ISDCSTRIAL A S D EXGIIVEERI~YGCHEMISTRY
970
T a b l e V-Composition,
H i d i n g Power, Visibility, and E n d u r a n c e of T y p i c a l T r a f f i c Paints (Concluded) .-HIDING
Paint
76
Pigmentvehicle ratio
71:29
Size of inert particles Microns
--Pigment---
“ X X ” zinc oxide B. S.L. Talc
T’ol. 18, s o . 9
POWSR~-
Computed at 80% Bright- Relative brightness ness Sq. ft./ Sq. ft./ VISIBILITY gal. Per cent gal. Night Day
Vehicle
21% 49% 30 %
79.0
260
248
9.0
12.5
Corn. A 57:43b
Lead chromate Lead sulfate Inerts
3770 9% 54 %
All finer than Unknown; contains 150 65Y0 volatile. Slow drying required 5 hours t o dry tack-free
54.5
401
178
1.2
9.2
Corn. B 67:33b
Zinc oxide B. S. L. Inerts
37%
All finer t h a n Unknown; contains 150 60% volatile
73.8
256
195
2.0
11.0
Lithopone Inerts
60%
hpprox. 5057, Unknown: contains larger t h a n 75% volatile
85.2
192
Com. C 68:32b
18%
45% 40%
260
11.0
150
12.6
Effect of Combined Accelerated Weathering and -4brasion Test Considerable chalking; n o cracking, peeling, o r breaking away of coarse particles; fair resistance t o abrasion. T h e paint showed a brown discoloration Very heavy chalking; no cracking or peeling; very poor resistance t o abrasion; uneven discoloration to orange and red-brown Very heavy chalking: no cracking 01 peeling; very poor resistance t o abrasion C:onsiderable chalking. no cracking or peeling.’ some breaking away ok coarse particles; film, appears porous: poor resistance to abrasion
b Probable composition (by analysis).
Extinction of Methane-Air Flames b y Some Chlorinated Hydrocarbons’” By H. F. Coward3 and G . W. Jones4 PITTSBLRGH EXPERIMENT STATION B,U R E A UO F MINES, PITTSBURGH, PA
The nature of the extinctive action of inert gasesH E extinctive effect of sufficed to raise the Iower carbon dioxide, nitrogen, argon, helium-on flame has limit of methane nearly 2 per i n e r t gases on methbeen e!ucidated by the determination of the limits of a n e - a i r f l a m e s has cent, whereas we should not inflammability of methane in atmospheres composed r e c e n t l y b e e n studied by expect, on the thermal conof air mixed with increasing amounts of inert gas. siderations just mentioned, ineans of determinations of A new series of results, now presented, shows the inthat the lower limit would b e the limits of inflammability fluence of the vapors of certain chlorinated hydrocaraffected to the extent of more (lower and higher) of methane bons on the inflammability limits of methane in air. than a fraction of one-tenth in atmospheres composed of A comparison of the fire-extinguishing properties of of 1 per cent. ordinary air mixed with incarbon tetrachloride and carbon dioxide is included. If Jorissen’s experiments creasing amounts of carbon are right, he has discovered dioxide, nitrogen, argon, a i d helium. The limb of inflammability approached nearer some extraordinarily powerful fire-extinguishing agents. The and nearer as inert gas was added in increasing proportions writers have therefore made a thorough reexamination of the t o the atmosphere, until finally they coincided. The experi- influence of certain chlorine deriyatives of methane, ethane, mental results shown in Figure 1 led t,o the conclusion that and ethylene, on the limits of inflammability of methane. the relative extinctive effects of carbon dioxide, nitrogen, For this purpoie they have not followed Jorissen’s experiand argon are explained by their relative heat capacities, mental procedure, and it is therefore neceqsary to state in the gas of greater heat capacity having the greater extinctive some detail their criticisms of his work. He used three action. The abnormal behavior of helium, which has a similar vnall (3bcc.) burets with sonievhat different spark thermal capacity equal t o that of argon, was ascribed to its gaps at the top, so that downward propagation of flame was observed in each case. For inethane the lower limits for the exceptionally high thermal conductivity. In the light of these conclusions, some recent results of three burets were 5.4, 3.7, and 4.9 per cent methane, reJorissen6 and his co-workers are exceptional. They found, spectiT-ely. This inconsistency proves that Jorissen was not for example, that the presence of less than 1 per cent of the observing whether or not his mixtures were capable of propavapor of tetrachloroethylene or tetrachloroethane in air gating flame per se. His apparatus is not satisfactory to insure certain ignition and also to give the resultant flame Presented before t h e Section of Gas and Fuel Chemistry a t the 7 l s t a long enough “run” to enable observers to judge whether i t Meeting of the American Chemical Society, Tulsa, Okla., .4pril 5 t o 9, 1926. 