1861 the view, it seems, was that carbon is liberated because of a supposed greater affinity of oxygen for the hydrogen of the hydrocarbon than for the carbon, there not being enough for both. But these points had to be tested.
In the study of the chemical changes that take place, a flame burning at a circular orifice offered the best conditions. As explained in text-books of chemistry, such a flame may be thought of as being made up of an inner, faintly luminous cone fitting into an outer, brightly luminous one—as a finger fits into a glove finger—this latter being surrounded by a non-luminous sheath of water vapor and carbon dioxide. It was desirable to separate these two cones, in order to study the gas after it had left the inner cone and before any change had been brought about by the conditions existing 
in the outer cone. This separation was first accomplished by Techlu, in France, and Arthur Smithells, in England, working independently, with a piece of apparatus, the essential features of which are pictured in cross-section in Fig. 1. By a proper control of the relative proportions of gas and air the inner cone was made to burn at the orifice i, while the outer cone burned at the orifice o. The outer cone got its oxygen from the surrounding air, while that for the lower flame was supplied along with the gas. The temperature of each cone was measured and the gases entering and leaving each were analyzed. It was found that as the proportion of gas to air was increased, the tip of the inner or lower cone became brightly luminous and a column of soot passed upward through the tube, becoming faintly luminous in the outer edge of the upper flame. As soon as the inner cone becomes luminous the unsaturated[1] hydrocarbon compound known as acetylene begins to appear among the gases passing to the outer cone.
Vivian B. Lewes now attacked the problem as to how carbon comes to be in the flame in the free state. He analyzed gas drawn from different parts of a coal-gas flame, measured the temperature of its different parts, etc., publishing his results between 1893 and 1895. These results may be stated as follows: Coal-gas consists mainly of a mixture of hydrogen and hydrocarbons, both saturated and unsaturated. In an ordinary 'fishtail' burner flame all hydrogen is consumed before the middle of the luminous portion is reached. Of the saturated hydrocarbons about seventy-five per cent, disappears as such in the dark por-
- ↑ The terms 'saturated' and 'unsaturated' have reference, among other things, to the relative quantity of hydrogen to carbon in the molecule, an unsaturated compound having relatively less hydrogen than a saturated one.
