A W , 1917
T H E J O U R N A L O F I N D U S T R I A L AlVD EATGIA7EERING C H E M I S T R Y
of t h e work done b y X-light, using a t u b e of unit dimension, P being t h e penetration as measured on a Wehnelt penetrometer. Using a slide rule covering t h e equation DZTZ
x
D
= >-
c PZ
P = Wehnelt penetrometer readings target and glass X = exposure in seconds T = thickness of glass C = current measured in milliamperes = distance in inches between
we have a formula based upon a hypothetical unit of light which one can vary t o produce with exactness a n y desired result. Each make of glass, of course, has its own rate of speed of change by which t h e r a l u e X must be multiplied. T H E O R Y OF O P E R A T I O N
The coloring of purple glass is undoubtedly due t o manganese, yet t h e color of this glass is not exactly t h e same as in t h e manganese specimens, which have been tested. This, of course, can possibly be accounted for in several ways, such as t h e difference in t h e chemical substance of t h e glasses, or due t o t h e oxidation of t h e manganese, which may be different as obtained b y radiant energy t h a n b y t h e regular glass manufacturing process. T h e other colors obtainable, very likely follow along t h e same lines, b u t i t is also hard t o believe t h a t anything else b u t a direct physical change in t h e material, or a direct molecular rearrangement has taken place. Considering t h a t b y t h e application of heat, molecules can be rearranged, t h e action would appear, if taken synthetically, more naturally physical t h a n chemical. S Z; M MA R P
I-White glass turns t o different colors under this method. 11-Knowing t h e composition of t h e white glass, t h e color can be predetermined. 111-The depth of coloring of t h e glass is dependent on penetration of t h e rays, h e w e controllable. IV-The action is molecular a n d not confined t o t h e surface of t h e glass and t h e color is in and through t h e glass itself. Y-The action is reversible. VI-In coloring glass by t h e above-described method, results can be obtained which are not possible with glass colored by chemicals. VII-Other analogous substances, such as porcelain, quartz, and some of t h e precious and semi-precious stones, particularly those colored by manganese, respond t o this method of treatment. . The writer of this article makes no pretense t o accurate scientific knowledge, b u t gives t h e results of his observations and methodical experiments with t h e well-known phenomenon in t h e hope t h a t they may add some mite t o t h e s u m of human knowledge and may stimulate those who are better versed in scientific studies t o ascertain t h e exact cause and operations of this interesting power of t h e short wave lengths of light. ROSENTAAL ELECTRICAL LABORATORY CAMDEN,
N E W JERSEY
737
THE CHEMICAL CONTROL OF AMMONIA OXIDATION By PAULJ. Fox Received June 21. 1917
I n t h e oxidation of ammonia t o produce nitrous or nitric acid, t h e ammonia, mixed with air, is passed over a catalyzer heated t o a red heat. The ammonia content t o t h e air-ammonia mixture is given either b y running t h e air through aqueous ammonia or by mixing t h e ammonia gas with air. When t h e ammonia content is obtained by passing t h e air through aqueous ammonia, t h e mixture, of course, is saturated with water vapor a t t h e given temperature. I n t h e operation of this process, either on a n experimental or manufacturing scale, one of t h e most pressing problems is t h e chemical control, for on i t depends t h e accurate adjustment of t h e factors necessary t o t h e efficiency of t h e plant. I n fact in starting a new commercial unit, or getting d a t a on a design of furnace, or merely in testing a new catalyzer, especially over any period of time, t h e principal practical issue is finding out exactly what t h e chemical performace is under the various conditions (temperature and character of catalyzer, speed and composition of ammonia-air mixture, etc.). The chemical control naturally falls into four parts: ( I ) t h e examination of t h e gas before passing to t h e catalyzer, and (Z:I after coming from t h e catalyzer, (3) t h e working up of t h e results, and (4) t h e determination of nitrous acid. For t h e determination of t h e fairly high content' of ammonia in t h e entering gas, t h e ordinary gas analysis methods with mercury as confining liquid are applicable or t h e ammonia may be absorbed in standard acid and titrated. -4 thorough discussion of t h e various absorbing arrangements will be found in a paper by Edwards2 on t h e absorption of ammonia in illuminating gas. The method by absorbing in standard acid has t h e advantage t h a t a much larger sample can be used-in fact a continuous sample can be taken-and t h a t no mercury is required. T o test t h e Cumming absorber, t h e writer ran 1000 cc,of I O per cent ammoniagas through one like t h a t figured by Edwards, another absorber being connected in series beyond it. S o t a trace of ammonia passed into t h e second absorber, showing t h a t one is sufficient t o collect all t h e ammonia. It has occurred t o t h e writer that with this type of absorber it is possible t o determine t h e ammonia without making any titration. This is done by putting in a measured quantity of standard acid, coloring with an indicator and bubbling through t h e ammoniaair mixture, until t h e color turns. If t h e gas has been collected in an aspirating bottle, t h e volume corresponding t o t h e quantity of standard acid used is known, a n d the per cent of ammonia in t h e original mixture can be easily computed. T h e reason why this is possible is t h a t in t h e Cumming absorber there is a fair circulation, and with a little practice i t is not difficult t o hit t h e turning point, as t h e liquid is always approximately of t h e same composition. At t h e same time, t h e appearance serves warning as t o when t h e change will occur. 1 T h e theoretical air-ammonia mixture (dry) contains 14.33 per cent of ammonia. 2 J. D. Edwards, Bureau of Standards, Technologic Paper, 34 (1914).
