INDUSTRIAL A N D ENGINEERING CHEMISTRY
December, 1928
cent. Lead recoveries of 84 per cent have been secured. The results obtained experimentally are s h o r n in the accomDanying - - - table. Properties of Soapy Layer
The soapy layer contains sodium carbonate, caustic soda, and organic compounds of the type RONa. The gravities
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of the samples obtained varied from 35" to 38" Be. The material is miscible with water in all proportions and somewhat soluble in commercial gasolines. Other properties of the soapy material are being investigated. Considerable amounts of caustic were converted to carbonates and varying amounts were lost in the tar layer as well as in the mass of crystals.
Ignition of Mixtures of Air with Natural Gas and w i t h Methane by Induction Coil Sparks' E. G. Meiter PITTSBUROH
EXPERIMENT STATION,
u. s. BUREAUOF
A
KNOWLEDGE of the relative inflammabilities of various mixtures of air with Pittsburgh natural gas and with methane is important, because the United States Bureau of Nines uses natural gas rather than methane for producing explosive atmospheres for its investigations of the safety of mining equipment and of explosives, and for explosion tests in its experimental mine. Natural gas is preferred because i t is available in large quantities and methane is not. Purpose of Investigation
Owing to the high methane content of the natural gas used in the Pittsburgh district it has been customary to assume that its flame properties are similar to those of methane. It is known2 that the ignition temperature of natural gas, as determined in a quartz tube, is somewhat lower than that of methane. This evidence is not, however, conclusive as regards the propriety of the use of natural gas in testing the safety of mine electrical equipment. The purpose of the tests described in this paper was therefore t o determine this relation under constant experimental conditions when an electric spark is the igniting agent. A careful comparison of the ignitibility of natural gas and methane under the same experimental conditions was therefore made.
Received July 16, 1928. Published by permission of the Director, (Not subject to copyright.) * Coward, Jones, Dunkle, and Hess, Carncgie Inst. Tech., Bnll. SO (1926). * J. Chcm. SOC.109, 523 (1916). 1 Ibid., 117,903 (1920). 8 U.S. Bur. Mines, Bull. 16, 63 (1912). 1
U.S. Bureau of Mines.
PA.
used, and therefore, in the present research, the same apparatus was used throughout for determining the relative igniting currents for mixtures of air with methane and with natural gas. Storage and Analysis of Gases
All gases and mixtures of gases were prepared and stored in glass gas-holders over mixtures of glycerol and water. The analyses of all hydrocarbon-air mixtures were made over mercury in a Bone and Wheeler6 apparatus having an accuracy of about 0.02 per cent. Composition of Gases Used
~ T E T H S S E - T ~methane ~ was obtained from a me11 whose gas contained less than 2 per cent impurity. It was purified by liquefaction and fractional distillation. The product contained no other hydrocarbons according to combustion analyses on the Bone and Wheeler apparatus. N-~TURAL GAS-A large sample of the natural gas used a t the Pittsburgh Experiment Station was drawn from the gas mains and stored over glycerol and water. An analysis of this gas by W. P. Yant and F. E. Frey, of the Bureau of hiines, gave the following: CH,, 88.9; C2He,7.4; CaHs, 2.4; C&, 0.8; higher hydrocarbons, 0.1; and nitrogen, 0.4 per cent.
Previous Investigations
Sastry3 and Wheeler4 have determined the relative ignitibility of a series of methane-air mixtures by measuring the current that had t o be broken in the primary circuit of an induction coil to give a t the spark gap in the ignition vessel a secondary discharge just capable of igniting the mixture. Wheeler found that the most easily ignitible mixtures of methane and air are those which contain about 8.3 per cent methane. Burrel16 a t Pittsburgh found by other methods that the most sensitive mixture of natural gas and air contained between 8.5 and 9 per cent gas. A direct comparison between the ignitibility of methane and natural gas cannot be drawn from these experiments. The igniting currents as determined by the method of Sastry and Wheeler are not absolute measures of the energy required to cause ignition. They depend upon the apparatus
MINES,PITTSBURGH,
Experimental
The apparatus 'and method of experimentation were similar to those described by Sastry3 and Wheeler.4 The measure of the ignitibility of n given mixture was the amount of electric current that had to be broken in the primary circuit of the induction coil to give a t the spark gap in the ignition vessel a secondary discharge just capable of igniting the mixture. APPARATUS-The apparatus used was the same as that previously described by Coward and Meiter.' (Figure 1) The ignition vessel was made of glass, with electrodes of bluntly pointed platinum wire. The one electrode was mounted on a micrometer head, graduated to 0.01 mm., so that the width of the spark gap could be accurately adjusted. The second electrode was fixed in position. For the present experiments a spark gap of 1 mm. was used. The volume of the ignition vessel was about 38 cc. A 15-em. (6-inch) induction coil was used with a motor-driven mechanical break in the primary circuit, similar to that described by Wheeler.8 0
7 8
Grice and Payman, Fuel Science Practice, 3, 236 (1924). J . Am. Chem. SOC.,49,396 (1927). J. Chem. SOC.111, 132 (1917).
