Is it justifiable, except in a very extreme case, to unite those two disadvantages, such a length of tunnel with that inclination ?—I think nothing but an overruling necessity could justify it. from near the foot of London Bridge on all houses. Over two made into two five. the transverse section of the tunnel ought to viaduct 22 feet high, supported by about room private houses, I have been, and be greater on a slope than on a level in the 1000 arches, to Deptford and Greenwich. must confess, contrary to my expectations, proportion of 30 to 9. In so short a distance as 4 miles, great dif- found them comfortable, roomy, and Mr. Joy.-Your attention has been callferences in the under soil were hardly to be compact. The inconvenience I antici-ed to railways in various parts of the world; expected. However, substrata of clay,ated in any former communication from do you know of any parallel to this, uniting gravel, sand, peat,. bog, and floating land, smoke, is removed by the use of gas stoves, the length of this tunnel with that inclinaseem to have presented themselves in luxu- with which the houses are furnished. Intion ?-No, I am not aware of any. riant variety, the best soil often in juxta-posi-the neighborhood of London many of tion with the worst. But with these the en- these arches will doubtless be let for of gineer has successfully contended, so that fices, vaults, and warehouses. I have it would require a professional eye to dis- heard that 500% per annum have already cover any effect of settlement out of 575 been offered for some between Joinerarches already built.* In general, the arches street, and the bridge terminus. At all Have you considered the different modes are segments of circles; but almost every events, it will be the managers' fault if proposed for working that tunnel; additionspecies of arch in use, except the Gothic, is ultimately they do not turn in a large real locomotive power or a stationary power, pressed into service as circumstances need. venue. It is said there will be about 1000 either by an endless rope or a single rope? The eye is occasionally arrested by an arch of them, which some calculate will fetch Yes. commencing with the segment of a circle, 30l. per annum each; or, on the whole, a Have you also considered it as worked and when looked through, presenting a para- rental of near 30,000l. per annum. But partly by the one and partly by the other?bola or part of an ellipse. Professional suppose only 900 of them let, and at 20%. Yes; it might be worked partly by one and men well know the difficulties of such ob- each, the rental will be 18,000l. per annum. partly by the other; the tunnel is not the lique structures, yet, as far as I could per- or 2,000l. annually more than the interest same length as the slope; the slope is two ceive, there was no deficiency of symmetry of the whole capital (400,0007.) at 4 per miles and a half, and the tunnel a mile and or regularity, while the transition of figures cent.; a tolerable argument that the en-three quarters in length; it might be worked seized the mind with its pleasing effects.-gineer had here good reason for preferring The prevailing character of the work may his viaduct to a profitless embankment. be summed up in uniform neatness and strength without heaviness. cross walls are built between the arches, The following evidence of Dr. Lardner For the purpose of additional security, on the "Great Western Railway Bill," will over which the rails are to lie for the trains, be found to contain many items of interest and the intervals are filled with concrete.—and amusement to our readers. By this means the mass is rendered one solid piece, and the weight of the carriages is spread over a large space. It seems to be a favorite maxim with Colonel Landmann, the engineer, that wherever the lead is long, a viaduct is generally more economical than an embankment. Without implicitly subscribing to this doctrine, in which there is often more truth than some civil engineers are willing to admit, it is evident that em. bankment in the Greenwich Railway would have been little short of insanity. Putting out of the question the enormous expense of forming it where all the materials have to be raised to the embankment, not to be drawn out on a level, and of the additional ground to be purchased, both for the embankment and materials; setting, I repeat, all this aside, together with the immense rental which must ultimately result from nearly 1,000 manufactories, shops, houses, and warehouses, into which the arches are being converted, it is probable that long before such an em. bankment of 22 feet high could settle into a road fit for locomotive travelling, the Colonel's viaduct will be finished, and likely enough return a large portion of the capital expended. At the Deptford end several of the arches are now occupied by the Compa. ny for smiths', carpenters', and other shops, which must obviously be a great saving to the concern. One or two of the arches are also tenanted as public Lest my friend Sir John Rennie should again haz ard an expression that I am "unacquainted with the engineering details," I must here beg to observe, that a few of the piers on each side of the abutments support ing the elliptic arch over Ear's sewer, nod a little towards the sewer, from a circumstance of which it is unnecessary to go into the "engineering details," but I will if Sir John wishes it. by a rope through the tunnel. First, as worked by locomotive engines, what would there be its great objection?