738
T H E J O U R N A L OF I N D C S T R I A L A N D EAVGINEERING C H E M I S T R Y
T h e writer fully agrees with t h e favorable opinion of Edwards on sodium alizarin sulfonate as an indicator for titration in t h e presence of ammonia. I t is especially useful for making t h e ammonia determination without titrating. Though circulation is fairly good in t h e Cumming apparatus figured by Edwards. t h e writer suggests a n altered form (Fig. I ) designed with - a view t o promote a more even circulation and avoid STOPPER dead spaces, especially for use when the ammonia is determined by measuring t h e volume of gas (in an aspirating bottle) necessary t o neutralize a measured quantity of standard acid. FIG I I n the figure. it will be noticed t h a t t h e injector is placed slightly t o t h e right of t h e mouth of t h e semi-circular lower p a r t , which is made of somewhat larger tubing t h a n t h e horizontal piece, having in view a rapid circulation, and reasonable capacity. The stopcock piece should be made of fine bore tubing with a minimum of dead space. T h e stopper may be of glass or rubber. I t is obvious t h a t a similar plan might be used for other gases, possibly even for carbon dioxide b y staining caustic soda with phenolphthalein, passing t h e gas t o decolorization, a n d using a measuring p u m p instead of a n aspirating bottle, if more convenient. T h e principal difficulty, however, is in t h e analysis of t h e exit gas, i. e . , t h e gas after leaving t h e catalyzer. T h e reaction may be considered as proceeding as follows: 4NH3 jOz = 4 N O 6Hz0 b u t there is commonly some excess of oxygen, so t h a t a t least a p a r t of t h e N O exists as NOz or N z 0 4 . Also, there may be uncombusted ammonia, as ammonium nitrite or nitrate present, and there is always, of course, water vapor and nitrogen. hlost of t h e literature on this subject refers only t o t h e examination of gases from arc processes, where there is no question of ammonia a n d where there is always a great excess of oxygen t o convert N O into NO*. As Nz04 is a n acidforming oxide, forming a mixture of nitrous and nitric acids with water, t h e standard method consists in absorbing t h e oxides in standard alkali a n d titrating t h e excess of alkali, either with or without t h e addition of hydrogen peroxide t o oxidize t h e nitrous t o nitric acid. These methods are fully described a n d tested in a paper b y Ehrlich and Russ.' The method b y t h e absorption in standard alkali, first taking a measured volume of gas, is not applicable t o t h e exit gas from ammonia oxidation since: ( I ) When a n a t t e m p t is made t o obtain a sample, a large condensation of water takes place from t h e hot gas, making it impossible t o get t h e true volume, t o say nothing of t h e p a r t of t h e nitrogen oxides dissolved in t h e water. Obviously t h e sample must be t a k e n before condensation begins. ( 2 ) There m a y not be sufficient oxygen present t o oxidize all t h e nitric oxide ( N O ) t o nitrogen dioxide
+
1
+
Ehrlich and Russ, Monatsh, 32 (1911). 917.
1-01. 9 , S o . 8
(NOz), and nitric oxide is only slightly absorbed b y water or alkali-water absorbs about j per cent of its volume a t I j o when t h e partial pressure of t h e nitric oxide above is 7 6 0 mm. ( 3 ) If hydrogen peroxide is added t o t h e alkali, it is not certain t h a t nitric acid is formed b y t h e interaction of t h e hydrogen peroxide and t h e nitric oxide, for Schoenbein has shown t h a t t h e acid liquid so formed causes potassium iodide paste t o t u r n blue, whence he concludes t h a t the compound formed is not nitric acid. A more serious objection is t h a t , as also has been shown b y Schoenbein, hydrogen peroxide abundantly oxidizes ammonia t o ammonium nitrite.' This oxidizing effect of hydrogen peroxide on ammonia renders the reagent inapplicable-if t h e condition is not provided for-to the determination of nitrogen oxides in t h e exit gas, since uncombusted ammonia would appear as oxidized nitrogen. Ozone would be an ideal oxidizer for t h e case since it oxidizes without change of volume if it were not for t h e fact t h a t it also oxidizes ammonia.* Ozone oxidizes nitrogen oxides, in t h e presence of moisture, t o nitric acid. On t h e other h a n d , t h e use of hydrogen peroxide or similar oxidizes is advantageous, in fact necessary if complete absorption is t o be obtained. This is because there is a decomposition of t h e nitrite ion in t h e sense of t h e following e q ~ a t i o n : ~ 2x02 =
NO
+ NO3
T h e oxidizing agent is necessary t o oxidize t h e nitrous acid t o nitric acid, and thus prevent t h e decomposition mentioned. Incidentally t o these questions, it must be remembered t h a t the volume of t h e sample taken, or some similar d a t u m , must be found in order t o make t h e efficiency calculation. This must be ascertained b y indirect means, as i t is impossible t o measure t h e volume directly on account of t h e abundant condensation of water, as previously mentioned. It has occurred t o the writer t h a t t h e difficulties could be overcome a n d a satisfactory determination made b y t h e following method: Aspirate t h e gas from t h e exit pipe, b u t before it reaches t h e absorption. apparatus, mix it with a sufficient (measured) volume of oxygen or air t o convert all t h e nitric oxide into nitrogen dioxide. I t will be shown presently how i t is possible t o do this with no graduated apparatus. This insures t h a t all t h e nitric oxide enters t h e absorption apparatus as nitrogen dioxide, without a n y of t h e ammonia being oxidized. Use t w o absorption tubes and in t h e first, place t h e standard alkali solution-say N / I O alkali-without anything else; in t h e Becond t u b e place a smaller quantity of standard alkali, together with hydrogen p e r ~ x i d e . ~By this means t h e ammonium nitrite stays in t h e first t u b e where there is no hydrogen peroxide t o oxidize it. It might be thought as a n objection t h a t as t h e solution in t h e first t u b e is alkaline, ammonia would be 1745; see also other 1 Schoenhein, Weith and Weber, Ber., 7 (1874), papers by Schoenbein in the J . puakt. Chem. 2 Ilosway de Ilosva, Ber., 27 (1894), 3500. 3 Abegg and Pick, Z . anorg. Chem.. 6 1 (1906). 1-28. 4 T h e hydrogen peroxide in the absorbing liquid should have a concentration of 1 per cent.
