May,
IgIj
T H E J O U R , V A L O F I S D C S T R I A L d LVD E ;VGI ATE E RI LYG C H E M I S T R Y
is t h e h e a t of combustion a n d t h e percentage of gasoline vapor required t o furnish this q u a n t i t y of heat. S U 31 M A R Y
Using a I O O cc. Hempel explosion pipette a n d igniting t h e mixtures from t h e t o p , there was obtained as t h e lower limit (of complete inflammation a value lying between 1 . 9 a n d 2 . 0 per cent of gasoline vapor. T h e upper lim t under these conditions was found t o be between j . z a n d 5.3 per cent of gasoline vapor. T h e gasoline used h a d a specific gravity of 73' Baumk. Under t h e same conditions. except ignition of t h e mixtures f r o m t h e b o t t o m , there was obtained a value lying between 1.5 a n d 1.6per cent of gasoline vapor as t h e low limit. With t h e s a m e grade of gasoline, using a 2800 cc. vessel, a n d with ignition from t h e b o t t o m , b y means of a n electric flask produced b y pulling t w o wires a p a r t through which a current of 7 amperes a t 2 2 0 volts was flowing, there was obtained a value lying betn-een 1.4a n d 1.5 per cent of gasoline vapor. T h e high limit under these conditions l a y between 6.0 a n d 6.4 per cent of gasoline vapor. Appreciably different limits were n o t obtained with vapor from cleaners' n a p h t h a . When t h e initial t e m p e r a t u r e is increased before igniting t h e mixtures t h e low limit is gradually decreased until, with a n initial temperature of A,OO' C., t h e low limit lies between 1 . 0 2 a n d 1 . 2 2 per cent of gasoline vapor.
417
t h e free e n d of t h e stop-cock a n d t h e oven heated t o t h e required temperature, whereupon t h e gas mixt u r e was introduced into A a n d sparked after t w o seconds h a d elapsed. T h e flame produced, if a n y , was observed a n d t h e products of combustion analyzed. Preliminary experiments were performed with a thermo-couple inserted i n t h e explosion vessel A , t o determine t h e t i m e i t took t h e gas after i t was introduced into t h e evacuated pipette t o reach t h e temperature of t h e oven. I t was found t h a t this took
CAEMICAL LABORATORY, BUREAUOF MINES, PITTSBURGH
THE INFLUENCE OF TEMPERATURE AND PRESSURE ON THE EXPLOSIBILITY OF METHANE-AIR MIXTURES' B y G . A BURRELL A K D I . W. ROBERTSON Received December 15, 1914
I n this paper are shown t h e results of experiments made t o determine t h e effect of temperature a n d pressure on methane-air mixtures in changing t h e low limit of complete propagation of flame in mixtures. Temperatures u p t o j o o o C. a n d pressures of j . 0 atmospheres above atmospheric pressure were employed. T h e a p p a r a t u s is shown i n Fig. I . A is t h e explosion pipette. It h a d a capacity of I O O cc. P l a t i n u m wires were fused into t h e upper p a r t . ,4 s p a r k from a n induction coil, driven b y 4.o d r y cells, was used t o ignite t h e gas mixtures. ,4n electrically heated oven, D , surrounded t h e explosion pipette A . T h e temperatures were measured b y means of a platinum-rhodium thermo-couple. Transparent mica plates were used t o close t h e upper e n d of t h e oven in order t o observe t h e effects of sparking t h e mixtures. At B is shown a reserve pipette of zoo cc. capacity fastened t o t h e explosion pipette b y means of pressure rubber t u b i n g with mercury as t h e confining fluid. T h e a p p a r a t u s was made ready for use b y raising t h e leveling bottle C, thereby completely filling t h e pipettes A a n d B with mercury. T h e leveling bottle was t h e n lowered until all of t h e mercury h a d fallen from A , leaving a v a c u u m therein. T h e stop-cock between t h e t w o pipettes was t h e n closed. T h e required gas mixture was t h e n drawn into B through 1
Published with permission of the Director of the Bureau of Mines.
FIG.
1-APPARATUSFOR DETERMINING THE INFLUENCE O F TEMPERATURE PRESSURE O N THE EXPLOSIBILKTY OF METHANE-AIR MIXTURES
AND
place in less t h a n t w o seconds a f t e r t h e introduction of t h e gas. Methane was prepared from t h e n a t u r a l gas used at Pittsburgh b y fractional distillation a t low temperatures. T h e n a t u r a l gas was liquefied a t t h e temperat u r e of liquid air a n d as much gas p u m p e d from i t with a mercury p u m p as possible. The distillate was reliquefied a n d pumped again. A trace of nitrogen a n d pure methane t o t h e extent of a b o u t 8 j . o per cent of t h e original volume of t h e natural gas was obtained in this manner. T h e results of t h e experiments are shown in Table I .