2 Published with approval of the Director, U. S. Bureau of Mines. is self-propagating when it has lost the initial impulse due T h e work reported in this communication forms part of the program of to the source of ignition. cooperative work between the Bureau of Mines (U. S. .Iand .)the Safety Jorissen’s failure to appreciate the experimental requisites in Mines Research Board (Great Britain), and was undertaken during the in this type of work is further illustrated by the following visit of one of the writers t o the Pittsburgh Experiment Station of the Bureau. quotation from his first paper:
T
1
Principal assistant, Safety in Mines Research Board, Great Britain. Associate chemical technologist, U. S . Bureau of Mines, Experiment Station, Pittsburgh, Pa. 5 Coward a n d Hartwell, J . Chem. S O L . ( L o n d o n ) , 129, 1522 (1926). 8 Rec. t m v . chim., 43, 80, 591 (1924); 44, 132 (1925). a
4
From Bunsen’s observations on the explosibility of hydrogen oxygen mixtures a lower explosion limit of about 6 1 vol. per cent may be calculated. When we compare this limit with t h a t for hydrogen air mixtures as determined by J. Roszkowski, viz.:
September, 1926
I,YDL7STRIAL A S D EATGINEERINGCHE-MISTRY
9.5 vol. per cent, we note the considerable influence of nitrogen. For the proportion between the concentrations of hydrogen and 6.1 9.50 oxygen has been incremed from - t o -. 93.9 19
The comparison between Bunsen's observaticins on hydrogen-oxygen mixtures with Rosakowski's on hydrogen-air mixtures involves other variables, the explosion vessel and the means of ignition. It is unnecessary so t o complicate matters, for Roszkowski himself made a direct comparison between the loTT-er limit of hydrogen in air and in oxygen, finding them to be 9.5 and 9.7 per cent, respectirely. (For upn-ard propagation of flame the lower limit of hydrogen in air or in oxygen is just above 4 per cent.) Hence in comparable experiments the influence of nitrogen in this example is inconsiderable. Experimental
In order to observe the limits of inflammability of gas mixtures it, is necessary to use sufficiently powerful means of ignition, in a vessel sufficiently long and wide. A vessel that is too narrow will cool and extinguish some weak flames which would be readily propagated in wider vessels. Constant' pressure must be maintained during the progress of the flame, for limits of inflammability are markedly influenced by such changes of pressure as occur during propagation of flame in a limit mixture contained in a closed v e ~ s e l . ~I t is desirable, whenever possible, to determine limits for propagation of flame upward rat,her than downward (there is a marked difference--.e. g., hydrogen, lower limit, 4.1 per cent and about' 9 per cent, respectively), for theoretical reasons as well as for such practical reasons as safety in mine atmospheres and fire extinction.6 As satisfying the foregoing requirements the writers chose a glass tube 5 feet long, 2 inches internal diameter (Figure 2), ignition of each trial mixture being effect'ed by sliding away a ground-glass plate, s, and immediately drawing the flame of a small spirit lamp across t'he open end of the t,ube. The chief difficulty lay in filling the tube with mixtures of predetermined composition; for the vapors of the chlorine compounds used are soluble in rubber and in all tap lubricants which will hold a vacuum. Several devices developed in the Bureau of Mines for other purposes were used and so arranged that a homogeneous stream of methane and air of known composition was passed through a tube to Tyhich was supplied a steady amount of the liquid chloro compound, which mas evaporated regularly. I n Figure 2, e and e' represent flowmeters for insuring the desired supply of air and methane, respect'ively ; these gases were mixed in g and at p picked up the vapor, x-hence they passed to the observation tube, I-. Procedure Air was introduced through a drying tower, a, passed through the T-piece b and flowmeter e t o meet a t g the supply of methane which had passed through a similar T-piece b' and flowmeter
