increase in LIorley's classic (6) on the absorption of moisture by phos1 Received August 26, 1929 Presented before t h e Division of Physiphoric anhydride shows that a t a current rate of 2 liters per cal and Inorganic Chemistry a t t h e 77th Meeting of t h e American Chemical Society, Columbus, Ohio, April 29 t o M a y 3, 1929. Presented by Lucllle hour air passed through 25 cc. of the substance contains less K McIntyre in partial fulfilment of t h e requirements for t h e degree of than 1mg. of water vapor in 40,000 liters. master of arts a t Western Reserve University, 1927. From the foregoing data, phosphoric anhydride, magnesium Through t h e kindness of M. J. Rentschler of t h e J. H. R . Products perchlorate, potassium hydroxide, and aluminum trioxide Co., Willoughby, Ohio.
January 15, 1930
I X D U S T R I A L AiYD ESGIAVEERI.XG CHEMISTRY
stand out as the most efficient drying agents. Magnesium perchlorate and aluminum trioxide may be reactivated easily, but phosphoric anhydride forms m-phosphoric acid and cannot be reclaimed readily. Apparatus
13
Typical Determination
All the materials used were chemically pure and all the usual precautions in handling such a gas apparatus were taken. The phosphorus pentoxide in both guard tubes, as well as in the preliminary drying tubes, was freed from phosphorus trioxide by ozonizing for several hours with a Siemens ozonizer, using dry air ( 5 ) . The ozone was then washed out by dry air. Phosphorus pentoxide was filled into the tubes in layers of about 3 em. in length between thin layers of glass wool to prevent channeling. Tube H was filled with selected granulated barium oxide in the same manner. After being filled, this tube was thoroughly shaken so that the particles of barium oxide became entangled in the fibers of the glass
The method adopted for testing the desiccating power of barium oxide consisted in partially saturating a definite amount of gas with a weighed amount of moisture from the saturation tube G (Figure 1) and drying the gas with barium oxide in tube H , using a guard tube, I , of phosphoric anhydride to retain any moisture that might escape the barium oxide. The tubes G, H , and I containing these three substances were connected by flat joints, permitting easy separation (8). They were weighed before and after the run to check the amount of moisture absorbed by the barium oxide against that lost by the saturation tube in saturating the gas. An adjustable manometer, E , on which the gas pressure could be read directly, was used to bring the gas in the system to the same pressure before and after each determination. When calculating the pressure, the temperature was taken into account each time, so that no error should arise from a possible change in the volume of the tubes before and after a run. An accurate gas meter, K , was chosen as the most practical means of recording the rate of gas flow. Sulfuric acid bubblers were used as a simple means of indicating the flow of gas a t a constant rate. At first, air was the gas used, and preliminary drying tubes, D , consisting of a calcium chloride tube, then a potassium hydroxide tube to remove carbon dioxide, and lastly two phosphoric anhydride Figure 1-Apparatus for Testing Desiccating Power of B a r i u m Oxide tubes, were used to dry the air, so that the absolute amount of moisture taken up by the barium wool. Thus the particles mere held in the meshes of the glass oxide would come from the saturation tube. Later, very pure wool, even after the oxide had broken down to the fine powder nitrogen was the gas used, as it was thought that the oxygen of the hydroxide, and channeling was thus prevented. in the air might combine with the barium oxide and so present Distilled water, freed from dissolved gases by boiling, was a source of error. A tank of especially pure oxygen-free drawn into tube G to such a height that a small extra pressure nitrogen, furnished by the General Electric Company, was of gas would not tend to force drops of water into the capillary attached to the apparatus by a seal of deKhotinsky cement. and so spoil the run. It was not necessary to use li-tubes as containers for the The moist capillary through which the water had entered water saturation, for barium oxide, and for phosphoric the tube was then carefully dried with a new pipe cleaner. anhydride, as the apparatus was not suspended in a water The tube was attached to the flat joint a t the coil F ( H , I , and bath. The reaction in this case was a chemical one and not J not attached) and dry nitrogen was run through the bythe formation of a hydrate; hence there was no vapor pres- pass until the capillary was dry. Xtrogen was then run sure to be taken into account. The conical joint in the end of through the water until the air