Aug., 1917
T H E J O L ’ R N A L OF I N D U S T R I A L A N D E LVGIN E E RI LVG C H E M I S I’R Y
set free, and carried over b y t h e slow (aspirated) air current into t h e tube containing t h e hydrogen peroxide. Perman.’ however, has aspirated air through aqueous ammonia solution of many different concendc trations and has plotted - against c (where c is t h e dt
concentration of ammonia in t h e solution a n d t t h e time obtaining the result t h a t a t lonr concentrations of a m monia. i$ i. e.. t h e amount of ammonia removed in dt ’ unit time, becomes very small. If his curve is prod 1: duced so t h a t -~ becomes zero, t h e concentration is dt
still much abox-e what would be obtained in t h e first absorption tube. In other words. a t t h e concentrations of ammonia in question no ammonia whatever is removed. The \Triter aspirated a current of air over night through a n ‘ammonia solution (about 8 per cent) and in t h e morning the solutions till smelled very strongly of ammonia. However, in case very large quantities of ammonia were passed, which would scarcely occur in practice, another t u b e could be inserted before reaching t h e hydrogen peroxide tube. I n t h e experimental test of t h e absorption, pure d r y nitric oxide was made in a nitrometer and portions measured off in a gas burette, over mercury. From t h e burette it was conducted b y glass tubing t o one leg of a Y-glass piece, through t h e other leg of which entered the air. I n each leg was a constriction t o throttle t h e entering gases and prevent back diffusion, either of t h e air into t h e burette containing t h e nitric oxide, or of t h e nitric oxide into t h e air reservoir, T h e mixed gases then proceed t o t h e absorption apparatus, of which t h e best form in t h e writer’s judgment is a tall modified Emmerling tower (Fig. 11) with a column of beads about five inches long.2 4 good many perti-
D
,-c
r: y h S S
rod supportinp beuds
sc, screw cock w, wash
boR/e
FIG. 11-APPARATUS POR AESORBING KITROUSGASES
nent details as t o t h e washing out and manipulation of this form of absorber m a y be found in t h e paper b y Edwards. Two of these are used for t h e reasons set forth above. I n t o t h e first was placed z j cc. of N / I O sodium hydroxide, and into t h e second, I O cc. of ,V ‘ I O sodium hydroxide and z j or I O cc. of ordinary J . Chem. Soc. (London), 67 (1895). 874. The rather exaggerated space for liquid below is to give the apparatus greater capacity. There is not much space for liquid around the beads. T h e beads should be above the clear liquid to remove the last traces. 1
739
3 per cent hydrogen peroxide.’ As only a small part goes over into t h e second absorber, i t may be advantageously smaller, if “perhydrol” is used as a source of hydrogen peroxide. T h e aspiration is effected b y a n air-tight aspirating bottle with a rubber t u b e outlet a t t h e bottom, running +into a lei-eling bottle. Xt t h e end of t h e run, after leveling. the amount of water which had escaped is equal t o t h e r-olume of air aspirated.2 So far as tests are concerned. it is of course not necessary t o use a n air or oxygen reseryoir a t all, since t h e total volume aspirated a n d t h e rolume of t h e nitric oxide are knon-n. I n a n actual test, however, the volume of air (or preferably oxygen) must be known in order t o make t h e necessary allowance for it in calculating the volume of t h e sample taken. Instead of having a graduated vessel for the oxygen, one whose total contents are know-like a sampling pipetteis more convenient. One end is open and immersed in water in a battery jar (with a suitable guide above), and from t h e other end t h e oxygen may be drawn under a n even pressure, t h e pipette filling u p with mater from b e l 0 ~ . 3 In case t h e reservoir is not e m p t y when the sample taking is completed, i t is only necessary t o continue t h e aspirating until t h e reservoir is e m p t y of oxygen, and subtract its total volume as will be discussed below. Or, if desired, t h e volume of water admitted may be measured. In t h e tests t h e air was drawn from a reservoir t o avoid possible oxides of nitrogen in the laboratory atmosphere. An alternative arrangement shown in t h e figure is equally convenient, and is better when air is used. ABSORPTION O F NITROGEN 1)IOXIDE = N/10 or N/5 or N/10 Expt. cc. Y / 5 soda cc. cc. found Recovery So. O‘, 760 mm. theory by titration 10.49 1.. . . . . . . . . . 23.5 10.61 101 10.00 2 . . . . . . . . . . 22.4 10.13 101 6.83 3 . . . . . . . . . 15.3 6 95 102 1i.05 4. . . . . . . . . . . 3 8 . 2 16 91 99 13.79 5 . . . . . . . . . . . 30.9 13 98 101 21 43 100.5 $ . , . . . . . . . . . 95.6 21.32 21.39 21 56 100.8 I . .......... 95.9 K O taken
h-0 in Mixture
70 i.6 9.2 11.1 9.1 12.2 11.2 11.5
As will be seen, t h e results, while very satisfactory, have a tendency t o be a little high (with t h e except h a n would be accounted for tion of No. 4)-higher b y titration errors. I n t h e case of No. 4, t h e gases were purposely passed faster t h a n would ordinarily be done, b u t even here t h e results are good. Ehrlich and Russ4 working, as mentioned, on a direct cornbination of nitrogen and oxygen process, a n d without t h e complications necessary in ammonia work, as previously discussed, also obtained slightly high results, even when using (apparently) only one absorber. Indeed, if t h e extreme of accuracy were necessary, i t would be possible t o use pure nitric oxide from a nitrometer as t h e ultimate standard. I t is advisable t o obtain a n “overall” correction for t h e whole apparatus, T h e alkali should be on top of the peroxide as much as possible. I n making the tests on absorption, this method of mixing pure nitric oxide and air is preferable t o diluting the nitric oxide in the burette, since the latter plan requires too large a space over mercury. Besides, any trace of oxygen in the diluting gas forms nitrogen dioxide, which attacks the mercury even if the gases have been bubbled through sulfuric acid. 3 4 ready improvisation of such a n arrangement is a separatory funnel. closed with a one hole stopper and inverted in a battery jar full of water. A wash bottle with leveling bottle attached is equally good, as in Fig. 11. 4 Loc. cit. 1