e'. The T-pieces, dipping under water to a depth which could
be regulated as required, served to maintain constant rates of flow of the gases through the flowmeters by acting as relief valves for excess of gas. For the flowmeters, capillary tubes f and f ' of suitable size were chosen by trial. The flowmeter for air, measuring rates u p t o one liter per minute, was calibrated by a standardized wet meter. The flowmeter for methane was calibrated to read directly the percentage of methane in the mixture made a t g , when the rate of flow of air was one liter per minute. Samples of the flowing mixture were taken a t T-piece h into the vesselj by allowing the mercury to run slowly from j into the reservoir k ; the samples were passed through 1 into the sampling tube n, whence they were analyzed over mercury in a Bone and Wheeler appaMason and Wheeler, J . Chem. SOC.(London), 113, 4 5 (1918). 8 For a more complete discussion of these points see Coward and Brinsl e y , I b i d . , 106, 1859 (1914). 7
971
r a t ~ s .From ~ the analytical results a scale on the methane flowmeter was constructed t o read directly the percentage of methane in the methane-air mixtures. The flowmeters were used to facilitate the production of desired mixtures; the actual composition of the methane-air mixtures sent forward t o the observation tube was determined by analysis of a sample taken in the same manner as for the calibration. The stream of methane and air was readily kept of constant composition, within 0.10 per cent methane, for several hours.
Introducing Chlorinated Hydrocarbon Va'apors into Methane-Air Mixture The chlorinated hydrocarbon vapors were introduced into the stream of methane-air by Yant and Frey's method,I0 modified slightly t o meet somewhat different conditions. It was found necessary t o surround the storage bulb t of the liquid chlorine compound with a water bath, t o maintain a uniform temperature. A three-way stopcock, d, was added t o facilitate changing from one compound t o another. The rate a t which water flowed from the reservoirs w and w' governed the rate of expulsion of liquid from t , and hence the rate of vapor production in P . At rates up t o 40 drops per minute the drops of water from w were equal in size, hence the rate of supply of vapor was proportional to the number of drops of water falling per minute; but a t higher rates the drops became smaller. For low rates of dropping the delivery of chlorine compound was therefore determined by counting the drops, after suitable calibration; for higher rates the cylinder u was graduated and the rate of delivery of chlorine compound determined, for each compound separately, from the time taken to raise the water level over a height corresponding to 25 CC. This necessitated two calibrations for each liquid compound, one by Yant and Frey's method, the other for the higher rates; the latter was made by careful measurement of the liquid compound expelled a t p when registered amounts of water were dropped into u. ,.?
I
0
OXYGEN IN ORIGINAL RTMOJPHERE, PER CENT I4 13
. . . . . 1.9. . . . .10. . . . .17. . . . . 16. . . . . .IS.
I
5
IO
I IS
j.
CARBON DIOXIDE NITRoGEN ARGON
I
I
25
I2 I '
, , / . , . , I "
I 30
I
I
35
40
I1
10
" ' , ' " ' , ' ' ~
I
45
50
55
IN ORiGlNAL AMOSPHCRE~PER CENT
HELIUM
Figure 1-Limits
of Inflammability of Methane i n Atmospheres of Air Mixed with Certain Diluent-Gases
The vapor content of the gases was checked by analysis in a n apparatus similar to t h a t designed by Burrell and Robertson" for the determination of benzene vapor in gas mixtures. The mixture was sampled from a point a few inches above the lower end of 7 (Figure 2 ) into an evacuated bulb (Figure 3), the vapor frozen out by means of liquid air, the air and methane removed by the pump, and the bulb then warmed to room temperature and the pressure of the evaporated vapor measured. The only essential alterations from Burrell and Robertson's apparatus were the elimination of phosphorus pentoxide and the use of a special form of stopcock which, by virtue of a mercury seal around the plug and barrel, and a mercury seal through the bore of the 9 The most recent, and most detailed, account of this apparatus is t h a t by Grice and Payman, Fuel, 3, 236 (1924). 10 THIS JOURNAL, 17, 692 (1925). " I b i d . , 7, 669 (1913).
