T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
3 74
but as the half-life period of the radium emanation is 4.8 days and t h a t of t h e thorium emanation 54 seconds, the latter is very rapidly and the former very slowly reformed. Hence any active gas which is found in the solution after t h e ten minutes' boiling and during the progress of the experiment can be considered as thorium and not radium emanation. The flask ,4 is now connected with B and gently boiled while a constant current of air is drawn through the whole apparatus in t h e direction of the electroscope. This current can be controlled b y t h e needle valve. C assists in regulating t h e pressure in the apparatus. If t h e boiling is steady t h e leaf does not vibrate and readings are readily made. If the air is pulled too rapidly through t h e apparatus, the emanation is too much diluted; if too slowly, a considerable portion of the emanation decays before it reaches t h e electroscope. A maximum effect can therefore only be obtained b y trial. The activity of any given soil is, of course, the sum of t h e activities of the acid and alkaline solutions obtained from t h a t soil. The natural leak of the electroscope under the experimental conditions is obtained by substituting for A , a similar flask containing distilled water and boiling as already described. I t was noted t h a t if air was
A
-A-
FIG.I
passed over calcium chloride and phosphorus pentoxide and then through t h e electroscope, t h e leak was smaller t h a n when no air was passed. Also, if the leaf was steady and air was then passed, the leaf slowly rose during a period of ten minutes and usually over about five small scale divisions. This result is probably closely connected with t h e observations made by Schlundt and Moore' in a somewhat similar case; and discussed by Randall2 in a later paper. Readings were made only after the maximum point was reached. The electroscope was standardized by using an acid solution of a thorium mineral in which the disintegration products are in equilibrium. I n t h e present case an analyzed specimen of thorianite was used. A flask containing distilled water, t o which a certain volume of t h e standard thorianite solution was added, was substituted for A after first boiling t o get rid of the radium emanation. The effect on t h e electroscope of t h e emanation from a known quantity of thorium 1 2
Trans. A m . Electrochem. Soc.. 8 (1905), 292. I b i d . , 2 1 (1912). 463.
Vol. 6 , N o .
j
could therefore be observed and compared with the results obtained from the soil solutions under similar conditions after the leak was deducted in each case. In order to test the accuracy of the method, different thorianite solutions of known strength were used and the results compared. For example, I O cc. containing 0.0021 gram thorium metal gave (leak deducted) a drop of twelve divisions per hour. 40 cc. of the same solutions gave a drop of 47.8 divisions per hour. The results obtained are shown in Table 111. TABLEI11 Depth Durham sandy l o a m . . . . . . . . , . . . . . Norfolk sandy loam. . . . . . . . . . . . . . Decatur clay l o a m . . , . . . . . . . . , , . . . Hagerstown l o a m . , , . , . . , . , . . , . . . York silt l o a m . . . . . , , , . . . , . . . . . . .
10"-36"
0'1-14" 4"-36" 8 "-36fi 0"-8"
Thorium gram X 10-5 per gram of soil ,
5.4 3.3 5.6 4.02 4.3;
The results are not numerous enough t o justify any conclusions as regards t h e relative amounts of thorium in the soils and subsoils. Comparing them with Joly's results on rocks, they seem t o indicate t h a t soils contain more thorium than most rocks, t h e average of the above results being much higher t h a n the average of Joly's results, Z J ~ Z . , 1.58 X 10-j gram per gram of rock. T h e figures are also higher than those obtained b y Blanc for Roman soils.' Strutt2 has shown t h a t the amount of radium in the earth's crust is more than sufficient t o account for its internal heat. He did not take into account the thorium present. Averaging the amount of radium in the soils and subsoils and reducing this back to the uranium content, it can readily be seen t h a t the amount of uranium present is about I O per cent t h a t of the thorium. TTrhile it is difficult t o state just to what extent t h e thorium assists in maintaining the earth's internal heat, the effect must a t least be appreciable. The small variation in the amount of thorium in the five samples tested is noteworthy. hly thanks are due t o Dr. Frank K. Cameron, Chief of the Division of Physical and Chemical Investigations, Bureau of Soils, for many courtesies extended during the progress of this investigation. BUREAUOF SOILS
WASIIISGTON, D . C.