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Experiments I t o j show t h e displacement of t h e lower limit of complete propagation with t h e initial temperature a t joo' C. a n d t h e initial pressure a t I atmosphere. As far as t h e eye could judge, there was a complete filling of t h e explosion vessel with flame when mixtures containing 4 . 0 0 t o 4 . 4 7 per cent methane were sparked. However, a measurable amount of methane remained unburned, probably due principally t o t h e fact t h a t a small amount of gas TABLEI-EFFECT OF INCREASING THE INITIAL TEMPERATURE ON THE Low LIMIT OF COMPLETEPROPAGATION OF FLAME IN METHANEAIR MIXTURES Tem- Pres- ANALYSIS OF MIXTURES Limits pera- sures. Before After per Test ture Atmos- sparking. sparking. cent No. C. pheres CH4 Air Observations CH4 CHI C o r 1 500 1 4 47 95.53 0 . 5 8 4.08 Complete propagation 2 500 1 4.27 95.73 0 . 6 4 3.85 Complete propagation 4 . 0 0 3 500 1 4.00 96.00 0 . 8 9 3.14 Complete propagation and 4 500 1 3 . 7 5 96.25 3 . 4 5 0.42 S o propagation 3.75 5 500 1 3 50 96.50 3.42 0 . 1 8 hTo propagation 6 400 1 4.75 95.25 0 . 7 5 3.74 Complete propagation 6a 400 1 4 . 5 5 95.45 0.65 3 . 9 3 Complete propagation 7 400 1 4.47 95.53 4 . 2 6 0.41 No propagation 4.55 8 400 1 4.27 95.73 4.12 0.23 Nopropagation and 9 400 1 4 . 0 0 96.00 3 . 8 8 0.20 No propagation 4.77 10 400 1 3 . 7 5 96.25 3.65 0.20 No propagation 11 300 1 5.15 94.85 0 . 8 2 4.36 Complete propagation 4 . 8 8 12 300 1 4 . 9 8 95.02 0.71 4.13 Completepropagation and 13 300 1 4.75 95.25 4 . 6 4 0 . 1 3 Nopropagation 4.75 14 300 1 4 . 2 7 95.73 4.17 0.21 Nopropagation 5.15 15 200 1 5.15 94.85 0.20 4 . 9 8 Complete propagation and 16 200 1 4.98 95.02 4 . 8 4 0.18 Nopropagation 4.98 17 25 1 5.40 94.60 5 . 4 0 0.00 No propagation 5.46 18 25 1 5.46 94.54 5 . 4 7 0.00 N o propagation and 19 25 1 5.56 94.44 0.12 5.46 Complete propagation 5 . 5 6
was contained in t h e t u b e x y of t h e pipette outside of t h e electric oven a n d did not burn. When thk methane in t h e mixture was dropped t o 3 . 7 j a n d 3 . j o per cent, no propagation was observed, although some methane was burned, as was shown b y t h e carbon dioxide found upon analysis. According t o these results, t h e low limit of complete propagation is between 3 . 7 j a n d 4.00 per cent when t h e initial temperature is j o o o C. a n d t h e initial pressure I atmosphere. At 400' C. a n d a t atmospheric pressure a mixture containing 4 , j j per cent methane completely propagated flame, as far as could be judged b y t h e eye, although 0 . 7 j per cent methane remained unburned. When t h e methane content was loyTered t o 4 . 4 7 per cent propagation could not be observed. T h e same was t r u e of mixtures containing 4 . 2 7 , 4 00, a n d 3 , ;j per cent methane. Experiments 17, 18 a n d 19 were performed t o obt a i n t h e low limit of complete propagation of methaneair mixtures under ordinary conditions of temperat u r e a n d pressure. This value lies, i t will be noted, between j . 4 6 a n d j . j 6 per cent methane. Vndoubtedly a small amount of carbon dioxide was formed in t h e case of Experiments 1 7 a n d 18, b u t not enough t o detect by t h e method of analysis used. I n each test a n analysis was made of t h e mixtures before a n d after sparking. T h e sum of t h e carbon dioxide a n d methane should equal t h e methane present before sparking. T h e analyses agreed quite well. A curve representing t h e results of t h e experiments is shown a t Fig. 2 . T h e variation of t h e limrts of explosibility with temperature a n d pressure may be explained on purely thermal grounds. If one heats a n expIosive mixture of methane a n d air, t h e number of collisions between t h e molecules increases with rising temperature a n d t h e speed of
Val. 7, NO. j
reaction increases until finally a violent reaction a n d appearance of flame follows. T h e temperature a t which this kind of a reaction takes place is called t h e ignition temperature. T h e ignition temperature of methane-air mixtures was f o u n d t o be between 6 5 0 ' a n d 7 5 0 ' C. by Dixon a n d Coward.' A slow combustion effect is possible, however, below t h e ignition temperature, depending on t h e nature, of t h e source of ignition a n d length of time t h e gas is heated. B u t in order t h a t flame may be propagated throughout t h e gas mixture, t h e heat of reaction of a layer of gas near t h e igniter must be sufficient a n d its r a t e rapid enough t o raise t h e temperature of t h e adjacent layer t o t h e ignition temperature. Obviously t h e higher t h e initial temperature t h e less heat will be required t o raise t h e temperature of a given mass of t h e gas t o t h e ignition temperature, a n d consequently t h e
TEUPER.IUIX
FIG.2-EFFECT
- oEa cim
