snpposing the 337-5 tons on board in the shape of CARGO (paying a heavy freight), the velocity would be

an increase of 0.82 mile per hour by the superior power of the oscillating engine alone.

But this comparison is faulty, because we have not accounted for the decreased weight of 337.5 tons.

From the magnitude of these ships, each inch of their immersion will be equal to about 20 tons. Therefore

decrease in the draft, so that the area of the midship section will be reduced by the lighter but more efficient machinery, from 670 to 614 feet; and using the same formula we shall have

or an excess over the beam engine of (14.31-13-08)=1-23 miles per hour.

I take from an original prospectus of the Royal Mail Company the route out and home at 10,500 statute miles, and though perhaps not absolutely correct, it will answer my purpose for an illustration of the advantages to be derived from improved machinery.

The beam engine will produce a velocity of 13.08 miles per hour-the oscillating engine, 14.13 miles (all things being the same). Therefore, this service would be performed by the former in 33 days, and by the latter in 30 days; and this saving of three days would be accompanied by the insurance fund of 37,500l. !

On the other hand, presuming that a cargo of 337-5 tons were taken on board, the voyage could be completed in 314 days,-a saving of two days, and the freight of the 337 tons of merchandise, which I leave others to set a value upon.

Applying these views and arguments to the Cunard's line of steamers, it is certain that if an average passage is now 11 days, it would become one of 9 or 10 days at the most.

I may, perhaps, not be fully understood by your general readers; but I recommend this paper to the careful consideration of the profession, and to that of the powerful companies interested in the matter here discussed. You, Sir, know I have no trade-interest in what I write-I am not “looking for a job"-but do not wish to see the day when our pre-eminence as engineers can be called into question.

It would be a curious finale, if our brethren in America (far-seeing as they are) were to adopt the improvements now suggested. I believe that will be the result; and if they do, our boasted performances, as they now exist in ocean steam navigation will be entirely eclipsed.

I am, sir, yours, &c.,

PRESSURE, NOT PUFF.

48

Translated for the Journal of the Franklin Institute.

On the Distillation of Mercury by Overheated Steam. By M. VIOLETTE. The new process for the distillation of mercury consists in plunging the mass to be distilled into a current of steam overheated to the temperature of 350° to 400° Cent. (662° to 752° Fahr.) The vapor acts both as a calorific and a mechanical agent; it, in the first place, heats the metal, so as to excite distillation, and then drives before it, and draws over the mercurial vapors, whose renewal it also facilitates; it hastens the distillation, as a current of hot air facilitates the evaporation of water; the steam charged with mercurial vapors are condensed together in a common refrigerant; the metal separates and sinks to the bottom of the vessel, while the condensed water flows out at the top. It is a rather curious thing to observe the liquid stream which flows from the refrigerant; two currents or streams may be distinguished, the upper one water, and below it the mercury; it is a continual current of each substance. No concussions are produced, and the operation goes on as tranquilly and easily as in the case of the distillation of common water.

The apparatus which served me in all my experiments was composed, first, of a cylindrical cast iron retort, which receives the recipient which contains the mercury; second, of a wrought iron worm in the upper part of the furnace which heats it. The steam circulates in the worm, is there heated to the proper degree, enters the retort, traverses it from one extremity to the other, passing over the surface of the mercury, and escapes with the mercurial vapors, to condense with the water and the mercury in the refrigerant.

In a series of tables, the author gives the results which he obtained in a series of experiments on the distillation of mercury alone or amalgamated; he indicates the quantities of steam necessary, and exhibits the economical advantages, which he sums up as follows, viz:

1. Facility of the Operation.-The boiling and distillation of water are substituted for the difficult and dangerous boiling and distillation of mercury; no more trouble in the management of the fire, no more danger of breaking the apparatus, no more difficulty in getting out the metal, no more notable destruction of the retort; a constant and determined temperature, much lower than the red-heat usually employed.

2. Economy of Labor.-A single laborer may manage a distillatory apparatus charged with 1000 kilogrammes of amalgam-the new process permits the largest dimensions.