PARTIAL AND INTERMITTENT COMBUSTION OF GAS By E. E. SOMERMEIER Received November 21, 1913
C 0 M B U S T I B I. E , I K F L A M 31A B L E A S D E X P L 0 SI V E MIXTURES
X combustible
m i x t u r e is usually defined as a mixture of a composition such t h a t if any part of i t is raised t o its ignition temperature a reaction between t h e component3 will become self-sustaining and will extend t o all parts of t h e mixture; an iizflammable m i x t u r e as a mixture of a composition such t h a t if i t is ignited a t any point a visible flame will spread throughout t h e entire mixture; a n explosive m i x t u r e as a mixture of a composition such t h a t if a portion of it is raised t o its ignition temperature an explosive reaction will 1
2
Phil. Mag., 18 (1909). 146-148. Proc. Roy. Soc., ( A ) 17 (1906), 472-485.
T H E J O U R N A L OF I N D U S T R I A L A N D EiVGINEERING C H E M I S T R Y
May, 1914
take place throughout t h e entire mass. Given a sufficiently large volume of gas any mixture which is combustible or inflammable is also explosive. With t h e combustion once started a n y one of three things is possible: The reaction may decrease in rapidity; i t may remain constant; or it may increase in rapidity. -4n exactly constant rate of reaction is so rare t h a t i t may be disregarded as a possibility and t h e reaction may be expected either t o accelerate or t o decrease in velocity. If it accelerates an explosion will occur, provided a sufficiently large volume of gas is present. If it decreases, t h e combustion mill die out and t h e gas, practically speaking. will be incombustible or at least only partially combustible. DATA
ON
THE
COMPOSITION
OF
COhIBUSTIBLE
AXD
EXPLOSIVE MIXTURES
The d a t a in t h e literature regarding t h e lon7er limits of combustible and explosive mixtures of gas with air or with oxygen differ greatly. As an illustration, Hempell gives t h e lower limit of combustible mixtures of hydrogen with air as from j t o 6 per cent. 1Iost other authorities give from g t o I O per cent. Techlu2 gives t h e lower limits of an explosive mixture ofmethane with air as 3.2 per cent. Burrel13 gives j . j per cent. Most other authorities give about 6.0 per cent. I n comparing such widely different values one is a t a loss as t o the real facts. T h a t differences of such magnitude are due t o errors of manipulations on t h e part of some of t h e experimenters is hardly probable a n d they are rather t o be ascribed t o differences in conditions and in methods of work. Some of the more probable factors contributing t o these differences in experimental results are: ( I ) Impurities in the gases with which t h e experiments were performed. ( 2 ) Differences in t h e initial temperature of the gas. (3) Differences in the initial pressure of the gas. (4) Differences in t h e volumes of gas used. (j) Differences in method of ignition. (6) Differences in t h e design or style of the containers. The recorded results, unless otherwise noted, were presumably obtained by starting a t ordinary laboratory temperature and a t atmospheric pressure, and it is hardly possible t h a t any large amounts of unknown impurities were present in the gas mixtures used. It would therefore appear t h a t no great discrepancies in results are t o be explained by any or all of the first three sources of error, and large variations are more probably t o be explained as due t o t h e latter three. By varying these conditions t h e writer, as will be shown later in this paper, obtained results, which, while they are not entirely concordant, do tend t o suggest reasons for t h e different values given for combustible a n d explosive mixtures. E X P E R I U E X T S TO T E S T T H E I K F L U E N C E
O F VOLUME OF
GAS, METHOD O F I G X I T I O N A N D S T Y L E O F CONTAINER
I n t h e experiments described in this paper the following volumes of gas mixtures were used: “Gas Analysis,” Hempel. J puakl. Chem , 75 (1907). 212. a THISJOURNAL, 6 (1913), 181. 1
COSTAISER
Dimensions Diam. No. Cm. 1. . . . . . . .. 8 2....... 3 . ,, . , . . 9.5 4 . . . . . . . 20 5 . . . . . . 30
Length Cm.
.. 26 29 38 42
Kind Glass flask Iron cylinder Glass cylinder Iron cylinder Iron cylinder
T’ol. cc. 145 1,300 2,100 13,000 30,000
Condition of experiment Gas confined Gas confined Open a t end Gas confined Gas confined
DIMENSIONS OF T H E CONTAISERS-For the smallest container an ordinary short-neck globular COZ flask was used. This flask when stoppered had a capacity of 1 4 j cc.
