138 THE ANALYST. ON THE PRODUCTS OF COMBUSTION OF COAL GAS. By G. W. WIGNER, F.C.S. FOR many years past this question has been thoroughly misunderstood. No doubt this may seem a very sweeping assertion, but when I find statements made by an eminent gas engineer, who is an ex-manager of gas works, that the question of the sulphur in gas is simply ridiculous, because sulphuric acid ‘‘ could not be formed and is not formed,” the matter becomes of some importance to meet and answer, and when further, this gentleman says in reference to the formation of sulphate of copper and sulphate of zinc caused by the burning of gas, ‘( it is ridiculous,” it is clear that there is reason to ventilate the subject. Now what are the actual facts? Gas, as originally produced from the retorts, contains at least two different and distinct forms of sulphur impurities. One of these is unquestionably sulphuretted hydrcgen, as is shown by its action on lead paper and other tests ; the other is either bisulphide of carbon or a closely allied substance.Oxide of iron entirely removes the former, i.e. sulphuretted hydrogen, but for the removal of the bisulphide of carbon the use of lime in some form or other is essential, and it is also essential that this lime should be used in a judicious and careful way.The contention of the gas companies throughout has been that the products produced by gas containing sulphur in the second of these forms, did contain sulphurous, but not sulphuric acid, while the contention of those who have thoroughly investigated the matter has always been that the product was sulphuric acid.I have recently carried out a series of experiments, and invefitigated the question, and will, as briefly as possible, describe them. I may state at once, that I do not at all doubt that just at the instant of ignition of the gas, and in the actual zone of the flame itself, a certain amount of sulphur has been burnt into the form of sulphurous acid only, so that if, for example, the products are drawn from a spot only half way up the chimney of an Argand burner, sulphurous acid will be found present, but this is hardly to be wondered at, when we consider that the combustion of the gas has reduced the oxygen present in the air by some five or lsix per cent., and replaced it by a corresponding quantity of carbonic acid. It is scarcely likely that oxidation could go on under such circumstances as these, but the moment these products of combustion leave the chimney of an Argand, or the globe of an ordinary batsming burner, oxidation again sets in, promoted largely, no doubt, by the amount of aqueous vapour present in the air, and the sulphur is oxidized into sulphuric acid, and becomes still more injurious in its effects.Having referred to the matter in this general way, I will now consider it in the special light of the experiments I hare carried on, to prove the correctness or otherwise of these deductions. The experiments were mostly tried in a room which was 10-ft. 6-in. high, and had nearly 2,000 cubic feet capacity. The room had been ventilated by means of an ordinary Arnott’s ventilator, having an area of 36 square inches, but instead of continuing the ventilation through this, a series of plate glass tubes about 16-ft.long and of the same area, viz., 36 square inches, were constructed, and the ventilation was allowed to take place through these tubes. This was effected by carrying the tubes round two sides of the room, so as to put the opening of the ventilator in a position nearly opposite to the old position of the Arnott’s rentilator, over the fire place,THE AXALYST.139 and in order to prevent any obstruction to the draft the ventilator was changed from a natural one into an artificial one, i.e., instead of taking place from the lower specific gravity of the heated air, it was artificially forced by means of a small jet of steam in the chlmney, and regulated to such an extent as to keep the room during the experiments at a temperature fairly accordant with the number of burners going. The fire place was stopped UP during the experiments.These tubes t o which I have referred, and which fornied, in fact, the ventilator of the room, were then used as follows :-The first tube, which was about 5-ft.long, was surrounded with ice so as t o cool the escaping air, and condense, as far as might be, any condensible vapour which existed in the products of combustion, and the cooling effect was sufficient to bring the air at the end of this first tube t o an average teniperature of about 80" E: the products of combustion thus having been drawn from a level, some three inches below the ceiling, at a temperature of nearly looQ 3'.The next tube, of about 4-ft. in length, mas used to contain various articles, such as pieces of colored silk and other dress materials, which were exposed t o the current of air in order to test the effect which was produced upon them, and this tube also contained a number of pieces of test papers of different kinds (which I shall refer to afterwards), in order to ascertain whether sulphuric or sulphurous acid was given off.The next-four tubes were each of short length, and were filled with glass Bubbles kept moistened with water, or with solutions of alkalies or baryta salts, so as to absorb any sulphuric or sulphurous acid which might have been given oft'; while the last tube of all contained an air meter, so fixed as to register the exact quantity of air which passed through the apparatus, or in other words the amount of ventilation of the room.There was practically no escape for the air from the room, except that which took place through this apparatus, and the only way in which the products of combustion could escape condensation was by their passing too rapidly through the tubes, and consequently still existing in a state of vapour instead of being absorbed.I carried on the experiments under extremely varied circumstances, sometimes using three ordinary fish-tail burners, which would be a good average amount of liglit