2
740
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
by adding t h e standard alkali a n d peroxide, aspirating about a liter of air through, a n d removing t h e alkali, washing the apparatus, a n d titrating. I n this way small errors in t h e measuring instruments, as well as t h e acidity of t h e peroxide, are taken up. This “overall” correction was used on Experiments 6 and 7 where much larger amounts of gas were handled t h a n in Experiments 1-5, in which only t h e peroxide correction was applied. T h e writer thought i t worth while t o see whether approximate results in t h e absence of ammonia and in spite of t h e objections mentioned might not be obtained b y attempting t o absorb nitric oxide mixed with air insufficient t o convert t h e nitric oxide into nitrogen dioxide, in alkaline hydrogen peroxide. This would avoid t h e necessity of previously mixing the sample with oxygen, putting t h e d u t y of oxidizing t h e nitric oxide wholly on the hydrogen peroxide. It was found, however, t h a t t h e nitric oxide bubbles freely through t h e alkaline peroxide, a n d turns into brown fumes on entering t h e air. Hydrogen peroxide instantly oxidizes nitrous acid, but only slowly a n d incompletely acts on nitric oxide, and possibly, as mentioned, not with t h e production of nitric acid. I n t h e making of an actual determination, t h e following practical details are worth mentioning: Set u p t h e apparatus as in Fig. 11. T h e sample is t a k e n through a capillary tube placed as close t o t h e catalyzer as possible without melting the glass.’ T h e reason for using a capillary is t h a t as soon as t h e exit gas cools, large quantities of water condense from it, and in a capillary this water is pushed along with t h e movement of gas. All this water must, of course, be included in t h e sample, b u t no water should be included t h a t has condensed before t h e taking of t h e sample begins. Hence the taking of t h e sample must commence before t h e dew point is reached, or the results will be worthless. The sample may be taken as slowly as desired t o average t h e determination over some time-a plan highly desirable when working with catalyzers. About a liter of gas should be used, a t least, t o avoid letting small constant errors have too great an effect on t h e result. Great care must be taken t o have tight connections throughout t h e apparatus-a condition not difficult t o secure if first class, rather soft, rubber stoppers a n d good rubber tubing are available. P u t 2 5 cc. N / 5 caustic soda in t h e absorber nearest t h e sampling capillary a n d 2 0 cc. with I O cc. of 3 per cent hydrogen peroxide in t h e other one. T h e wash bottle next t h e aspirating bottle saves t h e determination in case of a sudden violent passage of gas, a n d also indicates a n insufficiency of oxygen, as t h e space above t h e small quantity of water it should contain has sufficient air t o t u r n t h e passing gas brown if all the nitric oxide has not already been removed from it. Fill the bottle O2 with oxygen, taking care t h a t every bit of water is drained out,* elevate t h e leveling bottle about 2 feet a n d open SC 4, which puts the oxygen under a little pressure, SC 2 being, of course, closed. With SC I closed, p u t t h e outlet of t h e aspirating bot1The
glass might well be platinized, or a silica tube used. The water may be poured out as there is no special point in having pure oxygen. 3
Vol. 9 , No. 8
tle on a lower level, cautiously open SC I t o let slow bubbles pass, and a t t h e same time open SC 2 slightly t o admit oxygen. T h e amount t o admit depends on t h e strength of the exit gas as one volume of nitric oxide consumes one-half a volume of oxygen. But a much larger quantity of oxygen may be used, t h e rapidity of the bubbles serving as a guide, perhaps one bubble of oxygen t o three of exit gas-a quantity of oxygen sufficient for all possible conditions. If desired, a wash bottle may be placed after t h e oxygen bottle. When t h e taking of t h e sample has been concluded, close SC I a n d SC 2 , a n d t h e intake capillary, put t h e wash bottle near t h e aspirator over on its side, a n d level the contents of t h e aspirating bottle with its outlet bottle, finally opening SC I a n d SC 3 t o get t h e level exact.’ T h e volume of water in t h e outlet bottle is the quantity f. I t is clear t h a t it is of no importance whether t h e ‘volume f is taken a t t h e same temperature a n d pressure as t h a t a t which t h e entering ammonia-air mixture is analyzed or not, as the ammonia in t h e intake gas is expressed here as a ratio b. T h e quantity. f must, however, be measured a t t h e same temperature a n d pressure as the oxygen added. T o find t h e volume of oxygen added, either continue passing it until t h e oxygen container (of known volume) is filled with water, or level the bottle a n d measure t h e water t h a t has flowed in. I n a n y case some oxygen must be passed t o wash out the connections. Titrate t h e liquid from each burette separately. Two or three washings are sufficient t o remove t h e liquid from the beads if some adjustment has been made between t h e soda added a n d t h e nitrous gases present. If t h e liquid is acid, t h e determination is not necessarily lost. For a n indicator, sodium alizarin sulfonate is the best, as it is not affected b y moderate amounts of hydrogen peroxide or nitrous acid.* The gas is to be calculated t o nitric oxide ( N O ) a t the temperature and pressure a t which t h e oxygen excess and f (or t h e volume in the aspirator outlet) is measured. This calculation can be quickly made with sufficient accuracy on a slide rule, considering t h a t for this purTaking t h e gram pose nitric oxide is a perfect gas. molecular volume a t 2 2 4 1 2 , we see t h a t each cc. of N / 5 alkali (previously corrected by the “overall” correction already mentioned) is equivalent t o 4 , 4 8 2 CC. of nitric oxide a t o o and 760 mm. I n the sequel the volume for room temperature and pressure is referred t o as Vno. Hydrogen peroxide is rather easily decomposed a n d the author thought t h a t possibly enough oxygen might be carried over into the aspirator bottle t o affect the results. T o test this point, t w o portions of about a liter each of air were aspirated through t h e apparatus, a n d the hydrogen peroxide titrated with permanganate (ten cc. of peroxide, with 2 0 cc. of N / I O caustic soda). It was found t h a t t h e alkaline 1 SC 3 is the screw cock t o a water leveling gauge, as the diameter of the aspirating bottle might be too large to get an accurate level in the ordinary way. If oxygen 2 A n observation paralleling Schoenbein’s was made here. is deficient, a n d nitric oxide passes t o the hydrogen peroxide absorber, a compound is formed t h a t acts on the sodium alizarin sulfonate and causes irregularity. This is a sign of insufficient oxygen.
A%., 1917
T H E J O U R N A L OF I N D U S T R I A L A N D ENGIJEERING CHEMISTRY
I per cent peroxide yielded only in one case 6 . 0 cc. a n d in t h e other 6 . 6 cc. While this amount would scarcely affect t h e efficiency appreciably, i t is advisable t o subtract 6. o cc. from t h e volume f. Possibly a suitable oxidizer not yielding gaseous oxygen could be found, b u t i t hardly seemed worth while t o search. A point of advantage t h a t has great weight in practice is t h a t there is no limit t o t h e length of time during which a sample may be taken. If i t is desired t o take a sample continuously, i t is only necessary t o get a n aspirating bottle (or other vacuum device) large enough, and t o arrange sufficient capacity in t h e absorbers. Those who have worked with catalyzers will appreciate this point. The arrangements suggested are such t h a t it is possible t o make a test without dismantling t h e apparatus, t h e liquids t o be titrated, for example, being drawn off without disturbing t h e rest of t h e apparatus. Moreover, t h e sample may be taken a t a n y speed, say one bubble every five minutes, if i t should be desired t o make a test over a considerable period of time. An alternative a n d efficient absorbing medium for nitrous gases is sulfuric acid. As is t h e case with standard alkali, t h e gases must be previously mixed with oxygen as i t is nitrogen dioxide and not nitric oxide which is absorbed. A trial with d r y nitrogen peroxide a n d air with t h e writer’s apparatus, using concentrated acid in t h e first t u b e a n d standard alkali a n d hydrogen peroxide in t h e second, showed t h a t 98 per cent of t h e nitrous gases were absorbed in t h e first or sulfuric acid tube. Doubtless a n arrangement could be devised whereby only one t u b e would be required for complete absorption, so far as dry nitrogen peroxide is concerned. For ammonia oxidation exit gas, however, two tubes would seem t o be required as t h e acid in t h e first might become too dilute from t h e condensed water. For t h e determination both tubes would have t o be rinsed out with concentrated acid, all t h e acid mixed a n d diluted t o a known volume, a n d a n aliquot part taken t o be shaken out in a nitrometer. As this process is decidedly longer a n d less convenient t h a n t h a t with alkali a n d as t h e ammonia could not be determined in t h e sulfuric acid absorbent in a practical manner, no further experiments were made in this direction. Still, t h e method might be advantageous if i t was desired t o absorb large quantities of nitrogen peroxide, first cooling t h e gases thoroughly t o remove t h e water, in a separate apparatus. Plain water was also tried as absorbent medium, adding some hydrogen peroxide t o t h e second t u b e : a recovery of 9 2 . 4 per cent was obtained, from which i t is clear t h a t i t is necessary t o have t h e alkali. For t h e determination of ammonia in t h e exit gases, where t h e quantities are small,’ t h e most practical a n d available method is t h a t in which t h e ammonia is oxidized by sodium hypobromite, a n d t h e resulting nitrogen measured in a gas burette. By this procedure, using t h e solution which has been titrated with standard acid t o obtain t h e total nitrogen oxides, t h e ammonia can be estimated in 3 or 4 minutes. T h e 1 It would obviously be useless to make any sort of test, if large quantities of ammonia were escaping through the catalyzer unchanged.