Each of the iron cylinders was fitted i\-ith an opening for t h e attachment of a water-sealed glass tube, with a n opening for the insertion of a stopper carrying copper lead wires t o m-hich t h e wire fuses were attached and with two pet cocks or openings through which gas could be admitted or withdrawn and also through which water could be admitted t o replace t h e gas withdrawn in sampling. The accompanying cut of the 13,000 cc. cylinder shows the general arrangement of the stirring apparatus, glass delivery tube, paraffined paper-top, etc. The
projecting flange a t the top is of galvanized iron and was used when i t was desired t o secure a water seal around paraffined paper. I n experiments with mixtures rich enough t o produce much of a reaction several thicknesses of paraffined paper were used and t h e necessary weight t o hold t h e paper in place secured by using the ring above the paper as t h e fulcrum of a lever j or 6 feet long, upon t h e end of which weights were placed. I n this way pressures equivalent t o j o o or 800 pounds upon the head of t h e cylinder were readily secured. The following methods of ignition were used:
316
s
1 2 3 4 5 6
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
0 . 5 t o 0.75 cm. No. 34 platinum wire, heated t o white heat. 0 5 a n d 5 cm. No. 34 platinum wire, fused. 0 5 and 5 cm. A-0, 34 iron wire, fused. 5 cm. k'o. 34 tantalum wire, fused. 0 25 cm spark from induction coil Oxygen-natural gas flame
I n performing t h e experiments with closed containers, two methods of observing whether or not a reaction took place were used. (I) A bent glass tube was attached t o t h e container, t h e open end of which dipped into water. With a vigorous reaction, gas was forced through t h e tube and bubbled up through the water. With a less vigorous reaction, t h e water in the tube was depressed through a noticeable distance. 145 cc flask 1,300 cc cylinder
DIAMETERSOF DELIVERYTUBESUSED 3 mm tube 13,000 cc cylinder 6 mm tube 30,000 cc cylinder
12 mm tube 12 mm tube
( 2 ) The mouth of the container was closed with paraffined paper, which, being flexible, was visibly moved b y a slight reaction in the gas mixture, while with a vigorous explosion or combustion it was ruptured. This method was employed in some of t h e experiments with t h e cylinders of capacities of 1300 cc. and 13,000cc. I n t h e experiments in which a delivery tube was used, any gas which escaped was replaced b y water, and t h e analysis of t h e residual gas did not need t o be corrected for dilution with air. The composition of t h e residual gas from experiments in which t h e cylinders were closed with paraffined paper was usually somewhat affected b y dilution with air. There was more or less leakage of gas outward around t h e edge of t h e cylinder when t h e gas was subject t o t h e pressure caused b y combustion or explosion, and this was followed b y a resultant leakage of air inward upon t h e cooling and contraction of t h e gas. T h e errors in t h e results caused b y this leakage were, however, of minor importance a n d had no bearing on t h e general conclusions deduced from t h e analysis. I n using t h e 145 cc. flask no effort was made t o mix t h e gas and air, as with this small volume diffusion was deemed sufficient t o give a uniform mixture after a few minutes. I n using cylinders containing 1300 cc., 2 0 0 0 cc., and 30,000 cc., mixing was secured by inverting t h e cylinder t e n or twelve times and allowing i t t o stand each time for a few seconds up t o several minutes before reversing. I n using a cylinder of 13,000 cc., mixing was accomplished by means of a pair of fan blades on a rotating shaft which was turned several hundred times before t h e ignition of t h e mixture. The current used for heating the 0.5 t o 0.75 cm. of No. 3 4 platinum wire t o a white heat was obtained b y using two 3 2 candle power carbon lamps in parallel. For fusing t h e platinum, iron and tantalum wires, three t o four 3 2 candle power lamps in parallel were used. I n t h e fusing of t h e platinum wire less t h a n one calorie of heat was developed. I n t h e fusion of t h e iron and tantalum wires slightly more heat may have been developed owing t o some oxidation. I n t h e experiments with t h e 13,000 cc. cylinder one calorie of heat would be sufficient t o raise t h e temperature of t h e gas mixture only about 3' C .
v01. 6 , NO.
j
All t h e experiments were performed a t laboratory temperatures which varied for different days from as low as 18" C. t o as high as 27' C. Some of t h e results obtained with t h e different methods of ignition and t h e different volumes of gas together with analyses of t h e resultant gases are as follows: HYDROGEN AND AIR
145 Cc. FLASK-Method of ignition, 0.5 cm. No. 34 platinum wire heated t o white heat for 2 seconds. A blank on air under the same conditions gave a 5 cm. depression of water in the delivery tube. WITH THE
RESULTS WITH DIFFERENTPERCENTAGES OF HYDROGEN I N AIR Per cent hydrogen
Depression Cm.