had been replaced by nitrothe barium oxide tube, H , made it easy to reload. The gen. The last stopcock on the saturation tube and the first saturation tube, G, was designed so that dry air could be one of the manometer were closed and the reservoir of passed around it to dry the capillary between stopcocks and the tube brought to a predetermined pressure of approxiflat joints or to replace the air in the tubes with nitrogen after mately 1 atmosphere, and the other stopcock on the water reloading. A tubular water reservoir kept the gas bubbles tube was closed. The flat joints of tubes H and Z were small, so that they were more quickly saturated. Only a greased with a rubber grease of negligible vapor pressure and small reservoir was possible, because the whole tube had to be then clamped in place with flat-joint clamps as shown in short enough t o hang in the balance. Figure 1. Kitrogen was run through the whole apparatus, The glass coil, F , following the manometer, gave the neces- by-passing tube G for about 30 minutes to replace the air in sary elasticity to the whole system, thus taking the strain from the tubes. Then the first stopcock on the manometer and the the delicate parts of the apparatus. The mercury trap, B, last stopcock on tube I were closed and the system brought to placed immediately after the nitrogen tank, contained just the same predetermined pressure as that in tube G. enough mercury to allow gas to flow a t the necessary pressure. Stopcocks were closed, clamps were removed, and the grease Should the pressure become too great, the excess gas would was wiped from the flat joints with a clean cloth moistened escape through the mercury rather than through the rest of with carbon tetrachloride. A new pipe cleaner, dampened the system. with carbon tetrachloride, was used to remove any grease
L
14
ANALYTIC B L EDI TIOS
which had entered the capillaries of the flat joints. Tubes G, H , and I were carefully wiped with a moist lintless cloth and
1-01. 2, Yo. 1
impurity in the barium oxide and changed to nitrogen but without avail. Following this line of thought, runs 4 and 5 then wiped dry. Before hanging i n the balance case, each (Table 11) were made with ozonized barium oxide but with tube was scrutinized with a hand lens for fibers, grease, or more divergent results. The barium oxide in run 4 lost 5 mg., films of any sort. They were then hung in the balance case probably adsorbed ozone. on a wire stretched across the top. Counterpoises of the TThile the hydrolysis of barium sulfide and phosphide would same glass and similarly constructed, so as to have the same entail a loss in weight of the barium oxide tube, hydrolysis of surface area and displacement, were treated in the same way the carbide, nitride, and silicide would add to the weight. and hung next to their respective tubes. These counterpoises Accordingly, about 200 grams of the barium oxide were placed were heavier than the corresponding tubes, in order that the in a flask fitted with a delivery tube, a separatory funnel, and weights might be placed on the same side of the balance as a tube, running to the bottom of the flask, for admitting pure the tubes to avoid possible errors due to inequality of the nitrogen. After a slow current of nitrogen had swept all the length of the beam. Tubes were allowed to come to equi- air out of the flask, water was added through the separatory librium overnight before being weighed. funnel and steam was evolved by the heat of the reaction and was swept out by the nitrogen. The steam evolved was Table 11-Absorption of Water by Barium Oxide odorless, but nevertheless was bubbled into an ammoniacal GAS GAININ LOSS IN DIFFER- GAIXIX H20 NOT RUN USED TIMEBaO TCBEH20 TUBE ENCE P ? O ~ T U BABSORBED E solution of cuprous chloride. Acetylene was found to be Liters Hours Grams Grams Gram Gram Per c e n t absent. BARIUM OXIDE The purity of the steam from the reaction of water with the 380 2 1891 2,1888 1 101 - 0 . 0 0 0 3 0,0000 0.00 387 2.1222 2.1219 2 100 - 0 . 0 0 0 3 0,0000 0.00 barium oxide proved the purity of the barium oxide. We 2.3081 2.3060 3 103 485 -0.0021 0,0000 0.00 next checked the dates of the weighings with the humidities OZOIIZED BARIUM OXIDE 4 102 238 1.8484 1.8536 +0.0050 0.0002 0.01 reported by the Weather Bureau, and in so doing believe we 5 104 515 1.8792 1.8781 -0.0011 0.0000 0.00 discovered the cause of the divergences. We noted that the PARTIALLY AIR-SLAKED BARIUM OXIDE longer the period that elapsed between the time of making the 325 1.6497 1.6648 6 79 + 0 . 0 0 2 5 0,0176 1.07 237 7 129 2.9006 2 9069 + 0 . 