741
method, due t o Knop, is described by Lunge,’ b u t a simpler apparatus can be used.2 Unless t h e temperature of t h e place where i t is used is uniform water jackets should be applied. Use 1 2 cc. sodium hypobromite solution ( 2 j cc. bromine and 1 5 0 g. sodium hydroxide in a liter) and I O O cc. of the solution taken from t h e first absorber, which has, of course, been titrated. If there is not so much solution, then use proportionately less sodium hypobromite, or, better, dilute so as to have nearly t h e same volume in each determination. The difference of readings is t h e nitrogen evolved, a n d doubling it t h e ammonia is obtained. There appears t o be no advantage is using more t h a n 1 2 cc. of sodium hypobromite solution. T h e results are much improved by making certain corrections. Around a plant where much ammonia is used, it is important t o make a blank either on t h e distilled water or on t h e standard solutions used. The author found t h a t this amounted t o 0 . 4 0 cc. Further, t h e amount of nitrogen evolved is less t h a n corresponds t o t h e ammonia, doubtless mostly on ‘account of t h e reaction not going t o completion. T h e correction t o be applied varies somewhat with t h e apparatus and conditions. For t h e writer’s conditions, t h e list of corrections given in the ChemikerKalender was found t o be of no use. T o find t h e corrections, prepare a N / I O solution of ammonium sulfate, a n d determine t h e ammonia in i t by t h e procedure described, using varying proportions up t o 2 5 cc. of t h e ammonium sulfate solution. The blank must be subtracted. Calculate t h e cc. of nitrogen t h a t I cc. of N / r o ammonium sulfate should yield at t h e temperature and pressure a t which t h e determination is made, using t h e formula v1 = 1 . 1 2
(I
+ 0.00367 t ) 760 b-e
V t is t h e volume of nitrogen corresponding t o
N/IOammonium sulfate, a t t h e temperature
I
cc. of t and
barometer b , where e is t h e tension of aqueous vapor corresponding t o t , all t h e pressures being in millimeters of mercury. Working in this way, i t will be found t h a t a fairly constant factor can be found between t h e theoretical a n d observed volumes, which may then be applied t o all results. This remark applies, of course, t o small amounts of ammonia, u p t o 3 j or 40 cc. T o calculate t h e efficiency consider any given volume, Ve, of entering gas mixture as made of four parts which may be conceived as independent strata. T h e first p a r t consists of t h a t portion which is destined t o react according t o t h e equation
NHa
+ I.
25 0 2 =
NO
As t h e oxygen comes from air
+ I . j HzO.
(1)
per cent oxygen) t h e nitric oxide is absorbed by t h e alkali, and t h e water condenses; 6.98 volumes of air-ammonia mixt u r e yield 4.73 volumes of gas (N2) in t h e aspirating bottle. Call this perfectly combusted p a r t or s t r a t u m (20.9
1 Lunge and Berl, “Taschenbuch fur die anorganisch-chemische Grossindustrie,” 1914, p. 255. Treadwell and Hall, 8 , p. 622. 2 Olsen, “Quantitative Chemical Analysis,” 1908, p. 317: apparatus consists o f a decomposition flask and gas burette.