—I think I have stated its great objection already; the probable difficulty attending the destruction of air by the fire; and in considering that it appears to me that it ought to be considered, not so much with regard We suspect that some of the learned Doctor's opinions on the question of rail- to the health or life of the passengers-I do to the positive injury that may be produced road "inclines," will not receive a very rea- not think there would be any-but with redy assent from many of our civil engineers.gard to the unpleasantness and inconvenHowever, the whole is worth a perusal ; and ience arising from the existence of a quanif the parts of the examination in relation to tity of noxious vapor through which they would be carried. "noxious air," do not excite a smile, our readers must be of different material from ourselves. We shall continue it in our next. From the London Mechanics' Magazine: That is an objection more or less applicable to tunnels upon a level?-Less appli cable to them, because there would be less power requisite. Would the atmosphere of the tunnel be injuriously affected and impregnated with the gases produced by the combustion ?Not injuriously, but inconveniently, I think. In the same proportion as the increase of power?-Yes. On the Great Western Railway Bill, 31 of August, 1835. You have stated that there would be so The Earl of RADNOR in the Chair. much greater power required, and that reDIONYSIUS LARDNER, LL. D., being ex-quiring a greater proportionate quantity of amined, gave evidence as follows; combustion, that the ill effects would be You have heard a good deal said in ex-produced in that proportion. What would tenuation of the Box tunnel; what is your be the proportion of increase in the conopinion upon that subject?-The combina-sumption of fuel?-As 30 to 9. tion of a tunnel with a slope appears to be the objection to it; and the power requisite to pull a load up a slope of 1 in 107 is greater Mr. Joy.-Would there be as much air than the power necessary to pull the same consumed in that tunnel as in a tunnel on a load on a level in the proportion of 30 to 9. level of five miles and four-fifths long?In round numbers, nearly 3 1-2 to 1?-Yes, nearly. The length of the tunnel Yes; it requires 9 lbs. per ton to pull a would be in the proportion of 30 to 9; there load on a level line, and it requires 30 lbs. would be as much air consumed in this tunto pull it up 1 in 107. nel as there would be in a level tunnel longer in the proportion of 30 to 9. Do you think any method of ventilation could be attainable that would render it otherwise than almost intolerable?—I scarcely think that the common mode by shafts would Applying your attention to the question of the tunnel, in what way is that difficulty aggravated beyond the mere proportion of the greater power required?-The increased power necessary for a slope must be produced by a proportionably increased con- do it. sumption of fuel; that will produce a pro- I have asked you whether it was actually portionably increased destruction of atmos-practicable; is it not a feature devoutly to pheric air; and, of course, if the tunnel be be avoided?-Yes. intended to be kept as pure on the slope as it would be necessary to keep it on a level,Yes. To be avoided at almost all hazards? Would it be an eligible thing, such a tun- The degree of injury, if any there be, || seven inch rope would be six pounds and a nel in the course of a line, or almost intole-must depend upon the proportion?—Yes. half per yard. rable?-I think it could be justified only by It may be diluted with common air, so as What would be the total weight produced? overruling necessity. not to be fatal to life or health?—Yes, there -The total weight of that endless rope is always a quantity in the air. would be about 57,000 pounds. Mr. Joy.-Is this grievance much the same, or very materially aggravated, by such a tunnel and such an inclination being in the middle of the line rather than at the extremity?—Yes, it is more objectionable than at the extremity. Why? Because of the unpleasantness, and the interruption to the transit of the trains when the passengers are in them; you come to a stand-still; they must undergo a change in the moving power, and a similar change takes place at the top. At the end, if there is a tunnel, passengers hardly consider they have started until they have already passed through the tunnel; that is the case upon the Liverpool line, where there is a short tunnel at starting; no one could have travelled that line without feeling that had that tunnel occurred at Rain-hill instead of wher it is, it would have been felt a much greater inconvenience, though the absolute loss of time might not be more. Supposing Mr. Brunel shall have said, in answer to a question as to the danger of the atmosphere being rendered noxious by the passage of the engines, "I think not; there is one in existence upwards of a mile, and another on the Birmingham line;" and again, when asked, "Is the inclination so steep?" if he should have said, "It will not affect the atmosphere," is that correct or erroneous?