0 0 6 1 0.0124 0.43 weighings and the assembly of the apparatus again for the 481 2.1822 2,1906 8 103 +0.0039 0.0123 0.56 experiment, the greater the divergence. Whereas usually not The weighing was carried out on a Ruprecht balance by the more than a day elapsed, in run 3 the elapsed time was over a method of deflections in a constant temperature room. The week. This gave time for moisture and carbon dioxide to tubes were then replaced in the system and dry nitrogen was enter the capillaries between the flat joints and the stopcocks, run through them by way of the by-pass until all the air Tvas and to be absorbed later by the barium oxide. Fortunately, replaced by nitrogen, a t a rate of 2 to 3 liters a n hour. Y h e n the distance between the adjacent stopcocks of H and I all the air had been driven out of the capillaries, the meter (Figure 1) was extremely short, and so the gain in weight of reading, time, and temperature were recorded and the nitrogen the P205 tube was inappreciable. On the other hand, the mas passed through the system through the tube G until capillaries connecting F with G and G with H were considerabout 100 liters had been used. At the conclusion of the run ably longer and thus the amount of moisture that could be dry nitrogen was again bypassed around the saturation tube gained by the barium oxide tube was just weighable. mhen so that all the moisture which may have been adsorbed in the explained, this divergence is a matter of no consequence as capillary between G and H was driven over into the barium far as the desiccating power of barium oxide is concerned. The results on runs 6, 7 , and 8 show that fresh barium oxide oxide tube. This required 4l/* hours. Then the system was again brought to the predetermined pressure as previously which is in no wise carbonated (air-slaked) should be used. described. The tubes were removed, cleaned with distilled Partial hydration does not interfere with absorption because water, and hung in the balance case as before. The counter- the hydrate takes up more water, forming a series of hydrates which then loses water to the adjacent fresh oxide which poises received the same treatment as before. fixes it firmly. Results In a number of other studies with gases being carried on in During the absorption of moisture the barium oxide this laboratory barium oxide is being used most successfully to changed from a coarsely granular mass to a coarsely porvdered replace phosphorus pentoxide as a drying agent. Its freedom substance, beginning a t the inlet end of the tube. The color from stickiness and ease of handling quickly made it a favorite changed a t the same time from a white to a yellowish pink, with the workers here. It should not be handled with moist probably due to traces of iron. This color change makes a n or wet hands, because the heat of reaction with the water may excellent indicator of the exhaustion of the ahsorbent. Be- be enough to cause a burn. It can be handled with dry ginning with run 2 , dry nitrogen was used in place of dry air. hands safely enough. As expansion occurs upon hydration, A preliminary series of runs (results not given) were made it should be mixed with glass wool or else left in lumps about to acquire the technic of the method. Then a series of three 7 to 10 mm. in diameter to prevent choking of the tube. I n general, on account of the coarse grain size of the barium determinations was made with great care (runs 1, 2 , and 3, Table 11). The calculations of the weighings were made to oxide as compared with phosphorus pentoxide, the drying the fifth place and the results rounded off, giving precision to tubes should be much larger and longer than those commonly the fourth place. Obviously in none of the results on runs 1, used with phosphorus pentoxide or else the gas rate should be 2, and 3 was the gain in the P205 tube more than 0.00004 much lower. When we do not wish to use as large a drying gram, and the average was less than 0.00003 gram, corre- tube as suggested, we sometimes use a pair of tubes, the first sponding roughly to 0.001 per cent of the water not absorbed. one containing BaO and the final one PzOj. Most of the That is, barium oxide will let pass about 1 mg. of moisture in water will be absorbed by the BaO, but we may run the BaO 10,000 liters of gas. The probability is that actually no to exhaustion because the P20swill protect it. This practice water vapor escapes through a properly made tube of barium enables us to use a dozen BaO tubes to one PzOstube and thus oxide. decreases the annoyance of filling the P20j tube frequently. We were a t a loss to explain the fact that the barium oxide The molecular weights of PzOj and BaO are 142 and 153, tube always gained slightly more than the amount of water respectively, and since each absorbs one molecule of water per volatilized. We thought it might be due to oxidation of some molecule, their final desiccating efficiencies are about the same.