T H E JOURNAL OF INDUSTRIAL A N D EXGINEERING CHEMISTRY
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V,, and on passing through t h e catalyzer a n d absorbersl i t shrinks from V, t o 0 . 6 7 8 T’c. The second p a r t or s t r a t u m is t h a t which reacts according t o t h e reaction X H B 0 . 7 j 0 2 = 0 . j N1 I . 5 H20. (2)
+
+
T h a t is, one volume of ammonia plus 3 . 59 volumes of air yield 3 . 3 4 volumes of nitrogen in t h e aspirating bottle. Call this second part, which yields nitrogen on combustion, V,. T h e V , on passing through The catalyzer and absorbers shrinks t o 0 . 7 2 8 TI,. third part is t h e excess of air, V u ,which passes through unchanged, and t h e fourth part is t h e excess of a m monia which passes through t h e catalyzer unchanged, b u t is absorbed in t h e absorption tubes. Call this lost ammonia VI. I n operating a furnace, it is of course advisable t o adjust i t so t h a t no ammonia escapes oxidation. Hence we first consider t h e case where there is no ammonia in t h e exit gas. If f is the volume collected in t h e aspirator bottle and f c t h e same volume corrected, as will be mentioned below, S O t h a t j c is t h e volume f would have if t h e correction proceeded according t o ( I ) and ( 2 ) without admixture of oxygen, and if the nitric oxide were directly removed by t h e absorbers, we have f c = 0 . 6 7 8 Vc 0.728 V , ?’a. (3 1
+
+
If b is t h e ratio of t h e ammonia t o t h e given volume T’, of entrance gas, 17nhs = b ( V c Vn Val, (2) where V,hs is t h e ammonia in Since one volume of ammonia yields one volume of nitric oxide
+
+
= 0.1433 V c , (3) where V,, is t h e volume of nitric oxide as calculated f r o m t h e titration, and V , contains 14.33 per cent of ammonia, which is t h e theoretical percentage for a perfect reaction. Also, considering t h e volume percentages of ammonia in V , a n d V n , we have Vnha = 0.1433 Vc 0.2178 V n . (4)
+
Eliminating V u between ( I ) and (2),
--fc b’nha
b
=
0 . 3 2 2 3 T/r,
+
0.
Eliminating 1,’ between (4) and l’nha
=
fc
f
0.
I/b-
(5)
(j),
I433 I’c I . 2 j
2723 trn.
.
(6)
Equations (5) and (6) are independently useful; ( j ) gives t h e contraction and (6) t h e total volume of ammonia used. Since V,, is directly known from t h e titration, we can easily get V,from (3). The efficiency is the volume of nitric oxide divided by t h e volume of ammonia.
It will thus be seen t h a t t h e calculation of a n efficiency is a good deal simpler t h a n might be supposed from t h e steps. The method does not necessitate t h e estima1 T h e catalyzer is of course t h a t of the plant being tested, and the absorbers those of the testing outfit.
Vol. 9 , KO. 8
tion of t h e oxygen in f . I n case t h e hypobromite or other test shows t h a t ammonia has gone through t h e catalyzer unchanged, t h e equations must be modified as follows: If V1 is t h e lost ammonia in Ve, and considering t h a t VI is a separate p a r t of 1’~and does not form part of Vc, Equation (3) remains unchanged, all t h e lost ammonia being absorbed. Since Vl is a p a r t of Ve,
+ +
Vnhs = b ( V c Vn J“a VI), (8) Since Vno is determined b y titration and does not include t h e nitric oxide neutralized by Vl, V,, Ti’ = 0.1433 Vc. (9) Equation (9) involves t h e assumption t h a t t h e plant is not operating with such gross inefficiency t h a t more ammonia is going through t h a n is being oxidized. I n this case t h e standard alkali in t h e absorbers would become more alkaline, a n d i t would not be worth while t o calculate t h e efficiency at all. Equation (4) must be modified as follows: V n h s = 0 . I433 v c 0.2178 Vn (10) Eliminating V, between (3) and (8),
+
+
+
‘nha-jc
= 0.3223 vc f 0.2723 V n b Eliminating V u between ( I O ) and (11),
+ Vi.
(11)
I n t h e efficiency equation, V1 must be added t o V,, as V1 neutralizes its equivalent of V,,, as determined b y titration. from (9),
Substituting
V, in known terms
The volume f is t h e final volume collected in the aspirator bottle at t h e temperature a n d pressure at which t h e experiment was made, or corrected for temperature a n d pressure if necessary. This volume f must be corrected ( = fc) because not only has oxygen been added, b u t a secondary reaction has taken place. The nitric oxide of Equation ( I ) has absorbed oxygen from t h e excess of air, V u , a n d from t h e oxygen added. Since one volume of nitric oxide absorbs one-half volume of oxygen, and since V n , is t h e nitric oxide as determined b y titration and does not contain a volume of nitric oxide converted t o ammonium nitrite or nitrate by t h e volume (V,) of ammonia escaping oxidation, we have t h e correction fc = j 0.5 (Vno VI)- Vox, where V o x is the volume of oxygen added. If t h e oxygen content of t h e gas in t h e aspirator bottle is determined, V u may be found from i t as a check, or a different method of calculating t h e efficiency might be adopted-but both these necessitate t h e determination of oxygen. I n any case, i t is useful t o have t h e gas divided into components according to they way they act t o t h e catalyzer and absorbers. I n t h e above discussion no mention has been made of aqueous vapor. It is obvious t h a t its effects will, in t h e efficiency ratio, partly cancel out, b u t not entirely. I n case a degree of accuracy is required such
+
+
A w . , 1917
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