-I think Mr. Brunel is in error there; it would affect the atmosphere. If the extra power is supplied by a sta- How long?-About five miles. tionary engine, the consumption of fuel Mr. Joy.-Calculating the friction of would not be greater in the tunnel?—No. such a rope thus worked at about a twelfth Mr. Joy.-Have you made calculations of its weight, which was the proportion given of the proportions of these gases?—Yes; by Mr. Stephenson and Mr. Locke, what of the proportions of foul air to be produced. pull would it require to work a train of fiftyWithout troubling you to go into it in two tons ?-To propel fifty-two tons upon a any detail, could you tell us the different slope of 1 in 107 will require for its gravity gases you think injurious; the round suma 107th part; you are to divide the 52 by of them produced in the passage through 107, and you will get the power of draught this immediate tunnel, for a load of 100 necessary to overcome the gravity of the tons in a tunnel of a mile and three quar-load. ters long, upon a slope of 1 in 107? Have What would that be?-1,088 lbs. ; then you calculated the quantity of noxious gas there wonld be the friction of the load, which that would probably be made?—Yes; the is at the rate of 9 lbs. per ton, which for total quantity, taking for granted that it fifty-two tons, 468 lbs.; these two together takes half a pound of coke per ton per mile would come to 1,556 lbs.; that is exclusive upon a level to draw a train, which, I be- of the rope. Then the experiments of Mr. lieve, is in practice nearly the case, the Stephenson and Mr. Locke on the friction quantity of noxious gas produced in this of the rope show us, that the friction may tunnel would be something less than 4,000 be taken at about a twelfth part of the weight lbs. weight, with a load of 100 tons. of the rope; and those experiments appear Every time a train goes through ?—Yes. to me to be very satisfactory and conclusive; Mr. Joy.-Does any objection exist with there was an average of several taken, and regard to the assistant engine on the Man-they have given very nearly the same result; chester and Liverpool line; they have one and taking one-twelfth part of 57,000 lbs. there?—Yes; not in a tunnel. you will get the force necessary to pull the rope, which alone is 4,752 lbs.; the load therefore would require 1,556 lbs., and the rope 4,752 lbs., making a total of 6,308 lbs. Is not the result of this calculation, that it would require about three times the pow I am speaking of the inclination; is there not an inclination on that line very near this?—Yes; 1 in 96. Is there any practical inconvenience there, as you have observed the line so fre In point of fact, is it not true that there|quently, with reference to the additional en-er for the rope, compared with the load? will be an additional difficulty, as to the ventilation, from the increased power that will be requisite ?—It will require more ventilation in the proportion of 30 to 9. If it is assumed by the engineers on the other side, there will not be more ventilation required than on a level, that is an oversight, in your judgment?—Yes, that is an oversight, I suppose. ། Supposing coke used instead of coal, would not the gas produced be more noxious?—No, not more noxious; it is the same gas; the combustion of coke produces carbonic acid gas, sulphurous acid, and azote. Coal would be quite inadmissible. Mr. Joy.-Would not the gas that wou'd escape from coke be of a more injurious nature if it existed in any quantity?—Yes; it is not only gas that escapes from the combustion of the coke, but the gas that is decomposed in the atmosphere would be more injurious. Would not this gas, unless it found a vent in a heated state, be likely to remain? -Yes, from its specific gravity: it is half as heavy again as the atmospheric air; the carbonic acid gas. That is the offensive gas of which you speak?-Yes, the gases are mixed together, and if they cool they are heavier than the atmosphere, and apt to remain. upon The mischief must very much depend the quantity; is not the carbonic acid gas what the miners call choke damp, in a great degree? Yes, it is what exists in wells and in the Grotto Del Cane. If it is an excessive quantity, it is fatal to life?—Yes. gine?-The additional engine is not always Have they sometimes to wait from its Have you known trains come to a dead stop on that inclined plane ?—Yes; I have been upon it more than once when that has happened. Have you had to wait a considerable time?—Yes, until the engine could be got. Would the extra cost necessary for keeping this engine ready for use be another objection?-Yes; they would be always obliged to keep it ready for use, whether wanted or not. I will call your attention to another mode At the rate of about ten miles an hour?- Yes; for a load of fifty-two tons it is in the proportion of 15 to 47, very nearly. To move that at the rate of fifteen miles an hour would require what power as expressed in horses?