and York D retorts, consists only in an extension of surface upon which the coal is spread, the latter varying from eighteen to thirty inches in width, and about the same dimensions in length and height. These cast-iron retorts are set in benches of from two to nine in a set, usually enclosed in an arch of brick work, heated with one or two fires, arranged with shielding tiles, so as to prevent a direct action of the flame upon the metal. Some with ascending, some with descending flues. To describe the particular mode of setting on each plan, would require drawings in detail; a labour entire ly uncalled for, as the proper plans will be prepared of the arrangement deemed most effectual. In addition to these, I have found retorts, or ovens, composed of fire brick, built in form, or of clay moulded to the shape in the arch constructed to receive it, varying in dimension and shape from two to four or five feet in width, which will be treated of in the sequel. The plan of retort, and the system of working to produce the greatest quantity of gas, of the best quality, is at present a subject of controversy among engineers; and to form a just opinion, requires a careful comparison of the operations of each. As the whole economy of gas making depends upon the expense of carbonization, it was an object of much solicitude to obtain from the books at the respective works, such statements of their daily operations, as would enable me to form a correct estimate of their advantages, rejecting mere theoretic opinions and verbal statements, if unaccompanied by satisfactory testimony. In giving the general result of these examinations, it will not be requisite to record the names of the works, as such a publication would be a betrayal of confidence, highly unjustifiable. These statements have been generally obtained for a short period of time, to avoid multiplicity of figures; but have been compared with the workings for much longer periods, often six and twelve months: the results may, I think, be received with confidence. The following have been taken as the elements of comparison: 1st. The quantity of coal used for carbonization and fuel. 2d. The product of coke in weight. 3d. The product of gas, and quality. use, is to fill the retorts with coal, leaving space for the increased bulk of the coke, and for the insertion of tools for its removal, carbonizing with a moderate heat, and allowing the charge to remain exposed to the action of the fire for six or eight hours. The opposite to this, is to charge the retorts with less coal, or a thinner strata, and to increase the temperature, so as to work off all the gas contained in the charge in three, or at most, four hours. By the first mode of operating, less fuel is required to carbonize the same weight of coal, and the retorts being subjected to more moderate heat, will remain fit for service a longer period of time. It is therefore contended by its advocates, that the saving of fuel and saving in retorts, more than compensates for any advantages to be obtained by the short charge system. The opposite doctrine is not new, having been held and practised in the early stages of the art, under many practical disadvantages; but the more easy operations on the long charge system, have been practised in a majority of the works using the bituminous or soft coal. The attention of several skilful engineers has of late been directed to an improvement in the quality, and increase in quantity, of gas produced, which they have effected, in a material degree, by operating with high temperatures and a thin strata of coal. Their practice has been founded upon the following theory: That the first products from the distillation of coal, after the water has been evaporated, contains the greatest quantity of olefiant gas, and consequently has the highest illuminating power. That if this gas be evolved at a high temperature, it carries with it, in combination, a portion of carbon, which, at a low temperature, would not be disengaged as gas, but would pass over as tar. That, as the process advances, the proportion of carbon evolved diminishes; while the proportion of sulphur increases. That after the first two hours, the quantity of gas and its specific gravity diminishes in a rapid grade. To test the accuracy of this theory, certain experiments were instituted, intended to ascertain the quan. tity and quality of the gas evolved during different periods of its distillation, varying the quantity charged By deducting the second from the first, we shall have at each time, the temperature at which it was carbon-. the nett amount of material consumed to produce theized, and the duration of the process, so as to embrace third element, or product of gas, in cubic feet, its quali ty being considered generally. This mode of comparison has been preferred to the more usual estimate of ascertaining the proportion of fuel used, to the coal carbonized; because the latter method is liable to error, as the quantity and quality of the gas is improved by adding to the temperature at which the distillation is carried on, and consequently increasing the amount of fuel burnt. In this comparative view, all residuums, save the coke, are rejected; not because they are worthless, but on account of the great difficulty in obtaining a correct statement of the quantity made, and variation in value of the other residual matters. The vast quantity of tar and ammoniacal liquor, made in Great Britain, has rendered them so far unsaleable, that the latter is