Per cent hydrogen
10 15 20
6.0 7.1 8.2
4.5 5.0 5.5
Depression Cm. 20 70 Flask blown-off oi the stopper.
Turning on the current for two additional intervals of one second each gave further reactions as follows: Per cent hydrogen
Depressions Cm.
Per cent hydrogm
5.0 5.5
15 and 10 20 and 10
6.0 7.1
Depressions Cm. 20 and 12 20 and 15
After the third ignition of the 5.5 per cent mixture, analysis of residual gas for oxygen showed t h a t only 0.2 per cent of the oxygen had burned, equivalent t o 0.4 per cent of hydrogen. RESULTSWITH Per cent hydrogen
A
0.25 CM.SPARK FOR 0.5 SEC.FROM A N INDUCTION COIL Per cent Depression Depression hydrogen Cm. Cm.
4.3 1st s p a r k . , . . . . . . 20 2nd s p a r k . . . . . . . 20 3rd spark.. . . . . . . 5
5.6 1st s p a r k . . . . . . . 25 2nd s p a r k . . . . . . . 25 7.0 1st s p a r k . . . . . . . 75 2nd s p a r k . . . . . . . 50
WITH THE 1300cc. CYLINDER-Method of ignition, fusion of 0.75 cm. of No. 34 iron wire. Extent of reaction noted by movement of paraffined paper on the head of the cylinder. 1
__
Per cent hydrogen 4.5 4.6 5.0 6.0
Result No visible reaction Very faint reaction F a i r reaction F a i r reaction
Per cent hydrogen 7 8 9 10
Result Very fair reaction Weak explosion Fair explosion, not violent Vigorous explosion
WITH THE CYLINDER WATER-SEALED, glass tube t o allow the escape of gas, and a n iron wire fuse, several experiments with 7 . 7 per cent hydrogen all gave vigorous reactions, gas being forced out through the water-seal. Analysis of the residual gas for oxygen showed that from 1.4 t o z per cent of hydrogen had burned. WITH THE 13,000 cc. CYLINDER, iron wire fuse and 6 per cent hydrogen, about 500 cc. of the gas were forced out through 20 cm. of water. An analysis of the residual gas for oxygen showed t h a t about 0.5 per cent of hydrogen had burned. With 7 . 7 per cent hydrogen about z liters of gas were forced out of the cylinder. An analysis of the residual gas showed t h a t 0.4 per cent hydrogen had burned. Ignition of the residual gas by means of additional fuses gave combustion reactions up t o I O fuses. Up t o the fourth fuse the reaction produced forced gas out of the cylinder through 30 cm. of water. Using 0.5 cm. of No. 34 platinum wire heated to a white heat for two seconds, a 7 . 7 per cent mixture of hydrogen gave two distinct reactions, the gas escaping through 20 cm. of water in two closely succeeding but distinctly separate portions. Analysis of the residual gas showed that 1.6 per cent of hydrogen had burned
T H E J O U R N A L O F I N D C S T K I A L -4 -VD E ATGI N E E RI N G C H E M I S T K Y
LIay, 1914
Using a spark from the induction coil for about 0.1second, a 7.7 per cent mixture of hydrogen gave a very vigorous reaction, several liters of gas being forced out of the cylinders. Analysis of the residual gas indicated t h a t 0.8 per cent of hydrogen had burned. With 7 . 6 per cent hydrogen and with the spark left running for several seconds, three distinct reactions were observed. WITH THE 30,000 cc. CYLINDER and iron wire fuse, mixtures of from 7.3 t o 7.7 per cent hydrogen gave fair reactions as was indicated by the forcing of gas out of t h e cylinder through water. Analysis of the residual gas showed that only about 0.4 per cent of hydrogen had burned. A 7.7 per cent mixture ignited with a dozen successive fuses gave reactions each time; up to the ninth fuse, the reaction forced gas out of the cylinder through 18 cm. of water; whereas, the burning of a fuse in the cylinder filled with air gave no visible depression., NATURAL GAS AND AIR
Natural gas from the Columbus, Ohio, city mains was used. This gas on analysis was found to consist of approximately 85 per cent of methane and 15 per cent of ethane. WITH THE 145 cc. FLASK, a 5 per cent mixture of natural gas and air gave no visible reaction when ignited with 0.75 cm. of No. 34 platinum wire heated t o a white heat Per cent natural Time of Depresgas spark sion in air Spark Seconds Cm.