972
INDCSTRIAL A X D EXGINEERI-VG CHEMISTRY
plug, was capable of holding a vacuum without lubricant. It was found t h a t the vapor content of a mixture could be maintained constant within 0.5 per cent a t the highest concentrations used (about 13 per cent). Some of the chlorinated hydrocarbons used were toxic. To prevent their vapors getting into the air of the room a funnel was placed around the discharge end of the tube r and the gases were drawn through a canister containing a suitable absorbent.
Test of Inflammability For an actual experiment on inflammability, the air, methane, and chlorinated hydrocarbon supplies were adjusted and the whole mixture passed through the mercury-sealed joint, q , into the explosion tube, 7 . This was swept out for 15 minutes, the glass plate s being moved a little t o one side t o make an exit orifice. Samples of the mixture were taken for analysis. The
Figure 2-Inflammability
Boiling point Pentachloroethane, “technical” s-Tetrachloroethane Perchloroethylene Trichloroethylene s-Dichloroethylene Carbon tetrachloride
c.
143 to 161 (70 per cent distilled over a range of 2’ C . ) to 146 to 121 to 87 to 60 to 7 6 . 3
144 119 85.5 56 76.1
Results of Experiments
Limits of InJEammability of Methane in Air The limits Observed in the apparatus described were, for gases roughly dried by calcium chloride, 5.24 per cent methane (lower) and 14.02 per cent (higher), plus or minus 0.02 per cent. Limits i n Air Containing Pentachloroethane Vapor Air saturated with pentachloroethane vapor at laboratory temperature Was found to contain 0.6 per cent (by volume).
Limits Apparatus for Mixed Gases and Vapors
flow through r was then stopped by raising z and closing s. For the moment, until the supply of gases and vapor could be stopped, the stream escaped through the mercury at q. The inflammability of the mixture in r was then tested, as described, by sliding away the ground-glass plate s and immediately drawing the flame of a small spirit lamp across the open end of the tube. The composition of the mixtures was changed from one test to another until a mixture was found which would propagate flame throughout the tube and another, of slightly different Composition, which would fail t o propagate flame more than a foot or so up the tube. The mean composition of the two mixtures was then plotted as a limit point on the diagram (Figure 4). The saturation points of most of the vapors were reached a t a n early stage, and in these cases the curves extend t o saturation on both lower and higher limits. For carbon tetrachloride and dichloroethylene (acetylene dichloride) only was it possible to make complete curves a t laboratory temperature (20-25’ C.). The abscissas in Figure 4 represent the volumetric composition of the methane-free “atmosphere” composed of air mixed with the indicated proportions of diluent (chlorinated hydrocarbon or carbon dioxide). The ordinates represent the amounts of methane which, in these atmospheres, form lower and higher limit mixtures. The chloro derivatives used were Eastman chemicals, and were ascertained t o agree with the maker’s description: 0
Vol. 18, s o . 9
I n this “atmosphere” 5.30 per cent methane and 5.40 per cent propagated flame at a uniform rate throughout the tube described. These results were confirmed by repetition. A 5.14 per cent methane mixture failed to propagate flame. The lower limit for methane in this atmosphere is therefore about 5.2 per cent, not appreciably different from that i n pure air. The upper limit in the same atmosphere was 13.6, and 13.8 when the air was half saturated with the chlorine compound. These results may be compared with those obtained when carbon dioxide and carbon tetrachloride vapors are present (Figure 4) and show that pentachloroethane is in no way exceptional as a flame-quenching agent.