often evaporated under the retorts or flues, and the former accounted of more value, as a fuel for heating retorts, than as a marketable product. Such residual matters, therefore, in a comparative state. ment, do not constitute an item of sufficient importance to affect the result in an appreciable degree, though some difference must exist in the quantity of tar made, when very high degrees of heat are used in the carbon izing process. The system of carbonization which has longest ob tained, and which at the present day is in most general a fair comparison of the two modes of working. The next experiment, made with the same retorts, heated to a higher temperature, charged with one hundred and forty pounds each, and worked off in six hours. The gas produced from this charge of two hundred and eighty pounds, was seventeen hundred and fifty feet, or in the ratio of eighteen thousand feet of gas per cha'dron: six sevenths of the whole product being evolved in four hours. Specific gravity 5.18. The charge being then reduced to one hundred and twenty pounds to each retort, or two hundred and forty pounds total, was worked off in five and a half hours, producing the same ratio of gas to the chaldron Eleven-twelfths of the whole product being evolved in four hours; the product in gas, evolved after the four hours, not being worth the fuel taken to produce it, By carefully repeating these experiments, and taking the specific gravity at various stages of the process, it was found to decrease in each successive half hour, as the work progressed, after the second or third trial; while the result, as respected quantity, proved equally in favour of the short charge system. The result of these experiments clearly establishes the fact, that the greatest quantity of gas, and the best in quality, may be produced by working a diminished quantity of coal in the recipient at a high heat. So far, therefore, as quality and quantity of gas produced are concerned, the principles to be followed are, 1st. An extended surface, and thin strata of coal in the retort. 2d. Rapid carbonization, at a high temperature. From the insulated experiments, such as have been detailed, no judgment can be formed on the other points of comparison; although care was taken to note the quantity of fuel used in each experiment, the correctness of the statement cannot be assumed as a guide to continuous work. To determine the expense of fuel, required under different circumstances, recourse must be had to the continuous operations of works using the same material for carbonization, and dividing the amount of fuel into the product of gas made, instead of the quantity of coal carbonized; for this mode of estimation the reasons have been given. 5.40 4.80 6.44 do do do do No. 1. London D, 4 hour charges, 5.75 feet to pound. 2. do. 6 hour do 4.60 "3. York D, 44 hour do 4. Elliptic, 6 hour do "5. York D, 4 hour do The quantity of gas produced from a pound of material used, and the quality, as indicated by the specific gravity, invariably gives the advantage to the short charge system. It should be observed, that the coke produced upon this system, is lighter than by the old plan, and the bulk increased. These points being established, we are next to comThe statements now presented are from works car-pare the economy of the plans respectively taking into bonizing New Castle coal, at four and six hour charges. view the wear and tear, and the labour required to As I could obtain no returns from works using the same keep up the supply. coal at eight hour charges, the comparisons will be confined to the two first, which are sufficient for our It does not necessarily follow that an increased temperature will create a corresponding increase of wear in the retort, as variable heats have a much greater ef fect upon them than high heats, if they are kept uniform. The results are not so disastrous upon the retorts used in the short charge system, as might be supposed, provided care is taken to keep the temperature the same; but the difficulty of keeping high hea's equable, exposes the retorts worked on this system, to greater risks than by the opposite plan:-to determine, therefore, what will be the duration of them,is difficult,as experince on a large scale has not yet been had to settle this point; although in small works, whose operations have been brought immediately under the eye of the engineer, but little difference in duration has been found between the two plans Still it would not be wise to draw from their experience conclusions, and refer them to works on a larger scale, which must be entrusted to a greater number of stokers and which cannot be kept so completely under control. In Great Britain, the proportion of gas required during the summer months is so small in comparison to the other parts of the year, that during this period a great majority of the retorts are thrown out of service, consequently in a set of retorts, the usual duration of which is eight months, a sufficient number will be saved to do the work of the other four or summer months; for, except in large cities, the public lighting is entirely suspend. ed during that term, and the private lighting diminished in a great degree. In a work, therefore, in which the retorts can stand eight months active service, they will require renewal annually to keep the stock whole. In works operating with six hour charges, I have found a better average duration than here stated, and that two complete renewals in three years, being equal to