-Twenty-five pounds pulled at the rate of fifteen miles an hour is equal to one-horse power, and therefore 6,300 lbs. pulled at that rate, would be equal to 252 horse power. Have you a corroboration of that result from the proposed engine on the tunnel now making on the Liverpool and Manchester railway?-The tunnel for passengers is a tunnel of a mile long, I think. What is the power of the engine there proposed?-It is, they say, 140-horse power. That is for passengers only?—Yes, for light loads. What is the declivity there ?-1 in 100. Very nearly the same as here?—Yes. Mr. Joy.-Is that consistent with the calculation you have just been giving to the Committee?—Yes, it agrees very nearly with it, as nearly as possible. I should state it would be necessary to have two engines, one to work while the other is accidentally deranged or repairing, otherwise the whole traffic upon the road will be stopped; there must be a pair of engines. May not that be estimated at a lower tonnage in consequence of its being intended for passengers only?-Fifty tons is the amount of an ordinary load of passengers, What sort of rope would the Box tunnel What would be the weight of a seven inch Is not that about half the length of the Box tunnel?-Yes, it is about a mile long. Is it correct to suppose that a five and a "half inch rope would be sufficient for the Box tunnel, because the incline is flatter||quire a small locomotive in consequence of Would not there be some objection to that gives at all a sufficient explanation of the practicability of stopping such trains as would usually go on such a line as this; upon such an inclination as the Box plane ?—No; because the power of the break is inversely as the load; and though you might stop a wagon loaded with five persons (I believe the average weight of a man is 150 lbs., which would be 750 lbs. plus the weight of the wagon), though it might be easy to stop that with a break, it would require a greater power by the break to stop it with a greater load-a power greater in proportion to the Would the calculation of the sufficiency of rope, a five and a half inch rope, be conclusive if it was applied to so much shorter a line?-No; the acclivity has nothing whatever to do with the calculation; an end- Is the original cost of such a rope heavy? less rope, which would be sufficient for a-Yes. certain load on one inclination, would be Is the wear and the tear considerable ?-load. You cannot infer much from that exsufficient for any other inclination; the weight of the rope has nothing to do with it; it balances itself. Yes. Has it to be often spliced ?—Yes; the rope on the Liverpool tunnel is spliced twice a week, I believe. Are the sheaves and the pulleys that the rope runs upon likely to break and get out of order?—Yes. In order to arrive at a proper conclusion, is itnot necessary to take into account the greater length of the line?--Yes, and that alone. And not the steepness?-Not when it is an endless rope; a single rope would re- What is the number of those pulleys in a quire steepness to be taken into considera-mile ?-220 in a mile, I think. tion, but not an endless rope. At the tunnel in question, on the Liverpool and Manchester line, is not the load of the locomotive divided into five or six different portions, and drawn up at five or six different times?—Yes; it is drawn up in loads of twenty-five tons; this would not do in the middle of a line. Do you know any thing of the cost of those pulleys?-From 15s. to 20s. is the cost, where less power is used. Would not this mode require about three times the power usually expended?--Yes; I should say in the proportion of 15 to 47 by an endless rope. I am speaking of a single rope?—There would be less waste of power in a single rope, but we must take into account the power to carry it back. Would it not come nearly to what I have stated ?—I have not calculated that. periment. Supposing the carriages to start from the top of the plane in a state of absolute rest, what resistance would be required in order to limit its speed to 30 miles an hour?-It will be the resistance of the same number of pounds per ton, whatever be the limit of the velocity. The circumstances will be these: a train descending a slope of 1 in 107 has a downward tendency, which would be balanced by 12 lbs. per ton; and, of course, whatever the velocity you want to restrict the train to, the break should exert a retarding force, amounting to 12 lbs. per ton. Taking those data, what resistanee would it be necessary to exert through a distance of two miles and a half, 7,588 feet?-To Is it comparatively unimportant at the limit the velocity to 30 miles an hour, supend?-If the load was to be drawn up in posing it to begin from a state of rest, the that way in portions in the middle of the trains starting from a state of rest at the line, the line would be occupied a considetop, and being allowed to proceed by gravirable time, and the trains of passengers ty only, without power, would acquire a vewould be stopped until all this business of Have you any objection to stationary locity of 30 miles an hour after passing over carrying up the loads was finished; and power in the midst of a line like the Great 5,612 feet. Then supposing the break to even at the end of the line, unless the slope || Western?