OIL FOR WATCHMAKERS-STRENGTH OF LEATHER, &C.

STRENGTH OF LEATHER-FORCE
AND VELOCITY OF HAMMERS.

135

SIR,-Various engagements have prevented me, hitherto, from replying to your inquiry.

the surface of the sugar, which the alcohol detaches with great difficulty, accordingly the moment the molasses begins to run, the surface of the sugarloaf, contained in the form, is to be scraped and a litre of alcohol First, to A B. C., respecting my 36 degrees above proof poured by experiments on Leather, I beg to degrees over the surface, the little observe that the pieces subjected to orifice of the form being stopped and my experiments were short, varying the base of the form being carefully from seven to fourteen inches in covered to prevent evaporation. In length; about two inches at each two hours the orifice at the bottom of end were occupied by the vices made the form is opened and the alcohol use of in the experiment; the extenruns off in the pot charged with sion in all the specimens appeared a great proportion of the colouring most towards the centre of the pieces, matter; the operation may be repeat producing in that part a proportioned with half the quantity of fresh ate contraction in width and thickalcohol, the sugar is equal in white- ness. I think it very probable that ness to powdered sugar. It is then the mode of attaching the vices to melted and put in the boiler with the leather prevented the contracbullocks blood. The operation is ter- tion near the ends, which otherwise minated by claying the sugar. The would have taken place. beet furnishes 3 or 4 per cent of raw sugar, and sometimes from 4 to 5.

OIL FOR WATCHMAKERS.

H. C.

SIR,-Seeing in your excellent Magazine, an inquiry for the best method of procuring the finest Oil for Watchmakes, I have great pleasure in informing you of the most simple and certain method of purifying olive oil, and which I have seen tried with great success by Dr. Nooth, F. R. S.

Put the oil into a white glass bottle, hang it up in a window exposed to the sun; in two or three months it will be as clear and white as water, all the impurities being thrown to the bottom. The bottle in which the experiment was tried was square, and it was remarkable, that the sediment did not settle regularly to the bottom, but seemed thrown into the four

Second-Some of the fractures took place through the whole substance nearly at the same time, whilst others commenced on one side, in consequence of the resultant of the force not perfectly coinciding with the centre of the straps, although care was taken to make this coin

cidence as near as could be, and probably nearer than in the common use of leather straps will be found to be the case. One of the specimens of cow-hide was a little cut by the vice, and began to separate partially.

I am aware that if the straining force be applied to one side of a broad strap, it will be torn with less force than if all the parts of the substance are allowed to act together, just as we tear a sheet of paper by beginning at one edge.

Third-I did not measure the degree of elasticity in the course of my experiments. I am aware that it would be of some importance to determine the elasticity, and had there been any considerable share of this quantity visible, I should have done so; but I soon perceived the proper elasticity to be very small, and that whatever extension was produced by the weights nearly remained after the weights were removed. I also observed that many of the specimens suffered a considerable exten; sion before they became sensibly impaired in strength.

being a diversity of conjectures on
the subject, and a desire to promote
scientific observation, will, I hope,
plead my excuse for troubling you.
I am, Sir,

'The above being the greatest velo- as great as if it were a drum-head. I cities, and as the least velocities may beg to know if any of your intellibe any thing above eight feet per gent readers can explain the reason second, the medium may probably of the above-mentioned action; there be not far from what I have given in my former letter. I find Dr. Young quotes Professor Robison in a note, and mentions twenty-five feet as the velocity of a carpenter's hammer; but the page or article is not referred to; if any of your readers can point out the place, perhaps something 104, High Holborn, more interesting may be found. Nov. 16, 1824.

I am, Sir,

Your obedient servant,
B. BEVAN.

Your obedient servant,

J. W.

Leighton, Dec. 7, 1824.

SINGULAR EFFECT OF PRESSURE.

PREPARATION OF BORAX IN PERSIA. CRELL'S Annalen for 1791, describes this as follows:-The water of an alkaline spring, which is hardly an inch in diameter, is collected in SIR.-I observed a few days back, marble basins, and thence is conveyin the brewhouse of John Nealds, ed into untinned copper kettles, where Esq. at Guildford, that the slightest it is mixed with blood, urine, and pressure of the thumb on the head scrapings of leather, and allowed to of the barrels of aie or beer, whilst putrefy for five or six weeks. The working off the yeast, caused it to deposite at the bottom of the kettle is rush out, more or less, according to then boiled with water, and on coolthe pressure. Now, though the head ing, a rude but not crystallized speof a cask of that description is at least cies of borax, called by the Persians inch and a half oak, yet the effect is bora, is obtained.

( 137 )

CAUSE OF SOME STEAM-ENGINES REQUIRING MORE FUEL, OR USING MORE STEAM, THAN OTHERS, ALTHOUGH DOING THE SAME WORK.

