THE ANALYST. 183 ON THE PRODUCTS OF COMBUSTION OF COAL GAS. By C. HEISCH, F.C.S. Now that the excitement of Parliamentary contest is (at least for the present) over, I think it may be well to lay calmly before your readers some, at least, of the reasons which have led me to the conclusion (shared, I am glad to find, by Silliman and other good authorities,) that the greater part, if not the whole, of the sulphur contained in coal gas, is converted during combustion into snlphiiric acid.As there can bc no question that sulphurous or sulphuric acid must be the result of tlic combustion, the investigation is really confined to establishing the presence of one or other, or both, of these compounds in the air of a gas-lighted room. My experiments were first directed to establishing the presence or absence of sulphurous acid.I n a small room, containing only 292 cubic feet of air, an ordinary batming burner, consuming 4 cubic feet per hour, was burned continuously for from 24 to 48 hours. The gas contained an average of 22 gr. of sulphur, per 100 C.F. The only ventilation was the want of absolute tightness in the door and window, and one or two chinks in a boarded parti* tion.Pieces of paper moistened with a solution of iodic acid and starch paste were suspended in various parts of the room, but no coloration was to be found, though in this small space from 20 to 40 grs. of sulphur were burned dJring the different experiments. This was repeated many times, and on one occasion only, two of the slips of paper were dis- colored : one of these was supended directly over the burner, the other over one of the chinks in the partition, before mentioned, so as to catch any outward draught there might be.An examination of the gas was conducted in the ordinary way, at the same time, and on this particular day the gas contained nearly three times as much aniulonia as usual, which led to the belief that the discoloration of the paper was due to some nitrous compound formed by the combustion of the ammonia, and not to Sulphurous acid.This idea was confirmed by the fact that when the gas was passed through acid before being burned no discolouration occurred. This experiment was many times repeated, always with the same negative result. Much stress has been laid by some on the fact that if the gas be burned in a Referees’ sulphur apparatus without ammonia, little sulphuric134 THE ANALYST. acid is condensed, and, impressed with the idea of the high boiling point of that acid, the conclusion has been arrived at that if present it must be condensed. By connecting the end of the eduction tube of the Referees’ apparatus with a good condenser, I found that much more sulphuric acid could be obtained, showing that it did pass out of the eduction tube, though there is no doubt a large amount of sulphurous acid is formed in the apparatus.Does the combustion, then, in this apparatus correspond with the ordinary combustion in a room where the products of combustion are at once mixed with an enormous excess of air? To test this several analyses were made of the air from the eduction tube, and it was found to contain only from 13 t o 14 per cent.of oxygen, and 4 per cent. of carbonic acid; indeed it extinguished the flame of a taper when brought in contact with it. Having thus shown the difference between experiments, conducted in this apparatus an6 the ordinary combustion of gas, I made the following experiment to see how soon the sulphurus acid from the eduction tube would oxidize if brought into the air.A common lamp chimney, 7 inches long and 2 inches wide, was suspended over the end of the eduction tube, so as to receive the ascending current of hot air. Paper moistened with iodic acid and starch was suspended in this, and though such paper was rapidly blued at the mouth of the eduction tube, half way up the chimney it remained uncoloured.I come now to the more positive proofs of the presence of sulphuric acid in the atmosphere of rooms in which gas is burned. I put on one side for the present all experiments with leather and metal goods, though in an economic point of view they are very important, and confine myself simply to the amount that can be condensed by merely lowering the temperature of the air, and its relation to the quantity of sulphur contained in the gas.I n the small room before mentioned gas was burned at 4 cubic feet per hour in a bat wing burner, after three hours a half-gallon flask full of powdered ice was taken into the room and left till the ice was all melted (about 3 hours). The flask was placed at 4-ft. 6-in. from the ground, or about breathing height.The outside of the flask was then washed with distilled water, and the washings precipitated with Ba C1. An averago of several experiments thus made with gas containing just over 20 grs. of sulphur per 100 cubic feet gave Hz SO, -3 grs. condensed. A similar set of experiments made with gas containing an average of 10 grs. per 180 cubic feet gave only H2 SO, 0056.Now as there can be no doubt that the mischief done by the acid formed must be, t o a great extent, in proportion t o the ease with which it is condensed, we have here a proof that the mischief increases much more rapidly than the actual increase of sulphur. These experiments are also interesting as showing that notwithstanding its very high boiling point, the condensing point of sulphuric acid, when mixed with air, is like all other vapours, altered very rapidly, according to the proportion of air with which it is mixed. This need not surprise us when we remember t h a t water which boils at 212O has been found in the state of vapour in the atmosphere at a temperature of-lOO* F, and there is good reason to believe exists at much lower temperatures. I am now engaged in a series of experiments to test those facts still more strongly and precisely, and these together with the experiments on the effect on metals and other bodies of the air of gas- lit rooms, I hope to lay before your readers on a future occasion,