INCREASING THE INITIAL TEMPERATURE O N THE Low LIMIT OF COMPLETE PROPAGATION OF FLAME IX METHANE-AIR MIXTURES OF
smaller is t h e heat of combustion a n d t h e percentage of methane required t o furnish this q u a n t i t y of heat. S L O W COMBUSTION O F N E T H A X E - A I R MIXTL-RES AT H I G H T E M P ERA T UR E S W I T H 0 UT S P A R K I S G
A few experiments were performed t o show t h e ext e n t of burning when various mixtures of methane a n d air were subjected t o high temperatures without sparking. TABLE 11- RESULT^ O F EXPOSURE O F METHANE-AIR MIXTURESTO HIGH TEMPERATURES WITHOUT SPARKING Temp. C. 500 500 500
Pressure Atmos. 1 1 1
---
Analysis before ignition Analysis after ignition -*_.
CHI 4.27 4.27 4.60
Air 95.73 95.73 95.40
CHI 4.21 3.89 3.74
CO? 0.10 0.40 0.90
Exposed Min. '/n 30 30
T h e results, given in Table 11, show t h a t no appreciable combustion effect occurred in experiments previously cited between t h e time t h e gas mixtures were introduced i n t o t h e pipette a n d t h e time t h e y were sparked. I n t h e experiments previously described, not longer t h a n z seconds was required for t h e mixtures t o a t t a i n t h e temperature of t h e oven after introduction into t h e exhausted pipette. It will be observed t h a t as much as one-half minute exposure t o a temperature of 500' C. resulted in only a small a m o u n t of carbon dioxide. E F F E C T O F I N C R E A S I N G T H E I N I T I A L P R E S S U R E ON T H E E X P L 0 S I B I L I T Y 0 F M E T H A N E AI R MI X T U R E S
-
Some experiments were made with t h e a p p a r a t u s shown in Fig. I t o determine t h e effect of initial presI H. B. Dixon and H. F. Coward, "The Ignition Temperature of Gases." Chem. News, 99 (March 19, 19091, 139.
T H E J O 1 7 R S a 1 L O F IA\-D17STRI.4L A S D E - V G I S E E R I S G C H E M I S T R Y
M a p , 191j
sures higher t h a n ordinary on t h e explosibility of methane-air mixtures. T h e first experiments were made with pressures u p t o five atmospheres, b y raising t h e level bottle of t h e a p p a r a t u s high enough t o p u t the gas under this pressure. It was found t h a t increased pressure u p t o five atmospheres h a d no effect in changing t h e low limit of complete propagation. I n other words, t h e value, a b o u t j . j o per cent methane. is t r u e a t five atmospheres pressure. S U 11 MIA RY
When t h e initial temperature of methane air mixtures is j o o " C., t h e low limit of complete propagation of flame of t h e mixtures is between 3 ;j a n d 4 . 0 0 per cent methane. As t h e initial temperature is lowered from j o o o C., t h e low limit is raised until a t ordinary temperatures i t is about j . j per cent methane. Differences in t h e initial temperature of as much as 200' C . higher, shift t h e low limit only from 5 . j o per cent t o between 4.98 a n d j . I j per cent methane. T h e results are i m p o r t a n t in t h a t t h e y show t h a t pressure a n d temperature conditions m a y vary over rather a wide range without affecting t h e explosibility of methane-air mixturef . Inconsistent results t h a t have been obtained i n t h e laboratory b y different investigators on t h e limits of inflammation of methaneair mixtures cannot be explained on t h e basis of slight variations in temperatures a n d pressures. T h e y are better charged t o t h e nature of t h e source of ignition, method of ignition, size a n d shape of t h e containing vessel, a n d in some cases, inaccuracies in mixing a n d analyzing the gases. Since t h e low limit of complete inflammation for methane-air mixtures is not changed at pressures as great as five atmospheres, i t can be s t a t e d t h a t even i n t h e deepest coal mines t h e low limit is not altered from t h e limit a t ordinary temperatures. CHEMICAL LABORATORY, BUREAUO F hlINES PITTSBWRGH
T H E VARIATION IN COMPOSITION OF NATURAL GAS FROM DIFFERENT SANDS IN THE SAME FIELD' , B y G A. BWRRELLAND G. G. OBERFELL Received December 15, 1914
I n working on t h e composition of n a t u r a l gases from different p a r t s of t h e country, t h e authors have found t h a t n a t u r a l gases from different sands in t h e same field m a y differ appreciably in composition. Invariably t h e gas f r o m t h e shallower sand has contained less of t h e heavier paraffin hydrocarbons t h a n t h a t from t h e deeper sands. T h e most striking variation yet encountered has h a d t o d o with n a t u r a l gases from t w o different sands in a gas field near Trafford C i t y , Westmoreland C o u n t y , P a . a n d not far from Pittsburgh. T h e compositions of these gases follow: GAS F R O M Murraysville sand Elizabeth sand Depth of s a n d . . . 1700 f t . 2295 f t . Rock pressure. .. . . 190 lbs. per sq. in. 1000 lbs. per sq. in. CONSTITUENTS C o t CHI h-2 COX CHI CzHe Percentages .... . . Trace 9 8 . 8 1 . 2 Trace 94.0 5.2 '
.