t h a t t h e aqueous vapor must be t a k e n into account, there is nothing t o do b u t make t h e necessary corrections in each quantity a s found-which is more simple t h a n making a new set of equations. It seems t o be true, as first observed b y Berthelot,’ t h a t nitrogen trioxide is first formed b y t h e interaction of nitric oxide and oxygen even when t h e oxygen is in excess, b u t t h e nitrogen dioxide is so quickly formed t h a t there is no danger of error from this source. Only traces of nitric acid are formed a t t h e dilution of t h e gases used, though if pure oxygen and pure nitric oxide are mixed, larger quantities m a y result. These reactions in no way affect t h e titrations. and only t h e final volume as a small correction t o a large volume. I n experimental work t h e total ammonia consumed can be found b y titrating t h e liquor used for s a t u r a t ing t h e air (if t h e air is saturated b y this means) before a n d after t h e experiment. B u t this is of course impossible in a manufacturing plant, since t h e intake a n d exit gas are sampled only, not taken as a whole. For t h e nitrous acid, t h e most practical method for t h e case in h a n d is b y t h e use of permanganate. I n the procedure devised b y Lunge,2 t h e nitrous acid sample is placed in t h e burette a n d r u n into a measured excess of permanganate heated t o 40-50’. T h e color change is not very prompt, a n d t h e method is inconvenient unless the approximate a m o u n t of nitrous acid is known. B y working in t h e following way t h e results are obtained more quickly, t h e approximate q u a n t i t y of nitrous acid need not be known, andwhat is a matter of importance in some plants-no flame or heat is required. Prepare a dilute solution (about I volume of 3 yohydrogen peroxide t o 7 volumes of water) a n d t i t r a t e i t with permanganate. d d d a measured quantity, s a y I O cc., of this solution t o t h e nitrous acid sample, a n d t i t r a t e with permanganate. T h e nitrous acid is readily calculated from t h e difference. E v e n if t h e hydrogen peroxide had t o be titrated for every determination, t h e method is more satisfactory t h a n t h e direct use of permanganate. Of course t h e same assumptions are valid as t o t h e presence of other oxidizable bodies, etc., as with t h e direct use of permanganate. 1605 EASTCAPITOL ST. WASHINGTOS, D. C.
THE EFFECTS OF EXPOSURE ON SOME FLUID BITUMENS By CHARLESS. REEVE AWD RICHARDH. LEWIS Received April 16, 1917
I n 1912, Hubbard and Reeve published a paper3 giving t h e results of exposure on some semi-solid bitumens, a n d this was later followed b y a paper4 b y Reeve a n d Anderton in which t h e effects of exposure 1
Compt. r e n d . , 67 (1873), 1450.
* Lunge,
“Sulfuric Acid and Alkali,” 4th E d , 1 (1913), 3 8 i . See also especially Gerlinger, Z . angew. Chem., 1901, p. 1250. 8 “The Effect of Exposure on Bitumens,” THISJOURXAL, 6 (1913), 15. A paper presented a t the Eighth International Congress of Applied Chemistry, New York, September, 1912. “ T h e Effects of Exposure on T a r Products,” J . Frank. Inst., October, 1916.
’
743
as limited t o t a r products were shown a n d some of t h e relations between t h e results of exposure a n d laboratory tests were discussed. I n view of t h e interesting behavior shown b y t h e various products considered in t h e above investigation, t h e authors felt t h a t further results of value might be brought o u t b y continuing a similar line of investigation t o show t h e behavior of more fluid materials. T h e form of investigation is, moreover, more directly related t o materials of this character, owing t o t h e fact t h a t t h e y are largely used in surface treatment where t h e y are directly exposed in a thin layer t o t h e action of sun and air. T h e exposures were made in a box of t h e same t y p e as t h a t used in previous work and shown in Fig. I.
FIG. I
For t h e information of those who are not familiar with t h e earlier publications on t h e subject, t h e following brief description of this box is given. It is made of 3/4-in. wood and has interior dimensions 2 j X 14l/2 X 2 in. A ‘/d-in. plate glass cover rests on a strip of thick felt fastened t o t h e edges of t h e box in order t o make a tight joint and exclude all dust. For ventilation, slots are cut through each side of t h e box, and t o prevent t h e entrance of rain these are protected b y a thin board extending from t h e rim a t an angle of about 45’. Cotton batting is packed under this board against t h e slots t o exclude dust from t h e outside air. T h e samples t o be exposed were placed in 2 - 0 2 , , seamless, flat-bottom, tin boxes, having a diameter of 6 cm. and a depth of 2 cm. I n order t o insure a uniform depth of sample, approximately 1 2 cc. of t h e material under test were used. Seven rows, each consisting of six boxes of t h e same material, were placed lengthwise of t h e box, which was set with its long side extending east and west outside a window having a southern exposure. T h e m a t e r i d s used and their characteristics are given in Table I. All tests made in connection with this work v e r e carried out as described in Office of Public Roads Bidleti?i 38.’ T h e samples were exposed on J a n u a r y 7 , a n d a t t h e end of every second month a complete set ~ 7 a s withdrawn a n d tested, until t h e exposure had r u n throughout a full year T h e tests a t t h e end of each period included a careful weighing t o note a n y loss or gain, a consistency test, and t h e determination of organic matter insoluble in carbon disulfide, and fixed carbon. Where possible, penetration tests were made on t h e residues from exposure; othenvise, t h e consistency was determined b y a float test a t 40’ C. f “Methods for the Examination of Bituminous Road Materials,” b y Prevost Hubbard and Charles S. Reeve