—Yes; there is an objection to it be applied, so as to check any further inwas exclusively devoted to goods, it would in the interruption it would occasion in the crease of velocity, it must exert a force of not do there. rapid transit of passengers and the change of 12 lbs. per ton in order to do that, and that power; those are sufficient objections to it. force must be exerted through the remainWhat would be the sort of power neces-der of the slope, which would be 7,588 feet; and the total force would be equiva lent to 4,500,000 lbs., raised a foot high. If a load of 100 tons were to arrive at the top of such an inclination, there would be a waste of time in the arrangements necessary to draw up a single rope?—It would be sary to divide it?—It would be divided into four, and then one would be drawn up, and then another. Whereas 100 tons can be very easily moved upon other parts of the line?-Yes. Do you happen to know whether the elder Mr. Stephenson asserts that an endless rope of five miles long is impracticable?—Yes, I recollect he says that. You consider it, in common parlance, impracticable?-Ycs. pulled back by an engine attached to the end Mr. Joy is heard in answer to the obser vation. I need hardly ask you whether the increased velocity you have spoken of would not then be much more dangerous?—The velocity would be much more increased if it broke loose from the break. Do you agree with him?-Yes, it is within the bounds of mechanical possibility I think, but in the common sense of the word it is impracticable; I hardly think any one would attempt it. Mr. Joy.-Leaving both the endless rope Have you any idea that it would be adopt-and the single rope, I wish to call your ated?-No; the power expended upon the tention to the breaks. There was an exrope would be so preposterously great com- periment stated by Mr. Brunel on the Can- If Mr. George Stephenson should have pared to the load to be drawn. terbury and Whitstable inclined plane. Is stated that the break often fails to act; is he that applicable to the Box tunnel? Suppos- correct in that?—Yes; I have seen it freing it to be stated by Mr. Brunel, with re-quently fail on the slopes on the Manchester ference to the Canterbury and Whitstable Railway. Railway, "I have been down that plane twice, without a rope in the carraige, alone, with nothing but a break to check the carriage, and allowing it to run all its full velocity; by the break it was stopped in sixty yards.-How many passengers were there in the carriage? We were five only; of Do you consider, speaking of a single course, I did not try an experiment of that rope, it would be but half the length ?-Yes. sort with many passengers.-Was it fully Two miles and a half; would not that re-loaded? No." I would ask you whether Now turn to the single rope. Suppose it is to be worked by a single rope, is it one of the objections necessarily involved in a single rope, that there must be a small locomotive to draw it back?-There must be some means to draw it back again, and the weight is so considerable that the power must be considerable. Did you ever find that inconvenience yourself when making experiments on that Railway?—Yes. On an inclined plane of 1 in 96?—Yes; I have seen it totally fail with a train of goods; it was burnt; the friction burnt it. Just state the particulars of that?—I was descending the slope of 1 in 96 on the Manchester Railway, with a train of goods; the engineer let the train run down for a consid erable time without the break, and we ob-quired it is not, but if all precautions are ty acquired at the foot would be fifty-four miles an hour. If Mr. Locke should represent that to be not accompanied with danger, must not it have been in consequence of previous pre. Is it not objectionable that there should cautions specially taken on the occasion?— be such a curve at the bottom of an inclined || Yes, oh certainly; because accidents have plane?—Yes; it would be better further off. happened where the trains have broken loose Though a quarter of a mile is sufficient in that tunnel, and the wagons have been for the expenditure of the common power, all smashed to pieces. is it not insufficient for the expenditure of the dangerous power acquired by that increased velocity?—Yes, it would be. In your judgment, supposing the train to Do you know what the velocity was?-Ibe worked by a single rope, and such rope can only conjecture that it was something were to break, would there not be great very great; I should say from forty to fifty danger?-There would be danger arising miles an hour. from the train being precipitated down. Have you ever had any other misfourtune of the same kind in a curve?—Yes, I did; I recollect an instance of it in a curve or bend in the line; that was not on a slope; it was nearly level. Is there to some extent a natural tendency for the engines to get off the rails produced by the centrifugal force upon such a curve as that you have mentioned ?