4.4
5.0
1st 2nd 3rd 1st 2nd
1 1 1 1
1
30 20 20 30 25
Per cent natural gas in air 5.6
Blank on air
Time of Depresspark sion Spark Seconds Cm. 1st 2nd 3rd 4th 1st 2nd
112
2 2 4
1 5
75 60 50 75 10 20
On several other tests with mixtures containing from 5.7 per cent to 5 . 2 per cent of gas and using a spark for 0.5 second, the flask was blown from the stopper. WITH THE 1300 cc. CYLINDER-Method of ignition, fusion of from 0.5 t o 0.75 cm. No. 34 platinum or iron wire. A 4.6 per cent mixture of gas and air produced a 4 cm. depression. A blank on air produced a depression of I cm. A mixture of 4.8 per cent of gas and air produced vigorous reactions, gas being forced out against a pressure of 5 lbs. per square inch. Analysis showed the presence of 2.6 per cent COZ. indicating t h a t about one-half of the gas had been burned. With paraffined paper closing one end of the cylinder, and with a 0.75 cm. platinum wire heated t o fusion, a fair reaction was detected with as low as 4.6 t o 4.7 per cent mixtures of natural gas and air. Mixtures of from 4.9 t o 5 per cent of gas and air gave fair combustion, a distinct flame being visible. RESULTS WITH 5 CnI. KO, 34 IRON AND PLATINUM FusEs-Blanks on fuses in air gave for the iron fuse a depression of 12 cm. and for the platinum fuse a depression of IO cm. A 4.3 per cent mixture of gas and air gave a depression of 30 cm. with a n iron fuse and a depression of 20 cm. with a platinum fuse. Using a 5 cm. tantalum wire fuse, blanks on fuse in air gave a depression of 12 cm. Mixtures of 4.3 per cent and 4.4 per cent of gas and air gave depressions of 40 and 50 cm., respectively. WITH THE 13,000 cc. CYLINDER, iron wire fuse, paraffined paper head on cylinder. With a 4.7 per cent mixture of natural gas, no visible reaction was produced. With a 4.8 per cent mixture of natural gas, a faint reaction was produced. With a 5 per cent mixture of natural gas, a fair reaction was produced. With a 5 . 2 t o 5 . 3 per cent mixture of natural gas, a fair reaction was produced, the paper head of the cylinder being scorched by the heat of the combustion.
.
377
Tests after combustion on the residual gas from mixtures containing 5.2 and 5.3 per cent of natural gas gave results for C02 of from 0.8 t o 1.2 per cent, indicating that approximately this amount of the natural gas had burned. These values are, however, somewhat too low, owing to the leaks inward of air after combustion. This is shown by the more complete analysis after combustion of the residual gas from a 5 per cent mixture of natural gas, upon which values were obtained as follows: COz 1.4, CHI 2.7, C2H6 0.6 per cent. On the basis of natural gas consisting of approximately 85 per cent CHI and 15 per cent C2H6 the original mixture contained 4.25 per cent of CHI and 0.75 per cent of C2H6. On the residual gas after combustion the CzHs is 0.15 per cent lower and the CHI 1.55 per cent lower than in the original mixture. If these amounts burned to COZ the COZ formed would equal 1.55 0.30 = 1.85 per cent as against 1.4 per cent of CO:! actually found. This corresponds t o a dilution of the original mixture with approximately 25 per cent of air.