working twelve continuous months may in general be calculated on. This duration is more than many works attain, and may be considered the highest average that can probably be allotted to them. Retorts working eight hour charges, often remain in continuous service eighteen or twenty-four months; indeed I bave known them thirty. No economy is derived from such long use, because, although the retort will not leak, the product is constantly diminishing, while the proportion of fuel increases from the contraced space in the retort occasioned by the solid particles of carbon which collect on its internal surface. Indeed this obstruction takes place shortly after the work. ing commences, and the incrustation increases so fast that it is doubtful whether there is much saving effected by retaining a retort in service past one season. But it is needless to go into minute calculation upon this point. If we lay aside the retorts working eight hours, and form the comparison between those working four and six hour charges we shall find that the additional duration of the last, is compensated for by the diminished number required to do the same work on the first plan, on account of the rapidity of the working, and the additional gas produced from the same material, leaving the wear and tear about equal. Thus to make 100,000 feet of gas, in twenty-four hours, by the six hour system, producing 11,000 feet to chaldron of New Castle coal, would require nine chaldron and four bushel. Say 41 retorts each, 2 bushel to a charge, 4 charges in 24 hours. 41+2+4 328 bushels, at 11,000 feet per chal. dron, 100,000 feet. To make the same gas by the short charge system, at 15,000 feet to chaldron, would require 6 chaldron, 24 bushels coal; say 27 retorts, one and a half bushel to a charge, 6 charges in 24 hours. 27+11+6=243 bushels, at 15,000 feet per chaldron, 101, 245 feet. Thus the number of retorts required to produce the same quantity of gas, bear the relation of 41 to 27. Now if the retorts, on the six hour plan, require renewing twice in three years, there will be required, for that period 41 + 282 retorts. While on the other system, lasting but one year, there will be required, 273, or 81 retorts. though many had tried them. At one station, I found two of his ovens in operation, which required as much coal for fuel as for carbonization; but this was accounted for in the thickness of the walls, which had been built of nine-inch brick, Independently of the high per centage of fuel, required by the ovens of this material, other difficulties occurred in the use of them which almost proved fatal. In the first place, it was found that the clay, unless made very thick, was a material of too little tenacity to resist any undue pressure; especially where the separate pieces were joined together by cement; and that any accident, occasioning a stoppage of gas in the pipes, reacted so violently as to burst or injure the retort. This difficulty was remedied by building stays or ties into the retort, connected with the outer arch. But the evil most difficult to be cured, was the tendency to leak at the junction of the cast iron mouth piece, and at the joints, owing to the contraction and expansion of the material under different temperatures. When the retorts are first brought to their heat, time will elapse before the cement in the joints attains the consistency of the other material, and becomes entirely gas-tight; but while the temperature is kept uniform, little difficulty is experienced when once they have been made tight. The constant variation in demand for gas, makes it incumbent on the manufacturer to vary the number of retorts in action, as it increases or decreases. Hence the necessity of letting down the retorts; an operation during which the joints, being the weakest part, give way as the brick contracts; and it is more difficult to refill these cracks than to make the original joints with fresh brick and cement. This difficulty has been partially overcome by filling the joints, before reheating, with clay cement, and washing them with a mixture of salt and pot-ash, or some other glaze. To produce a perfect retort of clay, the only desid Thus, not withstanding the duration of the retorts upon the four hour plan, is less than upon the other, when the expense of renewal is divided upon the quantity of gas made during an extended period of time, the diferatum wanting, is such a combination of material as ference is unappreciable; while the former possesses the advantage of requiring less space, and less capital in the original construction of the works. From this statement, it is evident that, as the labour must bear a proportion to the number of retorts at work, and the quantity of material to be handled, the advantage is decidedly in favour of the last named plan. In these remarks, reference has been had to cast iron retorts only; but so far as the amount of production is considered, they refer equally to the oven of Mr. King. will not be subject to change of dimension, from any change in the temperature, so that the fires may be let down and re-kindled without causing a waste of gas, To this end, Mr. Spinney of Cheltenham, an engineer of practical knowledge and skill in his profession, has instituted a vast number of experiments, and suc ceeded by a mixture of fire-clay, pipe-clay, and silex, in producing the desired results. The Cheltenham works, under the charge of that gentleman, are provided with retorts or ovens of this description entirely; and the