-Yes, there is; and for that reason curves are inadmissible, except with a very large radius. When a body is moved in a circle it has a tendency to fly from the centre, and this tendency in If it is the opinion of Mr. Prunel, that the case of trains on a railway presses the there would be no great danger if the rope wagons against the outside of the curve, broke and that the slightest resistance of the and gives them a tendency to run over the break would stop it dead, is not that erro-rail on the convex side of the curve. neous?-I do not agree in that at all; I do not think any resistance would stop a train dead; it would gradually stop it. Mr. Brunel says he has not calculated the amount of velocity that would be acquired; have you calculated the amount of velocity acquired in falling down these slopes?—Yes. State the circumstances?-I was proceeding from Liverpool to Manchester with a train of passengers, and at a bend in the line, where, from the flexure of the road, the engineer could not see a great distance before him, it happened that a train of stone wagons was occupying the road in advance; a signal was made to the engi- Just state what it is without any break?neer by the road police to cut off the A carriage or train, commencing from the steam and put the breaks on to retard it; top of the Box Hill Incline, from a state of and he alleged that he did so; but the velo-absolute repose, supposing it not to be procity continued to be so great, notwithstand-pelled by any power, would at the foot of ing the breaks, that we came against the the slope have a velocity of forty-six miles train of stone wagons, and smashed them all an hour by gravity only, and the time of deto pieces; the wagons were broken all to scent would be six minutes and a half. I pieces, and the stones thrown about, and the omit the small fractions. framing of the engine, though of strong iron, was broken. Did you knock the stone carriages to pieces? Yes. We were protected by the engine and the springs; some of the passengers were bruised a good deal. There are provisions made in the carriages that carry passengers to protect them from the effects of collision, but there are none in the case of stone wagons. Was this upon an embankment or a cutting ?-It took place in a cutting quite sufficient to hide the wagons. What is the length of the radius of the curve where this accident took place?-It is a very considerable radius. Mr. Joy.-Do you know the radius at the bottom of Box Hill?-It is stated to be three quarters of a mile. If you were in a cutting would not that aggravate the difficulty, as you would not see the wagons before you ?-Yes, it would. What is the distance of the curve from the end of the Box Plane?-I believe it is stated to be a quarter of a mile. That is allowing the friction of nine pounds a ton?-Yes, it is. That is assuming the train to descend with any power whatever, and to commence from a state of rest?—Yes; and if it does not commence in a state of rest, you must add to the forty-six miles an hour the velocity that it had at the beginning. If it was starting at the rate of twenty miles, it would get up to sixty-six ?-Yes. Would not that be perfectly serious and formidable?-That is a matter of opinion; I am not afraid of those high velocities if the road be straight and level; but the curve which takes place in a quarter of a mile from the end of the plane would render it quite objectionable. Quite formidable and dangerous?—Yes. There would not be sufficient space in that quarter of a mile to correct such extreme velocity?-No, nothing like it. Does not that tendency increase in the same proportion as the square of the speed and the smallness of the radius ?—Yes. Have you calculated the effect of this curve, and the lateral tendency to run off the rails which this speed will produce?— Ycs; it is a matter of very easy calculation. First tell us with a speed of fifty miles an hour and a load of 100 tons?—The outward tendency would amount to 93 lbs. a ton; that would be 9,300 lbs. altogether; that is, with three quarters of a mile radius. At forty miles an hour?-57 lbs. per ton; that would be 5,700 lbs. altogether. At thirty-five miles an hour?-47 lbs. per ton; 4,700 lbs. At thirty miles an hour?-33 lbs. or 3,300 lbs. These different aggregates of outward pressure would be divided equally among all the parts of the train, and would not apply to any one part?—It would apply at so much per ton, according to the weight of the wagons; if the wagon was loaded with five tons, then the outward tendency would be five times 93 lbs. Upon that wagon ?--Yes. If they were divided in a space of five feet, each one of those five feet would bear a proportion?-No, it is on the flange of the wheel; it would be divided between the two flanges of the two outward wheels, and the two outward wheels would be pressed outward with the force I allude to; each would be pressed with half the weight I have stated. If there were ten wagons, each wagon would have a tenth of the whole; and if there were four wheels to each wagon, that tenth would be divided between the four wheels of each of those wagons?