+
EFFECT O i IGNITION BY A WHITE HOT PLATINUM WIRE COMPARED WITH IGNITION BY FUSION O F THE WIRE
A 5.1 per cent mixture with 0.75 cm. No. 34 platinum wire heated to a white heat for two seconds gave no visible reaction, but upon turning on additional current and fusing the wire, a fair reaction occurred, about 500 cc. of gas being forced out. of the cylinder. Analysis of the residual gas for carbon dioxide and oxygen indicated that only about 0.2 per cent of the natural gas had burned. The ignition of the gas by fusion of the wire and its failure to ignite from the wire raised t o a white heat shows very clearly the great effect of a very high temperature of ignition upon the starting of the reaction. EXPERIMENTS
TVITH THE OXYGEN-XATURAL
GAS FLAME
AS
A
SOURCE O F IGNITION
hlixtures of natural gas and air, and hydrogen and air were collected over water in the 2100 cc. glass cylinder which was then closed with a glass plate. The gases were mixed by inverting the cylinder a number of times, and then with the cylinder inverted, it was quickly slipped off of the glass plate which closed it and passed over the oxygen gas flame, the flame being in the cylinder for about one-half second. This flame was about I O cm. long and consumed about 3 cc. of natural gas per second. With natural gas no visible combustion was obtained with j per cent of gas, but with a 5.5 per cent mixture the combustion was' quite evident, a blue flame spreading slowly throughout the cylinder. With hydrogen no reaction was detected with a 6 per cent mixture. TS'ith a 7 per cent and a 7.7 per cent mixture no visible flame was noticeable but an appreciable reaction was indicated by the deposit of a film of moisture upon the cold sides of the cylinder. That an apprcciable reaction is started by the oxygen-natural gas flame in mixtures of natural gas and air lower than 5 . 5 ,per cent is shown by the following experiments upon different mixtures of gas and air in the 13,000 cc. cylinder: I n making the cxperiments a cork was removed from a 2 cm. opening in the side of the cylinder and the tip of the flame inserted into the cylinder for from I to 3 seconds. Considerable reaction occurred as was shown by the rapid swelling of the paraffined paper top used to close the cylinder and by the rapid escape of gas through the opening in which the flame was inserted. In each case the effect was greater than t h a t which was produced in blank tests upon the cylinder filled with air. But in the mixtures used no violent reaction occurred. The extent of the reaction was approximately determined by analysis of the residual mixtures for CO2. The flame used 3 cc. of natural gas, and produced approximately . 3 cc. of COz per second; or in the 13,000 cc. mixture less than 0.03 per cent of COz per second was added from this source. The results obtained upon the residual mixtures were 'as follows :
T H E J O U R L V A L O F I - V D l - S T R I A L A N D ELVGINEERING C H E M I S T R Y
3 78 Per cent of natural gas in mixture 4.4 4.0 3.2 2.0
Time of flame in cylinder Seconds
5 5 3 4
Per cent COP in resultant mixture 1.0 1.0 0.6 0.3
ApproxiPer cent of m a t e cc. of COn from Con f r o m natural gas flame gas burned burned 0.15 0.83 100 0.15 0.83 100 0.10 0.50 60 0.10 0.20 25
These results all show appreciable combustion around the flame. This combustion was in all cases greater than is shown by these results on account of the expansion of the gas and the dilution of the remaining gas with air upon contraction before the gas was sampled and analyzed. That partial combustion of such mixtures occurs is shown by the well known lengthening of a lamp flame in air containing fire damp. ANALYSIS O F RESULTS
The experiments here recorded show conclusively t h a t with a high initial ignition temperature a reaction may start in a gas mixture, which, as a whole, may be incombustible because the heat of combustion is not sufficient t o maintain t h e temperature a t t h e kindling point. Hence all of t h e mixture will not burn although t h e reaction may be sufficiently extensive as t o make the mixture appear t o be combustible or explosive. With the source of high temperature employed t o cause ignition acting for only a very brief interval of time, as during t h e fusion of platinum or iron wire, t h e resultant reaction quickly ceases but not until a combustion of gas has occurred, the heat of which is in some cases equivalent t o hundreds of time the energy required t o heat the platinum or iron fuse. The heat liberated b y t h e fusion of 0.75 cm. of N o . 