operations of that compa These ovens, it has been observed, are made of mal-ny are conducted in a manner highly beneficial to those leable iron, and in point of economy in wear and tear, have a decided advantage over the cast iron retort, for the work they are capable of, requiring less fuel than many other works. interested, and to the public. Heretofore, single ovens, of a dimension smaller than Grafton's, have been used by him, each heated by one fire, and while the quantity of gas from the coal carbon. I should be much inclined to adopt them in prefer-ized, is quite as much as would be produced by the ence to the cast iron, were it possible to work them on the short system. The shape of these ovens is such, as to carry out the principle laid down to the fullest extent, but the extended surface of the bottom renders it impossible to heat them to the requisite temperature, without early destruction to their shape, and soon rendering them unfit for useful service; but I am not at all certain that the adoption of wrought iron retorts, of smaller dimensions, would not be conducive of advantage. The high price of iron, in this country, led me to examine with care into the plans in use, and experiments now making in England and Scotland, to carbonize in retorts or ovens made of fire-clay or brick. The original inventor of these ovens, was I believe, Mr. Grafton, of Cambridge; and one work in Brighton, now operates with them successfully. The manager of the station spoke of them favourably; but I could not obtain an exact statement of his operation; nor could I hear the same good opinion expressed elsewhere, same system of working in iron retorts, the fuel account is materially increased-the great saving being in the wear and tear, an item reduced to a very limited amount. In some new benches erected, Mr. Spinney has reduced the size of the retort still more, and set two to one fire, carrying on the carbonization at a lower rate than with the single oven; but this bench has not been in operation long enough to decide whether the saving in wear is not more than compensated by increase of fuel though, as far as a judgment could be formed, the result was satisfactory. It should be observed, that these works were operating with eight hour charges, and therefore not obtaing all the advantage which might accrue from using an indestructible material. I am inclined to think, however, that the clay retorts will be found a valuable acquisition to the gas maker in this country, and am confirmed in this opinion after examining the works of Scotland, in two of which From Moore's Philadelphia Price Current. FOR THE YEAR ENDING DECEMBER 31, 1834. the clay retorts are in constant use, with highly bene. ficial results Here, as well as in England, immense difficulties have been encountered in bringing them to perfection; but their efforts have been crowned with success. At the work in Glasgow, a fair example is offered of the value of this material, in comparison with iron retorts, in both of which the same species of coal is carbonized. The principles laid down, of working at high temperatures, are here carried to a greater extent than in any work in England, seven or eight charges being worked off in twenty-four hours, each retort being made to produce near five thousand feet of gas in that period. To enable iron to stand such excessive heats at all, it is necessary to shield them at all points with fire lumps, rendering them as inaccessible to the action of the fire as if they were composed entirely of clay. The result is in this case,that the fuel account is quite as high as with the clay, while the wear and tear is ten to one in favour of the latter material; for with their utmost care, it is difficult to preserve the iron retorts more than four months, while the clay lasts from twenty-four to thirty months, and costs far less in construction. The difficulty which exists in the iron retorts of contracting internally, in consequence of the deposite of carbon, has here been remedied in the clay retorts, by Occasionally leaving the interior in contact with the ac tion of the atmosphere a few hours, while at a red heat, the oxygen of which combining with the carbon, repa. rates it from the clay surface. In the work alluded to the most decided preference is given to the clay retorts, where, as well as at the Paisley work, which operates with brick retorts on the same principles, the quantity of gas procured from a pound of coal is ten or twelve per cent. greater than in those works using the same material, where milder heats, incident to the use of cast iron, are in practice Although from a careful examination of this subject, I feel persuaded that the use of fire clay-retorts will be found more conducive to economy than those made from any other material in this country, (where the price of iron is more than double its price in Great Britain, and that in the event it will be resorted to,) yet I am by no means prepared to recommend its immediate adoption. We have no reason to suppose that our skill will enable us to bring to perfection, at once,a material which has cost so much labour and loss to experienced engineers, who have for years been endeavouring to bring it into successful operation, and who have not yet brought it to that state of perfection of which it is evidently susceptible. The immediate success of an infant gas manufactory depends so much upon the first impressions with which it is received by the public, that it would be unwise to abide any risk