—No; it fected, and it is divided between them Mr. Joy. Suppose it is contended that the danger was reduced to nothing almost, because it was in cutting?-The difference only would be this, that if they were thrown In your judgment, is it sufficient to pre-off the rails, they would not be thrown over is only the two outward wheels that are afvent any injury at that distance ?-There an embankment, but against the side of the will be great danger of having undue veloci-cutting; there would be a difference of re-equally. ty; and on arriving at the curve, if the break should fail, the engine would arrive at the curve with very considerable speed. A quarter of a mile would make very little abatement. sult likely to arise, but not a diminution of Mr. Joy.-Does not it follow from what you have stated, that a very slight addition Mr. Locke states he descended the tun- would tend to throw the wheels off the rails? nel on the Liverpool and Manchester when-Yes; a very slight pressure with that the break was not applied at all; have you tendency would help them over the rails. If it should be contended that a quarter calculated what must be the speed there? At the junction of two rails they are very of a mile is sufficient to obviate any aggra--Supposing the wagon to descend from a seldom flush. After they have been workvated inconvenience from the velocity, is state of rest at the top of the tunnel (I speaked a little time one gets a little lower than that correct?—If accidental velocity be ac-"of the tunnel for goods, 1 in 48,) the veloci-" the other, and the wheel coming against the What should you consider undue velocity? -Fifty miles an hour I should consider undue velocity. corner with that pressure would give it a most of the manufactories in this country || weight of nitre. They are placed in a tendency to go over. and England. shallow vessel of earthenware or cast-iron, In your judgment, would not the danger Rationale. When nitrous oxide (deutos-mounted on a wheel carriage, and, after of such a curve be extreme with respect to ide of nitrogen) and sulphurous acid are in being ignited, are shoved in through the passenger trains from Bath to London?troduced together into the same receiver, door, which is shut after them. When Yes; I think it would be dangerous, in a hey mix without any chemical action upon he combustion is completed, and the acid train acquiring undue velocity, in descend-each other; but if oxygen be present, ni rous condensed in the water, the carriage is ing the slope at Box Hill. acid gas is at once formed, whose presence withdrawn, the residuum taken out of the. will be manifested by a quantity of red funes. vessel; it is then charged with a fresh This last named gas will also remain un- quantity of the mixed materials, and reacted upon by the sulphurous acid, unless introduced after they have been ignited. Would you consider 30 miles undue ve- they be also mingled with the vapor of wa- These successive combustions are conlocity?--I consider it is objectionable. ter. But when this vapor is mixed with tinued until the liquid at the bottom of the Mr. Joy. If the Lowther Arcade has them, the red vapors gradually disappear, chamber acquires a density of 1.375 to been alluded to as an illustration with refer-and a white crystaline solid is deposited on 1.5.* Beyond the latter limit, condensa ence to this tunnel, it must be considered as the sides of the receiver. These crys.tion is unprofitable, because the attraction oncfined only to its similarity in point of tals are a compound of sulphuric acid, ni. steepness?-To its appearance; slopes up-tric acids and water. This crystaline on Railways have a tendency to remove the substance is highly deliquescent, so that appearance of danger, and to create its re-if the bottom of the receiver is covered ality. with water, they fall into it and dissolve What do you mean by slopes upon Rail-with a slight effervescence; the water be. ways?-I mean inclines; an incline, that comes charged with sulphuric acid, nitric has no appearance of danger when you look oxide is evolved, and in coming into con at it, may have a great deal of real danger in tact with oxygen is again converted into it, though that inclination is one that willitrous acid gas. It is only necessary to not be perceived by the eye. supply a new quantity of sulphurous acid, and the formation of the solid substance may be again repeated, and an additional quantity of sulphuric acid obtained. Do you mean to say that an inclination that does not appear to be dangerous to the eye may be so in point of fact? Yes, there are slopes on Railways which, while they do It is therefore obvious, that sulphuric not appear to have any danger whatever in acid may be formed by burning sulphur their appearance, have a great deal in reali-in a chamber whose floor is covered with ty; it would not apply to such a slope as 1 in 1,000. But some, which are nearly imperceptible, are very dangerous?—Yes. (To be continued.) Applications of Chemistry to the Useful Arts, being the substance of a Course of Lectures delivered in Columbia College, New-York, by James Renwick, Professor of Natural Experimental Philosophy and Chemistry. I. ACIDS OF COMMERCE. 1. SULPHURIC ACID. AUTHORITIES.