Limits in Air Containing Tetrachloroethane Vapor Air saturated with tetrachloroethane vapor contained 1.0 per cent of the latter (by volume) and gave an inflammable mixture with 5.5 per cent methane, not with 5.3 per cent. The upper limit was 13.0 per cent. This chloro derivative is therefore, also, not exceptional as a flame-quenching agent. Limits in Air Containing Tetrachloroethylene Vapor The limits of methane, in atmospheres containing tetrachloroethylene vapor up to the saturation amount at laboratory temperatures, are shown by two curves in Figure 4. From these we see that the lower limit is decreased and conclude that the vapor contributes by its combustion to the heat
INDUSTRIAL A'\-D
September, 1926
ENGINEERING CHE-IIISTRY
of the flame and so assists propagation. The rather rapid fall in the upper h i t may doubtless be ascribed to the same effect superposed on the ordinary effect of a diluent such as carbon dioxide, which depresses the upper limit by virtue of ( a ) the decrease in oxygen due to the addition of the inert gas to air, and (6) the higher heat capacity of the inert gas. I 1
973
L i m i t s in Air Containing Carbon Tetrachloride V a p o r
Figure 4 contains the observations of the effect of carbon tetrachloride on the limits of methane. The curve is of the normal type for a vapor which takes little or no part in the development of heat on the burning of the methane. For comparison, part of the corresponding curve for carbon dioxide is included. The greater heat capacity of carbon tetrachloride accounts for its greater extinctive effect. It appears that, at laboratory temperature and pressure, a mixture of air and carbon tetrachloride containing 12.5 per cent of the latter is incapable of propagating flame when mixed with any amount whatsoever of methane. The corresponding figure for carbon dioxide is 25 per cent and these figures arc fairly closely in the inverse ratio of the heat capacities of the two substances, at constant pressure. Compuratiae E.~ti?icti~~e I-alue of Carbon Tetrachloride and Carbon Dioxide
10 1
Figure 3-Analysis
Apparatus (Sh
ng Special Taps)
Volume for yoluine. therefore, carbon tetrachloride vapor is twice as extinctive as carbon dioxide. The molecular weight of carbon tetrachloride is, however, about 3.5 times that of carbon dioxide. Hence, weight for weight, carbon dioxide is nearly twice as extinctive as carbon tetrachloride. Carbon dioxide liquid is, however, of just about half the density of carbon tetrachloride; hence equal volumes of the two liquids have nearly equal extinctive action.
I n view of this analysis. the effect of tetrachloroethylene is not abnormal; the experimental results show far less effect than was claimed by Jorissen.
Limits in A ir Containing Trichloroethyle ?e T'apor The curves in Figure 4 show the effect of trichloroethylene vapor on methane limits in amounts up to saturation. Evidently. the vapor contributes to the heat of combustion, and by reducing the lower limit of methane substantially would contribute to the danger of inflammation. L i m i t s in A i r Containing Dichloroethylene V u p o r This substance is so volatile that complete curves for both lourer and higher limits of methane Tyere obtained (Figure 4). It is evident that dichloroethylene alone makes inflammable mixtures with air. The writers found its limits to be 9.7 and 12.8 per cent. I t is not surprising, therefore, that Jorissen was unable to obtain any inflammable mixture of methane with a 20 per cent mixture of this compound in air. A simple relation has been found to hold, in some cases, between the limits of two inflammable gases. individually observed, and the limits of mixtures of the t a o gases. LeChatelier expressed the relation thus:
where N1 and X2 are the lower limits, in percentages of the whole air mixture, for each combustible gas separately; nl and nz are the proportions, in percentages of the whole air mixture, of each combustible gas at the dilution limit. This formula, with the addition of more terms when necessary, has been proved to hold with approximate accuracy for upper as well as lower limits in the case of hydrogen, carbon monoxide, and methane mixtures.l? More recently, White13 hac found marked exceptions in other examples; to these may now be added the series of mixtures of methane and dichloroethylene, the divergence of which from LeChatelier's rule is shown in Figure 5 . The points in this figure represent the same expwimental observations as are plotted in Figure 4, expressed on a different basis. l2
Coward, Carpenter, and Payman, J
Chem Soc (London), 116, 27
(1919) l3
I b i d , 121, 2561 (1922)
137, 48 (1925).
Factors other than thermal data have to be considered in assessing the relative values of these two fire-quenching agents. For example. the superior density of carbon tetrachloride vapor is an advantage, but the formation of poisonous gases, including phosgene, makes it "dangerous to breathe the gases that may be generated from one quart of carbon tetrachloride extinguisher applied to a fire in a confined space (say 1000 cubic feet) from which escape is difficult or impossible. and from which the gases would not be removed by
. INDUSTRIAL A X D ENGINEERING CHEMISTRY
974
Vol. 18, No. 8
chlorinated hydrocarbons on the limits of inflammability of methane in air.
v e n t i l a t i ~ n . ” ’ ~On the other hand, liquid carbon dioxide partly solidifies on evaporation and care must be taken to prevent choking the jet of the container from which the gas is issuing; and the formation of poisonous concentrations of carbon monoxide is possible in fighting fire with the dioxide.