3. Economy of Fuel.-This is certain, and practice alone can determine the amount. There will be no useless excess of fuel expended, since the apparatus will not be heated beyond the temperature necessary for the distillation of the metal.

4. Economy of Mercury.-The distillation of 100 parts of the amalgam of silver determines a loss of 2 parts of mercury. There are annually produced and distilled 6,000,000 kilogrammes of the silver amalgam this is then a loss of 120,000 kilogrammes of mercury, worth at least 1,000,000 francs, ($200,000,) which this new process permits us to avoid.

5. Public Salubrity.-In the new process there is no loss of mercury;

the mercurial vapors are extinguished in the steam, and are condensed with it; moreover, in the common mode, the mercurial vapor still fills the whole apparatus, when this is opened at the end of the operation, and spreads into the air, while, in this latter method, the steam sweeps out all the metallic vapor from the apparatus, and the opening of it is without danger. The guarantee is thus complete, and the employment of overheated steam appears to have solved the problem which has been long sought after, to preserve completely the workmen from the mortal attacks of the mercury in the numerous and important branches of industry in which the distillation of this metal is required.-Comptes Rendus de l'Acad. des Sci.,. Oct. 14, 1850.

For the Journal of the Franklin Institute.

On Vertical and Radial Paddle Wheels.

The last four numbers of the Journal have contained several articles from Mr. Isherwood, one of the Chief Engineers of the U. S. Navy, advocating strongly the great advantages which, he contends, vertical paddle wheels have over the ordinary radial paddle, and a reply to Mr. I.'s first article by "M." who takes the opposite side of the question, and the one most generally received in England, where the wheel of Morgan is best known and understood. Without entering into any discussion as to the merits of the two wheels, and willing to leave the matter in the hands of those whose interest it is to have the best-the commercial communityI propose to examine some of the calculations and assertions of Mr. I., and see if they are worth as much as he would wish them to pass current for, and in his last article insists we shall take them at.

Mr. I. compares two vessels of 600 and 900 tons, and, without knowing the pressure on the piston, assumes it to be the same in each, because the pressure in the boiler was the same, and from his own reasoning claims two per cent. advantage for the vertical paddle. To prove his authority for this assumption, he states that it is a well known fact, that with wide throttles the initial steam pressure in the cylinder is from 14 to 2 lbs. less than in the boiler. Now, grant all this, what means has he of knowing what it was in these two steamers? He assumes the mean, (2 lbs.) and yet where is his authority for so doing? In one steamer it might have been 1 and in the other 2 lbs. less than in the boiler, and the extreme difference may as well have existed in these steamers as in any others. Again, his 17 lbs. is composed of pressure and vacuum, the last of which he has also assumed to be the same. Now, it is well known to every practical engineer, that not only do steamers that are similar vary in their vacuum, but vessels of the same dimensions in every respect will often vary a pound: nay, more, when there are two engines in the same vessel, the vacuum is better in one engine than in the other, and they oftener differ than agree. In proof of this, I have the experience of many good engineers, besides my own observation on many steamers. But still further, in all cases that have fallen under my own observation, where a steamer has had two engines unconnected with each other, (except that both obtained their steam from the same boiler,) one of the engines, withVOL. XXI.-THIRD SERIES.-No. 1.-JANUARY, 1851.

5

out any visible cause, would make from a half to one revolution more than the other per minute, being a difference of from 24 to 5 pr ct. If, then, these differences exist where every thing is alike, who shall assume, in the absence of an indicator, that two steamers, unlike in every other particular, shall have the same pressure on the piston. It will at once be seen, that unless all the assumptions of Mr. I. are strictly correct, the two per cent. which he claims may be dissipated at once, and the balance may be against him rather than in his favor.