-PARKES. Chemical Essays. of the acidulated liquor for the sulphuric acid diminishes, and nitrous acid gas be. gins to be dissolved by it. This gas is separated with difficulty, and impairs the useful qualities of the acid. The liquor having reached the above degree of concentration in the chambers, is removed from them to leaden boilers, where, by the aid of heat, it is further concentrated to 1.7t. Beyond this the concentration cannot be carried in a leaden vessel, for fear of melting the metal. The acid liquor is therefore next placed in close retorts. These were originally, and are still, in most manufactories, made of glass, and set in an iron sand bath; in them the acid is brought, by the evapora water, and into which nitric oxide is in-tion of the water in which it had been controduced in any manner whatsoever, for densed, to the specific gravity of 1.84. the combustion of the sulphur will furnish This is the greatest strength of the acid of sulphurous acid, and the spontaneous evap-commerce, and is sufficient for all practical oration of the water the quantity of its purposes. vapor which is necessary. Nitric oxide may be furnished by the action of burning sulphur upon nitre. And on this fact the most usual process de pends. It may also be obtained by the action of sugar or of starch upon nitric acid. On the latter fact the new and improved process is founded. Glass retorts are liable to frequent breakage, in consequence of the violent agitation with which the separation of the bubbles of steam from the acid is attended. The size of the bubbles may be lessened, and he risk of breaking duminished by the introduction of angular fragments of glass, or strips of platinum, into the retort. But it would be far better to employ, as has been done in some French establishments, retorts of platinum. The only objection to ese is their original cost, but when a sufficient capital can be obtained, the cost of the acid is lessened by employing them. Manufacture by a mixture of Sulphur and Nitre. The chambers in which sulphuric acid is manufactured are made of sheet lead. They are of a rectangular shape. DUMAS. Chimic appliquée aux arts. The bottom is raised about six feet from History-Sulphuric acid was originally the ground, and supported by stone flags; prepared by the distillation of the sulphate the sides and top are sustained by a An improvement in this process was ef of iron, in a mode that we shall have occa wooden frame, and a space of about six fected by Chaptal, who succeeded in masion to mention, as still used in manufac-feet is left between this frame and the walls king the action of the chambers perpetual, turing it for a special use. As this sulphate and roof of the building which contains instead of intermitting, by burning the mixwas known by the name of green vitriol, the it. The separate sheets of lead are care. ture of sulphur and nitre in a separate furacid was called oil of vitriol. It was after fully soldered together, and are united to nace, directing the current of gases evolved wards discovered that the combustion of the frame by clamps of lead soldered to from it through the chamber by means of sulphur under vessels moistened with water, their outer surface. flues, and forming a draught by means of produced the same result. Finally, after Single chambers have been constructed a chimney. This method is attended with the reception of the modern theory of che-of all dimensions, from 5,000 to 100,000 difficulties and a risk of loss, if not carefully mistry, Lefevre and Demerey conceived that cubic feet, and they have been made of managed; but, when well conducted, it the oxidation of the sulphur might be pro- smaller size, but so arranged as to com- gives a larger quantity of acid than the othmoted by mixing it with nitre, a salt whose municate with each other. It does not er. The first described me hod yielded, in acid is easily decomposed. Their experiment appear that the exact shape and dimen. its carlier stages, no more than 150 pts. for fulfilled their expectations, although their sins which are most favorable have 100 pts. of sulphur. As it ought to proview of the rationale is now known to be vet been discovered. At any rate, a quan. duce 318 pts. of acid at 1.84, more than erroneous. The operation was at first per-tity of sulphuric acid proportioned to the one half is lost. By more careful manageformed in large glass vessels, but as these are sulphur consumed has never been obtainment, the product has been raised to 240 expensive, leaden chambers were substituted. A bed of water a few inches in depth pts., but the method of Chaptal has yielded ed, and finally when the several steps of is spread over the floor of the chamber. 300, involving a loss of no more than 6 chemical action which occur in the process Inmediately above this, a door, covered per cent. To give it this superiority, it is were investigated,,a method was discovered with lead, is placed, by which the matein which the use of nitre might be dispensed rials are introduced. These are sulphur with. Nitre is however still employed in mixed with not less than one-eighth of its * 40° to 50° of Beaume's hydrometer. † 60° of Beaume. 1660 of Beaum |