UNIFORM MOVEMENT OF FLAME ETC. 841 LXX1.-The Uniform Movement of Flame in Mixtures of Acetylene and Air. By WILLIAM ARTHUR HAWARD and SOSALE GARALAPURY SASTRY. IN continuation of the revision of previous work on the propaga-tion of flame t h a t is b’eing carried out a t the Home Office Experi-mental Station under the direction of Dr. R. V. Wheeler we have determined the speeds of the “ uniform movement ” in mixtures of acetylene and air. It may be recalled that the “uniform movement” occurs when an inflammable mixture of gases is ignited a t tho open end of a horizontal tube closed a t the other end and is usually regarded as the normal speed of propagation of flame from layer t o layer of the mixture by conduction of heat (Mallard and Le Chatelier, Ann. des Mines 1883 [viii] 4 374).Previous determinations of the speed of the uniform movement in mixtures of acetylene and air have been made by L0 Chatelier (Compt. rend. 1895 121 1144) who used a glass tube 4 cm. in diameter. The speeds recorded were : Acetylene in mixture. movement. Speed of uniform Per cent. Cm. per second. 2-9 10 8.0 500 9.0 and 10.0 600 22.0 40 64.0 5 I n a later publication namely “ Le Carbone ” (Paris 1908) Le Chatelier gives intermediate values : VOL. CXI. Acetylene in mixture. Per cent. 5.0 7.0 15.0 40.0 60.0 Speed of uniform movement. Cm. per second. 200 400 300 22 7 L 842 HAWARD AND SASTRY THE UNIFORM MOVEMENT OF but it is not clear whether these arc3 actual determinations or numbers interpolated on a curve constructed from the &x results recorded in the Comptes rendus.Le Chatelier thus describes the curve he obtained (Zoc. cit., p. 280): “La courbe . . . prdsente une forme toute sp5ciale; elle se compose de trois droites une droite montamte et une descendante se coupant pour la vitesse maxima vers 10 p. 100 d’acdtylhne puis ensuite une droite tres peu inclinee coupant la Fecond Q la teneur de 20 p. 100 e t se prolongeant jusqu’i la limite d’inflammabilitd supdrieure. Ce troisihme segment de la courbe correspond Q la combustion avec flamme fuligineuse et dBp6t de charbon. Au-dessous de 20 p. 100 il ne se forme par la combustion que des produits gazeux acide carbonique oxyde de carbone et hydrogbne.” Our own experiments were made in a glass tube 12 mm.in diameter and are not therefore directly comparable with Le Chatelier’s so far as the absolute measurements of speeds are con-cerned. It is permissible however to compare the shapes and characters of the two curves. We can confirm the statement that mixtures containing more than about 20 per cent. of acetylene deposit soot owing t o decomposition of excess of acetylene and that the speed of propagation of flame in such mixtures is slow; but we cannot agree that the curve can be represented by gtraight lines. As with mixtures of other inflammable gases and air there is a gradual flattening of the curve towards the limits and the maximum speed is obtained over a range of mixtures containing between 8 and 10 per cent. of acetylene so that the crest of the curve also is flattened.The speed of the flame in mixtures containing more than 20 per cent. of acetylene decreases gradually as the percentage of acetylene is increased. The mixture of acetylene and air for complete com-bustion contains 7.75 per cent. of acetylene; the fact that the fastest speed of flame is found in mixtures containing rather more than this can be explained on the assumption that the thermal conductivity of acetylene is higher than that of air (compare Haward and Otagawa T. 1916 109 83). Our results are shown graphically in the diagram. EXPERIMENTAL. The method of experiment and the electrical means of measuring the speeds of the flames were the same as employed by Wheeler (T. 1914 105 2606). The acetylene was obtained compressed in cylinders without acetone as solvent and was of a high degree of purity (98 to 9 FLAME IN MIXTURES OF ACETYLENE AND AIR.843 per cent. C2H2). The mixtures were made over brine in metal gas-holders of 70 litres capacity and were analysed before use; the explosion tube was filled with the required mixture by dis-placement of air six times the volume of the tube being used. The initial temperature of the mixtures was that of the room ( 1 5 O to 20°) and they were saturated with water-vapour at that temperature. Ignition was by means of a lighted taper which was drawn rapidly past the open end of the tube. The speeds were meamred 2 4 6 8 10 12 14 16 18 20 Acetylene per cent. between two points 40 cm. apart the first point being 10 cm. from the open end of the tube. I n addition to the experiments recorded in the diagram for which a tube 12 mm. in internal diameter was used the speeds in tubes of 9 mm. and 25 mm. diameter were also determined. The speeds in the 9 mm. tube w0re rather slower than those obtained in the 12 mm. tube but the shape of the curve was the same. With the larger tube 25 mm. the duration of the uniform movement was too short to admit of accurate measurement by the means employed. IMPERIAL COLLEGE OF SCIENOE AND TECHNOLOGY, SOUTH KENSINGTON S.W. [Received August 9th 1917.1 L L