But, supposing all Mr. I. states to be correct, and that he is fairly entitled to the two per cent. on 20 feet wheels, is it proper to make such a comparison, when he must know that most of our sea steamers have wheels of 30 feet, and our European steamers wheels of 36 feet, and that in both cases the average dip does not exceed one-sixth of the diameter? An engineer who writes in 1850, is supposed to be doing so for the benefit of the present and not the past age. As to his assertions, that the vertical paddle may be made much superior to the radial wheel, by increasing its slip from 19.3 to 25 per cent., I can only say that narrow wheels and increased slip have been often tried, and have not given the results expected; and the mercantile community, both in this country and in England, are still sufficiently stupid to be satisfied with the old wheel, with all its disadvantages. "M." in his reply to Mr. Isherwood, states that in a trial between two vessels exactly alike, except in wheel, the one with the vertical paddle had to make two more revolutions per minute to equal in speed the vessel with radial paddles, and of course the one making the greatest number of revolutions consumed the most fuel. I understand Mr. I. to admit the fact as to the number of revolutions, which he accounts for; but he objects to the remark, that the one making the greatest number of revolutions per minute consumed the most fuel, and states that "M." is the first discoverer of this fact, and he is willing to give him all the credit of it. Now, let us examine into this, and see which is correct. At page 185, September No. of the Journal, we are told by Mr. I. that the power required to work the engine, overcome load of air pump, &c., was equal to a pressure of 2 lbs. per square inch on the piston. Now, assume that both of these vessels had single cylinders of 70 inches diameter, 8 feet stroke, and that the one with radial paddles made 16, and the one with vertical paddles 18 revolutions per minute, the power lost in working the engine will be as follows:

From this data, given us by Mr. I. himself, it is very evident that more power has been expended in one engine than in the other to overcome friction, &c., and an increased expenditure of power involves an increased consumption of fuel, and, on this account, the increased loss from radiation. Clearance at the ends of the cylinder, and at steam ports, caused by oftener filling the cylinder, is not taken into account, and would show a greater difference than I have given.

Mr. I. states that the experiments made at Maudslay & Fields, and

witnessed by Mr. Barlow, were made without any sagacity of method, and both the experiment in its conduct, and the conclusions drawn from it, are erroneous. To prove this, I hope he will give us something more than assertions; a course of practical experiments, witnessed by disinterested engineers, would be valuable, and an assertion has value if supported by fact, but is useless without it. FULTON.

To the Committee on Publications.

Explosion of the Steamboat "Anglo-Norman."

NEW ORLEANS, Dec. 17th, 1850.

GENTLEMEN: Again we have had an explosion of a steam boiler in this vicinity, resulting in a loss of valuable lives and property. I have endeavored to gain as much information as possible from eye-witnesses, and an inspection of the hull and ruins early the next day after the explosion.

As no part of the boiler remains, it prevents certain conclusions being formed of the cause.

The new steam tow-boat "Anglo-Norman," built entirely here, after having been proved by three trips to and from the gulf with tows; the owners and makers invited many of the influential gentlemen of the city on an excursion trip, which took place on the 13th; the boat was run some distance up the river, and on her return, when about eight miles above the city, at 3 P. M., her boiler exploded, killing and wounding many of the persons on board.

For a better understanding I will give some particulars of the boiler. It was of the "wagon form," thirty feet long, sixteen feet wide, and nine and a half high, and weighed about 28 tons; in the interior there were four plain arches, (without any "water bridges,") extending to the back end, and above these were eight return cylindrical flues, about 15 inches in diameter; the water legs or sides were about four inches in the clear; each arch contained a set of grate-bars, and the lower part of the arched flues had the usual brick work and apron; to those practically acquainted with condensing engine boilers, it will be readily understood that this was one of the poorest plans for an economy of any kind of fuel, and more particularly when it was of anthracite coal.

It was made by Armstrong & Co., regular boiler-makers, after a nearly similar one made in New York, and its workmanship appeared good; the only peculiarity I noticed from an outside view was that the iron was lighter than that used at the North for similar boilers; as far as the shell was concerned, and as it was not deteriorated by use, I considered it amply strong for a working pressure of fifty pounds to the square inch. I have understood that it was not intended to exceed the thirty-one inches of the mercury guage, but as the small tube of the guage took the steam from the end of the steam pipe some thirty-five feet from its attachment to the steam drum, it of course was not a correct indicator of the pressure in the boiler when the engine was in motion; not having seen the boiler after it was placed on board, I rely on others;-the safety valve was