ISDUSTRIAL AND ESGINEERILY'GCHE2VISTRY
January 15, 1930
Furthermore, the Ba(OH)2 formed can take up one more molecule of water, giving Ba(OH)?.H20, which is fairly stable a t room temperature. Whereas P206is all too readily reduced, yielding the volatile trioxide, Ba(OH)2requires very high temperatures for reduction. We have found BaO especially valuable for drying such basic gases as ammonia, for which it is far superior to metallic sodium, as it yields no gas in its desiccating action. Obviously, it should not be used for drying acidic gases or gases such as SiF4,which readily hydrolyze to give acids. Use of Barium Oxide in Desiccators
A preliminary study of the use of porous barium oxide in desiccators for analytical work has shown that the rate a t which it removes moisture from the desiccator is the same as that of phosphorus pentoxide, and that it is far superior, not only in this respect, but in many others to either calcium chloride or sulfuric acid. We have therefore adopted it in place of other desiccants in the course in quantitative analysis. It is much cheaper than the calcium chloride sold for desiccators and is conveniently obtainable from the manufacturer in steel drums. Barium Oxide as a Desiccant at High Temperatures
Preliminary studies have shown that the desiccating power of barium oxide is undiminished up to high temperatures. This would be expected in view of the fact that barium hydroxide is said to be stable up to 1000" C. and probably to higher temperatures. Summary
The results of this study show that the porous barium oxide made by the low temperature reduction of barium carbonate
15
by carbon fulfils the requirements for a good desiccant. Barium oxide made by this method has a high activity and large capacity, though the oxide cannot be reactivated. Being in a solid, porous form it is easily handled, does not become sticky, and does not channel if the container is properly filled, but, on the contrary, may choke up the tube unless room for expansion is left. On account of its granular nature, as compared to the fine particles of phosphorus pentoxide, barium oxide calls for larger drying tubes to accomplish the same drying rate, but the total efficiency is about the same or slightly better than for phosphorus pentoxide. Barium oxide should be kept in sealed containers out of contact with air containing carbon dioxide and moisture. Air-slaked (carbonated) barium oxide should not be used as a desiccant, as it is then only a part'ial absorbent and its speed of absorption is low. The absorption of moisture by fresh barium oxide is complete and permits its use in accurate gas research. Barium oxide prepared by low-temperature reduct'ion of the carbonate by carbon yields no gaseous products on reaction with water. Its desiccating action remains undiminished up to 1000" C. Its use in desiccators for analytical work and for general desiccating purposes is strongly recommended. Literature Cited (1) (2) (3) (4) (5) (6)
(7) (8) (9) (10)
Baxter and Starkweather, J . A m . Chcm. Soc., 33, 2038 (1918). Baxter and Warren. I b i d . , 33, 340 (1911). Dover and Marden, I b i d . . 39, 1609 (1917). McPherson, I b i d . , 39, 1317 (1917). Man!ey, J . Chem. SOC.,121, 331 (1922). Morley, J . A m . Chem. Soc., 26, 1171 (1904);A m . J. Sci., 34, 147 (1887). Willard and Smith, J . A m . Chem. Soc.. 44, 2255 (1922). Wourtzel, J . chim. p h w . , 11, 57 (1913). Walton and Rosenblum, J . A m . Chem. So,:., 60, 1618 (1928). Y o e , Chem. S e m s , 130, 340 (1925).
Rapid Determination of Nitrogen Peroxide in Nitrogen Peroxide-Air Mixtures' Colin W. Whittaker, F. 0. Lundstrom, and Albert R. Merz FERTILIZER A N D FIXEDN I T R O C E X
IXVESTIG.4TIOsS.
active nature of the nitrogen peroxide and particularly on account of the disturbing effect of the X2O4-2S02 equilibrium upon volume measurements a t ordinary temperatures. These difficulties can be overcome, however, by a proper choice of apparatus, materials, and conditions. This paper describes such an apparatus and a method whereby the concentration of the nitrogen peroxide can be rapidly and accurately determined without resorting to weighing or titration. General Considerations
Xitrogen peroxide reacts with or is soluble in the liquids usually employed for confining gases. It attacks mercury rapidly, combines with water and various salt solutions, and reacts with most oils and organic liquids or dissolves in them. Oils with low vapor pressures usually have high viscosities a t room temperature and are handled only with difficulty in a buret. For reasons to be discussed, the gas samples in 1
Received d u g u s t 7, 1929.
BUREAUO F
C H E X I S T R Y A S D SOILS, w A S H I S G t O N ,
D.
c.
very mobile, is not rapidly attacked by nitrogen peroxide, and has a vapor pressure low enough for use as a confining liquid. The disturbing effect of the equilibrium NnOa
* 2N02
(1)
may be avoided by measuring the volume of the gas mixture a t a temperature where the S20ris almost completely dissociated. At higher temperatures the reaction 2x02
* 2NO +
0 2
(2)
takes place and this reaction would be nearly as disturbing to volume measurements as (1). Inspection of data and curves for these equilibria showed that betm-een 150" and 160" C., a t moderate pressures, practically all the S204is decomposed into S O 2 and that the further decomposition of the N O z into S O and 0, has not yet become appreciable. Thus at these temperatures the percentage of X02 in nitrogen peroxide-air mixtures can be determined immediately, without computing