of failure, by stepping out of the beaten track at the commencement, and I should by no means recommend any change from plans already known, and well tried. It will be ample time to make experiments for the improvement of the process and apparatus, when experience has made us masters of the business. I have therefore selected as the most suitable for the purpose, the retort described as the York D, of cast iron, set in such manner, with three to a fire, as will allow of the substitution of the clay retort, whenever such a change in the system of operating is deemed advisable. This retort has been selected, because, under all circumstances, it appears to be the one with which the principles laid down may be carried out with the best advantage, being large enough to give them free scope, and least likely to become distorted by the high heats to which it may be subjected in the process of carbonization. (To be continued.) FROM THE 30th SEPTEMBER, 1833, TO THE 30th SEPTEMBER, 1834. NEW FERRY STEM BOAT.-The Camden and Amboy Rail Road Company have had built a steamboat for conveying passengers across the Delaware, which is designed to fore itself through the ice. The bows of the boat are solid and covered with iron, and so constructed that it may be forced upon and by its weight break in the ice. The length of the keel is 90 feet, the breadth of beam 40 feet, and she is provided with a very powerful engine which has a 9 foot stroke, also with a spacious and convenient cabin. Her wheels and paddles are made very strong and protected by iron coverings from injury by the ice. We understand she came round from New York, where she was built, to this city, in 22 hours. RIVER DELAWARE. (Continued from page 8.) MR. DOUGLASS' REPORT. PRINCETON, Nov. 18th, 1834. To Garret D. Wall, Peter J. Stryker, and John M. Sherrerd, Esquires, Commissioners of the State of New Jersey, &c. Gentlemen:-In compliance with your instructions, I have made an examination of the Delaware river, with a view of ascertaining the best place to form a connection between the Pennsylvania canal and the Delaware and Raritan canal feeder-also the best mode of obtain. ing a supply of water for the use of the Pennsylvania canal, with the least injury to the navigation. Black's Eddy appears to combine more advantages, and offers more facilities for forming such a connec tion, than any other place. The eddy is caused by a projection of the main land from the Pennsylvania shore, contracting the river into quite a narrow space. The sudden widening out of the river below this point, creates a counter current, so that boats and rafts incline towards the Pennsylvania shore, and find no difficulty in landing at any stage of the river. Immediately below the eddy, the river takes a sudden turn to the east, forcing the current directly in to the head of Bull's Island, at the head of the feeder, so that boats or rafts,starting from the eddy drift, directly to the entrance of the feeder. The entrance to the feeder is about one mile below the eddy. The water from the eddy is of sufficient depth to float a vessel of six feet draft. If a connection is made at this place, it will be necessary to construct two locks of eight feet lift each, to get into the river from the Pennsylvania canal; also a tow path along the New Jersey shore, from opposite the eddy to the entrance to the feeder, which is all that will be necessary to form a safe and secure connection. Another place which offers some facilities for a con nection, is New Hope. In order to effect this, it will be necessary to connect the feeder with the river, by means of a short canal and lock of ten feet lift, and the Pennsylvania canal by a guard lock or lift lock. If by a guard lock, to insure a safe passage for the boats across the river, it will be necessary for them to run up the Pennsylvania shore some distance, before it will be safe for them to venture out into the current of the ri ver, for fear of being drawn over the dam. The water along the shore for a distance of about one hundred feet from it, is quite shoal; consequently, it will be necessary to excavate a channel three feet deep below low water mark, so as to admit boats of the same draft as the Pennsylvania canal; a tow path along the river bank will also be required. The point to which this channel should be excavated, is about twenty-four chains above the guard lock at a place called Poplar Reef. From this point to the place proposed to colinect with the feeder, there is sufficient depth of water to float any craft which can navigate the canals. I am apprehensive, if this plan should be adopted, the channel would be liable to be filled with a deposit from the river, and subject to receive damage in time of floods, and always be a source of perplexity and expense in keeping it in repair. Two plans have occurred to me, in which this difficulty can be avoided. The first is, by converting the present guard lock into a lift lock, dispense with one of the combined locks, and make a canal from the foot of the combined locks along the river bank to the above mentioned place, and lock down into the river by a lock of seven feet lift. The second plan is, to lock into the river from the level above the combined locks, by two locks of seven feet lift each. In either of the above plans, I would propose to take the water in to supply the canal, through a sluice below the guard locks. I do not think that a connection can be made with the Pennsylvania canal, without a stipulation to that ef |