for a room of such a size ; on one or two occasions using eight burners of various kinds, some Argand and some batswing ; on one or two other occasions using only one burner, and not consuming more than 4-ft.of gas per hour. I n every case the gas was tested during the whole time the experiment was going on, by the Referaes sulphur test, to ascertain the amount of sulphur which it contained, and the gas was supplied to the burners through an independent meter, so that the quantity of gas burned was accurately known.The amount of gas consumed during each experiment varied from 34-ft. to 350-ft. The gas tested was of varying quality; sometimes the sulphur in it was as low as nine grns, per 100 cubic feet, while, in one case, it ran up t o 185 gmu. per 100 cubic feet. The burners which I used were, as I have said, of all kinds, Argand, batswing, and fish-tail.The experiments therefore resolve themselves into this :--That a room was ventilated, artificaliy it is true, but in the ordinary way, viz., at the ceiling, and at the ordinary speed-and that the air escaping from the ventilator was cooled and tested. First as to the sulphurous acid; during the whole of the experiments a piece of iodide of starch paper was exposed to the effects of the products of combustion, of something like 6,000 cubic feet of gas, and at no one time was there any discoloration of it, that is, it was exposed for about 180 hours to the products of colvbustjon of ordinary coal gas, ranging from good to inferior 1 now come to the results of my experiments.140 THE ANALYST.quality, passing through a small tube, and yet there was never sufficient sulphurous acid to tint it in any way, although part of it was continually kept moist.Another piece of the same paper, prepared in the same way, was in twenty seconds tinted to a heavy blue tint, by the combustion of on17 5 grs, of bisulphide of carbon in a room of similar sizc. I am, therefore, quite justified in saying, that vhatever the products of combustion mag be, while they are within the chimney or globe of the gas burner, yet that the moment they are discharged into the room itself, the sulphurous acid which may have been produced, is entirely oxidised and sulphuric acid is the result.Having obtained this result, I will now consider the question of the amount of sulphuric acid which can be recovered from these products of combustion, and looking at this it must not be forgotten that sulphuric acid, like all other liquids, is volatile even at ordinary temperatures, and consequently exists in the air in a state of vapour, which even at low temperatures it is extremely difficult to remove or absorb.I n the morst of my experiments, while burning in the experimental room six large burners which consumed an average of nearly 40-ft.of gas per hour, I succeeded in recovering in the form of sulphuric acid 22 per cent. of the total sulphur present in the gas, a very considerable proportion of which was present as free and not combined sulphuric acid, while, in the best of my experiments, when I was burning only 1.5-ft. of gas per hour, i.e. lighting the room in the proportion in which an ordinary dining room would be lighted, I succeeded in recovering as sulphuric acid more than 62 per cent.of the total quantity of sulphur present. Therefore nearly two-thirds of the sulphur was formed into corrosive acid, and, in my opinion, it is not only justifiable, but right to assume that the air passing away through these tubes, carried off in the form of vapour the remaining one-third as sulphuric acid vapour.It now becomes important to see to what extent these results are corroborated by other experiments which hare been made in order t o prove an opposite supposition. I would, first of all, say that the result of the exposure during the whole time oE thc iodide of starch paper proves that there was no sulphurous acid, and that, therefore, all we have to consider is, whether my experiments as to the production of sulphuric acid are capable of corroboration, and I think they are.I find, for instance, from some evidence which Dr. Odling gave in an earlier part of this year, that, burning gas containing 33 grains of sulphur per 100 cubic feet, at the rate of 15 cubic feet per hour for 5 hours consecutively, in a room having a capacity of 8,800 cubic feet he found at a height of 1-ft.6-in. from the ceiling, -160 of a grain of sulphur per cubic foot of air ; at a height of 5-ft. 6-in. from the ceiling, -056 of ti grain per cubic foot ; at a height of 3-ft 6-in. from the floor, *59 of a grain per cubic foot. I f we take the mean of thcse results, multiply them by 3,800 cubic feet, i.e.by the capacity of the room ; this would amount to as much sulphur in the form of sulphuric acid as would be produced by gas burned for 40 consecutive minutes; in other words, if the ventilation of the rooms were so bad that the air was not changed more than once in 40 minutes, Dr. Odling would have succeeded in finding the whole of the sulphur which would have been given off by the combustion of the gas.Dr. Stevenson and Dr. Russell also obtained very similar results ; their experiment8 were of a different kind, and took the form of hanging plates upon the wall in order to ascertain how much acid condensed upon the surface of the plates. Some of the plates were clean glass ones, and some were iLoistened with au alkali, but when we calculatedTHE ANALYST. 141 these results, we found that in Dr. Stevenson’s drawing room, the area of which is about 3000 cubic feet, the amount of sulphuric acid deposited on the wails of the room is about 9-4 grains per hour, or according to his figures 42 per cent. of the total quantity of sulphur present in the gas burnt. A more striking confirmation of the presence of sulphuric acid in the products of combustion can scarcely be wanted. It is quite clear, therefore, that whether the injurious effects of sulphur in gas have or have not been over- rated, sulphuric acid is the product which is formed during the combustion.