.
Nt 0.8
It will be noted t h a t f r o m t h e shallow s a n d there was collected a sample of almost pure methane, while in t h e deeper sand there is contained in addition t o 1
Published by permission of the Director of the Bureau of Mines.
419
methane a n appreciable proportion of t h e higher members of t h e paraffin series of hydrocarbons. If one were t o assume a common source of origin for t h e natural gases in t h e t w o sands, t h e n b y some process of separation t h e gas in t h e upper sand has been freed of i t s ethane a n d higher paraffins. I t should be added t h a t t h e paraffins were analyzed by burning t h e m in oxygen. not b y fractional distillation; hence in t h e case of t h e gas from t h e deep sand, only t h e t w o predominating paraffins are shown. Undoubtedly small proportions of propane, t h e butanes, etc., were also present, as in t h e case of other natural gases containing methane a n d ethane. CHEMICAL LABORATORY, BCREACO F MIXES PITTSBURGH
A SIMPLIFIED FERROUS SULFATE METHOD FOR THE DETERMINATION OF VANADIUM IN STEEL By GEORGET. DOUGHERTY Received October 17, 1914
I n t h e application of Johnson's' or similar methods for t h e determination of vanadium in steel, considerable difficulty is often experienced in producing a colorless or "old rose" shade with ferrous sulfate in t h e solution containing a n excess of permanganate after t h e ppeliminary oxidation of t h e 1-anadium. T o obviate this difficulty t h e following method has been developed. i n which this oxidation of t h e vanadium is effected by a sufficient q u a n t i t y of nitric acid alone or with a m monium persulfate. METHOD-Treat 2 t o 1 g. of t h e drillings in a j o o cc. Erlenmeyer flask, with 6 0 cc. of water a n d I O cc. concentrated sulfuric acid. After heating t h e solution nearly t o boiling. until t h e reaction is complete, a d d 40 cc. of nitric acid (sp. gr. 1.20) a n d boil thoroughly for I O minutes t o oxidize t h e iron a n d vanadium a n d t o expel t h e last traces of nitrous fumes. Cool t h e solution. a d d 6 0 cc. of cold sulfuric acid (I : z ) a n d dilute in a 600 cc. beaker t o 4 j o cc. Add 3 cc. of a freshly prepared I per cent solution of potassium ferricyanide, a n d t i t r a t e rather rapidly, with constant stirring, with 0.05 N ferrous ammonium sulfate, t o t h e appearance of t h e first d a r k blue color. T h e e n d point can best be observed b y looking through t h e side of t h e beaker t o w a r d t h e b o t t o m of t h e beaker placed directly before a window. Deduction of a blank of 0.4 cc. of t h e ferrous solution has been found necessary, a n d is independent of t h e weight of t h e sample, t h e presence of chromium, a n d of t h e carbon content u p t o 0.j per cent C . F o r steels with over 0.50 per cent C, t h e blanks are higher; a n d , moreover! with 4 g. samples of such steels, t h e e n d point is rendered indistinct b y a turbidity which appears toward t h e end of t h e titration. This difficulty m a y be avoided b y adding t o t h e solution immediately after t h e boiling with nitric acid as above, 60 CC. of I : P sulfuric acid a n d j t o 8 g. of ammonium persulfate (which i n t h e absence of silver nitrate will not oxidize t h e C r a n d M n ) , a n d continuing t o boil for I j minutes, so t h a t all nitrous oxides a n d hydrogen peroxide are expelled. (Before this second boiling, wash down with h o t water loose specks of t h e per1
C. M. Johnson, "Analysis of Special Steels."