Summary a n d Conclusions
The limits of inflammability of methane in atmospheres composed of air mixed with the vapors of C&IC15, C2H2C14, CaC14, CZHC13, CzHzC12, and CClk have been determined, for amounts of vapor ranging from zero to saturation a t laboratory temperature (20-25” C.), or to such a concentration that an “atmosphere” is formed which will not propagate flame whatever proportion of methane be mixed with it. The results, represented in part in the curves of Figure 4, show that the two ethane derivatives behave like inert dilueats, the effect of which is to be attributed to their thermal capacity. The ethylene derivatives contribute to the inflammability of the mixture by causing a fall in the lower limit of methane with increase in the proportion of vapor; the effect on the upper limit also is a contribution of material which burns in the methane-air flame; in both cases the order of increasing combustibility is C2C14+ C2HC13+ C2H2C13,and in the last case this vapor forms inflammable mixtures with air, without the help of any methane. The extinctive effect of carbon tetrachloride on methane flames is, so far as our imperfect knowledge of its specific heat permits us to conclude, entirely due to the cooling action which its high thermal capacity makes so marked.
Some Attempts t o Reproduce Jorissen’s Results
As the results obtained were so completely a t variance with Jorissen’s, especially those relating to the influence of one per cent or less of the vapor of some of the heavier chlorinated hydrocarbons, the writers replaced the observation tube r by a n imitation of Jorissen’s. This was 25 cm. long, 1.6 cm. internal diameter, with platinum electrodes giving a 5-mm. spark a t the top. At the bottom was a stopcock which was closed just before an observation was made. The most critical comparison is that between the results for tetrachloroethylene, because Jorissen claimed that \Then 0.7 per cent of this vapor was added the lower limit of methane
Utilization of Energy ULTIMATE FORMS METHODS OF CONVERSION
RAWMATERIALS A
OF ~ T l L I Z A T l O N
Electrochemical Burnine
Coal
I
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so
60
70
80
9o
loa
I
60
50
40
30
20
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(1)
Figure & L i m i t s of I n f l a m m a b i l i t y of M i x t u r e s of M e t h a n e and D i c h l o r o e t h y l e n e w i t h Air
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was raised from 5.4 to 7.35, while in the writers’ large tube the curve (Figure 4) indicates a fall from 5.24 to about 5.15 per cent for the same amount of vapor. I n the small “imitation” tube the lower limit of methane alone in air, downward propagation of flame, was 5.72 per cent, and as tetrachloroethylene vapor was added the limit fell until at saturation (2.5 per cent) the limit was 5.48 per cent methane. This observation mas confirmed, qualitatively, by adjusting the methane-air mixture so that in the absence of tetrachloroethylene flame would not propagate, yet when tetrachloroethylene vapor was introduced the mixture would propagate flame throughout. This was repeated several times. It was then thought possible that Jorissen’s observations might be caused by the presence of liquid chlorine compound on the walls of the tube and perhaps on the spark wires, and that this would vaporize during the experiment and thereby produce a high concentration of extinctive vapor. To test this hypothesis, some of the compound was distilled into the explosion tube and allowed to condense on the walls and wires. I n repeated attempts, however, no difference was made to the observations. The writers have been driven to the coiiclusion that Jorissen has much overestimated the effect of small amounts of 1’ Fieldner a n d others, J. Franklrn Insl , 190, 543 (1920); K a t z a n d others, Bur. Mines, R e m . Inveslrgatzons 2499 (1923).
l
-
I
I Gasoline
Chemical Uses (Steel Manufacture, etc.)
I Shale
Gasoline
Natural Gas Chemical Products
-..-Future
Developments
(1) Bergius process (2) Fischer process (3) Cracking process
Oil Shale Dust Explosive Tests conducted at the Pittsburgh, Pa., experiment station of the Bureau of Mines, Department of Commerce, have demonstrated t h a t oil shale dusts are explosive, and that their explosiveness increases with their combustible content. The formation of dust during the mining and handling of oil shale is almost unavoidable, and the Bureau considers that the same precautions against dust explosions should be taken in the industries working with oil shale as are taken in safely operated coal mines.