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I N D UXTRIAL A N D ENGINEERING CHEMIXTRY
The current was supplied f r o m a 6-volt storage cell, regulated by a resistance and measured by an amm e t e r . Figure 2 is the wiring diagram. hfETHOD O B E X PERIMENTATION-The i g n i t i o n vessel was evacuated and a given g a s m i x t u r e introduced. The current in the primary circuit of the induction coil was then adjusted to an arbitrary value, and 200 sparks were passed through the explosive mixture a t the rate of about 1 per second. If ignition did not occur, a fresh sample of the gas mixture was introduced, the primary current increased 0.025 ampere, and sparks again passed. By following this procedure a value for the primary was eventuallv found which would Figure 1-Apparatus ignite the mixiure within the first few sparks, while a current of 0.025 ampere less in value would not ignite the mixture, however many sparks were passed. I n experiments with weak explosive mixtures which required much higher currents for ignition, the primary current was varied in steps of 0.05 instead of 0.025 ampere. At times anomalous results were obtained similar t o those experienced by Sastry3 and Wheeler.4 This irregularity was corrected by a careful cleaning of the electrodes and the ignition vessel; normal igniting currents were then observed.
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Vol. 20, No. 12
igniting currents” for the series of hydrocarbons-methane, ethane, propane, and butane. He found that the igniting current for the most readily ignited mixture was greater for methane than for any other paraffin hydrocarbon gas. As natural gas is a mixture of these hydrocarbons, i t may therefore be expected to have a lower igniting current than methane, and the two sets of experiments are thus in qualitative agreement. Table I-Relative ~-ATURAL
GAS Per cent 5.95 6.08 6.25 6.41 6.68 6.92 7.05 7.30 7.62 8.04 8.28 8.53
Igniting Current for Natural Gas-Air and Methane-Air Mixtures RELATIVE~ G N I T I N G RELATIVEIGNITING CURRENT METHANE CURRENT Amperes Per cent Aniberes 1.85 6.20 1.75 1.50 6.24 1.65 1.30 6.81 1.30 1.20 6.88 1.125 1.075 7.11 1.025 1.025 7.47 0.97R 0.975 0.975 7.76 0.95 8.09 0.975 0.95 0.975 8.36 0.95 8.67 0.975 0.96 0.975 8.89 0.95 9.25 0.97.5
Conclusions
The results show that the most sensitive mixture of a natural gas (of the composition given) and air is more easily ignited by an induction coil spark than the most sensitive mixture of methane and air; but the difference is small. The use of natural gas instead of methane for testing the safety of electrical machinery in explosive atmospheres is therefore on the side of safety. The most readily ignited mixtures of natural gas and air, under the conditions used in these experiments, are those which contain between 7.3 and 8.6 per cent natural gas.
Lead Industries Organized I Induction coil
Figure 2-Wiring
Diagram
Discussion of Results
The results of the experiments are listed in Table I and shown graphically in Figure 3. A comparison of the most sensitive mixtures of natural gas and methane shows that the natural gas ignited more readily than the methane, although the difference is not great. Also, as the percentage of natural gas or methane is increased or decreased ~2 25 I I I I on either side of the m o s t sensitive mix2 00 L0 E e tures, the energy re221,5 quired t o cause igni24 zs tion increases rapidly. g g 150 The most s e n s i t i v e zzo mixtures for the natu$E126 a3 ral gas lie between 7.3 eg 1W and 8.6 per cent. That natural gas is 1NFLAMMABLE ’ CAS PER loCENT l2 more readily ignited Figure 3-Relative Ignitibility of Methane t h a n methane is in and a Natural Gas by a n Induction Spark accord with the results obtained by Wheeler,g who determined the “relative @
J . Chem. Soc
, 125, 1860 (1924)
The lead industry has fallen into line with the large number of other basic industries which have combined for mutual protection and for the dissemination of accurate and authentic information. This action was taken a t a meeting a t the Roosevelt Hotel, New York, N. Y., of representatives of practically every large corporation in the country engaged in the production, distribution, marketing, and consumption of lead and lead products. The organization will follow closely the lines of the Iron and Steel Institute and of the recently formed copper association. The membership will comprise every large company in the industry engaged in business in the United States, Mexico, Canada, and South America. Leaders of the industry said that such a plan had been under consideration for some time and that it had been speeded by the success of similar organizations in other nonferrous ‘metals. Clinton H. Crane was named president of the organization, Hamilton M. Brush, and Ralph M. Roosevelt, vice presidents; and Felix E. Wormser, secretary and treasurer. Headquarters officers have not yet been chosen. The name of the organization will be the Lead Industries Association, and it will engage in the collection and dissemination of accurate information regarding the uses of lead and lead products and statistics on production, distribution, and marketing. The thirty-four corporations, all engaged actively in some branch of the lead industry, who formed the organization are as follows: Ahumada Lead Co. American Lead Co., American Metal Co., Andrews Lead Co. American Smelting and Refining Co. Bingham Mining Co., Bunker Hill add Sullivan Mining and Concentratidg Co. Cerrode Pasco Copper Co., Chief Consolidated Mining Co., Consolidaied Mining and Smelting Co. of Canada, Ltd.; Eagle Picher Lead Co., ,El Totosi Mining Co. Evans Wallower Lead Co. Federal Mining and Smelting Co. Federated Mrials Corp Fleck Brothers bo., W. C. Fuller Pr Co., General’Cable C o . Gliddon Co.,‘Hecla Mining and Smelting Co., Metals Refining Co., Nationai Lead Co. Northwest Lead Co. Park Utah Consolidated Mining Co., Remingtoh Arms Co., Sherwin-Williams Paint Co., Silver Ring Coalition Mines Corp., St. Joseph Lead Co., Tintic Standard Mining Co., Utah Apex Mining Co., Utah Copper Co , United Meta!s Selling Co., U. S. L. Battery Corp., and U. S. Smelting, Refining, and Mining Co.
