number of slot meters in London; and the average consump. tion per consumer was 18,000 cubic feet, as compared with 6000 cubic feet in Scotland. The PRESIDENT said they must thank Mr. Lighbody for con. tributing so valuable a paper. Mr. FORBES WADDELL (Forfar) read the last paper, entitled OBSERVATIONS ON RETORTING AND CONDENSING Calculating on bases supplied by respected authorities, it is found that, even in the best forms of regenerative settings, the coke required to gasify one ton of coal has a calorific value of 4,914,000 B.T.U.; while the amount of heat required to gasify the coal is represented by 809,760 B.T.U.-less than one-sixth of the value is used for its proper purpose. There is, of course, to be reckoned the heat energy lost in getting through the material of which the retort is made, and the maintenance of the internal surface of the bench walls at just the same temperature as the retorts, &c. But even allowing a reasonable amount under these heads, there is certainly a great quantity of heat wasted or badly applied in retort-houses. In the first place, the retort-houses are kept warm at the places where the men have to do the hottest work. But we are prone to get used to things not being as they should be; and, though we admit that there is a lot of heat expended on the men and their surroundings, we have to be content with the conditions. These conditions are, however, unsatisfactory; for they are evidence of heat badly applied at the best, or altogether wasted. 66 'Altogether," of course, refers to heat expended on floors, walls, roofing, and the air which at times rushes very rapidly over the bench surfaces; and "badly applied " is sug. gested to me by coals being dried in front of retort-benches in winter. The latter instance, perhaps, looks somewhat of a paradox; but when it is considered that the coal must be kept more than 20 feet from the source of heat, one must admit that the drying is done at great expense, though it is certainly better than letting the heat radiate on to the wall. Retort-house walls, to my knowledge, sometimes get too hot for the hand, though there are many openings in the walls of the house referred to. On the other hand, the mouthpieces of retorts in action sometimes get cold enough to handle. In considering whether a remedy, or a partial remedy, can be found, this occurred to me: In a setting of brick-built retorts 4 inches thick, with a 4-inch front wall, there is never the least tendency on the part of the front surface to become red hot; though it is observed that, at the end of a charge, the retort is a bright red. Further, the same temperature is applied to the brick retorts as to the front brick wall; and, therefore, if a door were put over part of the front wall, that part would soon get red hot, and would keep so as long as the door was shut. The door being closed only keeps the air off that part of the wall; and the two results are: (1) bricks get red; (2) air passing over that part is not much heated. Here, however, another point occurs to me. Say that there is within the setting (I have not attempted to use thermometers therein) a temperature of 2000° Fahr., and at times the hand can be put on the mouthpiece. Then there is a difference of nearly 2000° between the temperature surrounding the retort and that round the mouthpiece; and though the latter is seldom so cold as to be handled, there is at all times a very great difference, which must mean a rapid fall in the temperature of the products of the distillation of the coal. From a very early period in the history of gas making, managers have been exhorted to cool such products very gradually; and the importance of doing so is being brought home now with more force than ever it was in the past. It is no new thing to take the gas out of tars. There have been a good many ways, of which I presume the most outstanding are the Dinsmore and Peebles processes. Both have shown remarkable results. Mr. Isaac Carr, of Widnes, in a paper read before the Manchester District Institution of Gas Engineers,* said that by passing the distillation products, on their leaving the retort, through a heated duct, the quantity was increased 10 per cent., and the quality by 4 or 5 candles. From the distillation of one ton of tar in the Peebles plant, according to Mr. Bell, there are obtained about 15,000 cubic feet of 25-candle gas and 15 cwt. of excellent coke. In Blairgowrie, I made some slight alteration of the fittings of a setting of three retorts with the view of condensing as much tar as possible, and returning it to a specially heated part of the ascension pipe; and the results were so good that at the time I was sceptical, but was ultimately quite satisfied as to their accuracy. It has, therefore, been interesting to me to further experiment with these two points before me: (1) The saving of heat and returning it to the setting; and (2) cooling the products of the distillation of the coal more gradually. My aim has been to bring about at a single retorting the gasification of as much of the coal products as possible, with the lowest expenditure of See " Reports of Gas Associations" for 1889, p. 396, and for 1890, p. 74. the coke produced; and these modifications have suggested themselves to me, and been carried out from time to time. The temperature of the gases surrounding the retort being (say) from 1800° to 2500° Fahr., and that of the air playing about the mouthpieces and ascension-pipes from 50° to 100° Fahr., there is, in addition to the sudden cooling, a great fluctuation-more sudden as the temperature of the atmosphere falls, and improving as it rises. This fluctuation is from day to day and from season to season. The experimental plant was, to begin with, an iron retort, Liquor Overflow Hydraulic Main Overflow into Tar Overflow FIG. 13.