34 platinum or iron wire is only a fraction of a calorie. I n a 7.7 per cent mixture of hydrogen this fuse, as has been shown, causes a combustion of 0.4 per cent of hydrogen i n a 30,000 cc. mixture or of 1 2 0 cc. of hydrogen. This liberates about 300 calories of heat. I n the smaller containers a greater percentage of t h e hydrogen was burned. For example, in t h e 1300 cc. cylinder as high as 2 per cent of hydrogen burned or only 2 6 cc. From this i t would appear t h a t when t h e combustion is started from a source of very high temperature, more gas is burned in a large volume of mixture t h a n in a small volume, b u t t h a t t h e greater percentage of t h e gas is burned in t h e smaller mixture. This is a t least partially accounted for by t h e cooling of t h e gas b y the walls of t h e container, especially where small volumes are burned; b u t with large volumes of gas, as in t h e case of t h e two large cylinders holding 13,000 and 30,000 cc., respectively, this would be of little effect, and in a room full of gas the effect would be entirely negligible. With a continuous source of high temperature, as with a white hot wire, a lamp flame or a running electric spark, t h e reaction produced may be intermittent. The gas immediately around t h e point of ignition burns and expands, and combustion around t h a t point ceases until another portion of the mixture of gas and air has replaced t h e expanded gas and products of combustion, whereupon another reaction takes place resulting in a series of combustions or explosions. T h e limits of appreciable ignition or combustion of hydrogen and of natural gas in air vary with the volume of gas used, t h e source of ignition and the style
Vol. 6, NO. 5
of t h e container. I n a 2 0 0 0 cc. open cylinder t h e lower limit obtained for natural gas is about j . j per cent. With hydrogen t h e lower limit for very appreciable ignition was above 7 per cent. I n a closed container t h e lower limit for natural gas using 0.; cm. of No. 34 platinum wire heated white hot, was over j per cent. With a 0 . j cm. platinum or iron wire fused t h e lower limit obtained was 4.7 t o 4.8 per cent. With a j cm. No. 34 wire fused the lower limit obtained mas about 4.3 per cent. With a j cm. No. 36 tantalum wire fused t h e lower limit was about 4.3 per cent. With a 0 . 2 ; cm. spark from an induction coil the lower limit of appreciable reaction was about 4.3 per cent. With closed containers, 6 t o 7 per cent mixtures of hydrogen and air gave vigorous reactions with 0.5 cm. platinum or iron wire fuses. With t h e electric spark, mixtures as low as j per cent gave very noticeable reactions, and faint reactions were obtained with mixtures as low as 4.3 t o 4.6 per cent. For t h e same percentage of gas and t h e same method of ignition, small volumes of gas gave more vigorous reactions t h a n large volumes, b u t in total amount of gas burned, the combustion obtained in large volumes was greater t h a n t h a t obtained in small volumes. With smaller containers, or with a more powerful spark, or a longer wire fuse, undoubtedly very appreciable reactions can be obtained with mixtures of lower percentages t h a n those given, b u t with ordinary sources of ignition, large volumes of gas will not react appreciably unless t h e mixture is richer in gas t h a n t h e lowest limits obtained in these experiments. However, t h e thermal calculations' based on 850' and 700' as the ignition temperature required for explosive mixtures of natural gas and of hydrogen with air indicate t h a t mixtures of natural gas in excess of 2 per cent and of hydrogen in excess of 5.9 per cent are potentially explosive if conditions favorable t o t h e readtion are present. Some of these conditions, in addition t o a vigorous source of ignition, are unusually high in initial temperature of t h e mixtures of gas and air, presence of fine combustible dust, and an increase in t h e pressure of t h e mixture. The results of these experiments indicate t h a t a comparatively small excess of hydrogen above t h e theoretical requirement is necessary t o produce a vigorous reaction. Natural gas or methane, on t h e other hand, ignites with such difficulty t h a t , with ordinary methods of ignition, an appreciable reaction does not occur unless a very large excess of gas is present above t h a t required by the thermal calculation. DEPARTMENT OF METALLURGY OHIOSTATE UXIVERSITY COLUMBUS
DISTILLATIONLUNDER
WOOD DIMINISHED PRESSURE A CONTRIBUTION TO T H E PROBLEM OF UTILIZATION OF WOOD WASTE By MAXWELL ADAMSA N D CHARLESHILTON Received Dec. 27, 1913
The rapid decrease in the supply of long leaf pine available for t h e production of turpentine and t h e immense waste of resinous wood in t h e lumber indus1 THISJOURNAL,
6, 191.