-ARRANGEMENT FOR CONDENSING HEAVY TARS AND RETURNING THEM TO MOUTHPIECE. 3 feet long by 7 inches diameter, and other plant corresponding. The first help to more gradual cooling that suggested itself was a larger ascension-pipe, giving increased duration of travel from the retort to the hydraulic main, and thereby, according to our best authorities, giving gas of increased illuminating power. The first arrangement had the stand-pipe 1 inches diameter, and it was substituted by one 3 inches diameter, provided with a cooling vessel at the top (see fig. 13). At this point, I cannot refrain from saying a few words on my experience of different diameters of ascension-pipes, the choking of which has given most managers some trouble. First, they are simply a means of conveying gases and vapours from the retort to the hydraulic main; and although those who are troubled with chokes in them might well reason, even from a mechanical point of view, that, if there was more room for pitched tars, there would certainly be fewer chokes, still the pipes I come across are not being much increased. In addition to the extra area, there is greater cooling surface. An 8-inch pipe, for instance, has an area of fully 50 square inches compared with an area of 23-7 square inches in a 5-inch pipe. The comparative rates of travel through 54-inch and 8-inch diameter pipes are as their areas; so that the cooling efficiencies of the two are (respectively) 409 and 12,600-that of the 8-inch pipe being three times that of the 5-inch pipe. One thing that change has brought about is the complete absence of chokes. I have not had a choked ascension-pipe for five years. In very cold weather, however, even with high heats, there is liquid tar on the mouthpieces-evidence that a great quantity of hydrocarbon vapours is being condensed in the mouthpiece, where the temperature is much greater than in the hydraulic main. At other times, with no better heat in the setting, but with warmer air round the mouthpieces and ascension-pipe, the former is quite dry; and from the tar coke on the mouthpiece, it is evident that a good deal of tar has been gasified. The last modification made is one that, while controlling the temperature of the air round the stand-pipes, returns to the setting the air which, in cooling the ascension pipes, mouthpieces, and bench front, becomes itself heated. The diagram (fig. 14) FIG. 14.-SUGGESTED METHOD OF HEATING MOUTHPIECE AND AIR FOR COMBUSTION. illustrates the setting and ascension-pipe covered with sheet-iron in such a way that the chimney draws all the air needed for the producer and combustion chamber down between the bench surface and the bench front covering. The advantages of this are two: (1) There is, in the first place, brought about that desirable gradual reduction of temperature, or the cooling is at any rate more gradual; for, instead of the air first getting into contact with the mouthpieces when at its coldest, it commences to cool the top of the ascension-pipe, and as it gets warmer, descends to cool the mouthpieces and, indirectly, the distillation products. That order of things-the cold air first cooling at the top-means the falling out of a greater quantity of heavy tars than is the case in ordinary practice; and, further, it means the retention of hydrocarbons in their gaseous state at the mouthpiece, by reason of the air coming into contact with the mouthpiece being first heated, and on that account not cooling the coal products so rapidly. (2) The other advantage is in the air, thus heated by contact with the ascension-pipe and mouthpiece and with the bench walls' surface and the inside of the covering of the bench front, being still further led over the bench surface, till, when entering the producer and secondary-air flues, its temperature has been increased from (say) 70° to 500° Fahr. The result of this arrangement, considered in relation to better results in make and quality of gas, is tabulated side by side with results from the plant under the other conditions already mentioned. The saving of coke was quite appreciable, even with the experimental plant; and in view of this, the figures for coke-saving per ton of coal carbonized may interest you. Counting on each ton of coal producing 13 cwt. of coke, and allowing that 25 per cent. of the coke made is required to keep up the heats, we have 13 X 112 X 25 364 lbs. of coke used per ton 100 = of coal carbonized. Say that each pound of coke requires for its combustion only 12 lbs. of air-not much more than the theory figure-then the amount of air required for firing per ton of coal carbonized is: 364 X 12 = 4368 lbs. The specific heat of air being 0.238, and all the air required for combustionthat is to say, 4368 lbs.-being heated through a range of (say) 430° Fahr., then the heat given back to the setting in this way means 4368 X 430 X 0°238 : That is a saving in coke at the rate of 33 lbs. per ton of coal carbonized; and I may say the estimate is very moderate, as the air was heated to the extent calculated by taking back only the air which had heated the front surface, while the air heated in the remaining surfaces was allowed to escape through the roof. A further disadvantage with this experimental plant is that the jacket protecting the bench front is of thin sheet-iron, which is not a good non-conductor. I have not had a brick covering tried; but I have no doubt it is quite applicable to a working setting, in which case I believe a temperature of about 700° Fahr, could be maintained about the mouthpiece. Such a |