SIR,-A few days ago, I happened where the lines, cccc, intersect the circle, to see two steam engines at work dd, are drawn perpendicular lines, e e e e near each other; the one was the perpendicular lines are also drawn in the crank circle, shown by ff ff. Hence it is improved double reversing steam- evident, that the lines indicated by e have engine, the other a continuous rotato- the same proportion to the oval formed withry steam engine. this last was doing in the cylinder, a a a a, as the lines ffff, which are contained in the crank circle to the most work, yet not consuming the circle bb. The intersection of the lines half the quantity of coal as the re- marked e with the lines 1, 2, 3, 5, 6, and 7, versing engine. This led me to cou- gives the definition of the oval in the cylinsider the cause, which may be un- der, which shows the distinction between derstood by the following description which must be used by the reversing engine the effectual and ineffectual portion of steam of the properties of the reversing en- to give a rotatory motion by means of a gine as it communicates its power to crank. The part of the oblong figure, aaaa, machinery by means of a crank. outside of the oval, shows the quantity of steam used in the reversing engine, more than that which would produce the same effect, in case the power was applied continuously and directly, and not reciprocally.it ineffectual (use of) steam. The parts of I have therefore taken the liberty of terming the cylinder, w w w, show the ineffectual portion of steam used, which is contained the side branches, nozzles, &c. which is unabove and below the piston, together with avoidable. Hence it follows (in round numbers,) that the best reversing (crank-work ing) steam-engines use about nine parts of ineffectual to eleven parts of effectual I am, Sir,

[See the prefixed drawing.]

Description.

a a a a Represents the inside section of a steam engine cylinder, two feet in diameter, and five feet in length, adapted to give a four feet stroke; bb, a circle of four feet in diameter, agreeing with the length of the crank. The perpendicular diameter of this circle is divided into eight equal parts, as shown by 1, 2, 3, 4, 5, 6, 7, 8; through each of these parts lines are drawn at right angles to the perpendicular, until they intersect the circle bb. From each of these intersections lines are drawn to the centre of the circle bb, shown by cc. From the same centre is drawn the circle dd, equal to the diameter of the cylinder, a a a a. Through the places

steam.

Your obedient servant,

A LOVER OF IMPROVEMENTS,

Here, then, the mean difference strength of the rack is but in proporbetween extreme circumference of tion to the cubical contents between wheel and boat is only 2.82 per hour, or the portion lost in driving the water aft. Several other examples might be quoted, and the result would be found nearly the same.

I apprehend, with the present construction of paddle-wheels, this difference cannot be materially lessened without at the same time affecting the velocity of the boat.

The immersion of the floats ought to be calculated so as to absorb the power of the engine at its regular speed.

The position assumed by G. B "That the wheels of a steam vessel ought to be considered as a pinion working into a rack, and that the

the floats"-does not apply: for, were they placed at five and six feet apart, as he suggests, in some diameters of wheels, one float would be entirely out of the water before the next one had entered it, causing great irregularities in the working of the engine, besides loss of power.

I am of opinion, that the best effect is likely to be produced when the wheels have a float for every foot they are in diameter, and the surface brought into action each moment of time should bear a certain proportion to the immersed section of the midship bend. HORATIO.

Tower, Dec. 7, 1824.

CURE OF DRY ROT.

SIR,-Your valuable publication being the medium by which various specifics and causes of the Dry Rot have been stated at different periods, and the subject being one of infinite importance to our naval greatness, I beg leave to offer a few remarks, which I hope will induce your abler Correspondents again to investigate the subject.

Mr. Burridge, in his treatise on Dry Rot, gives winter felling of timber as its only cure. Now, as the adoption of this method would destroy the bark, and thus enhance the price

of oak timber itself, I wish to be in-
formed the reason why American
oak, which is always felled in winter,
is peculiarly susceptible of the dis-
ease when it is used in the construc-
tion of British ships. I consider the
Dry Rot in British oak timber to arise,
more or less, from the nature of the
soil in which it grows; as
we find
that Welsh oak by no means equals
in duration Hampshire growths, al-
though both are apparently good.

The Dry Rot, at the conclusion of the last war, had attained its height in the British navy; the disease was

NEW TALLOW LAMP, &c.

then created and nourished by the pernicious practice of building ships from various descriptions of timber; American, Baltic, and British oak being mixed with pine, elm, and ash, the various juices of which, on being closed up, produce a chemical action, and cause what we denominate dry

rot.

139

ting, one of this description, which I call a Tallow Lamp.

It is constructed of brass, somewhat in the shape of a common candlestick, and is more portable and safe than a candle. When trimmed according to my directions, it will be found equal to four candles, of six to the pound, and will burn with a steady light, without snuffing, &c. for three hours. The degree of light is regulated by turning a small cock or screw with the finger and thumb, when the light is instantly made larger or smaller, and su table to any purpose.

This is evident from each of the above sorts of timber, when used alone in ship building, producing a good and lasting vessel. Look at, for instance, the pine ships of Norway and Sweden, the oak ships of Holland, &c. As a remedy for this evil, I I have used this lamp to solder would recommend the discontinuance with ever since I made it, and find of the practice of using various sorts that large and small articles may be of timber in the same ship; and that soldered with pleasure; spirits may when the vessel is on the stocks, all also be evaporated, eggs cooked, and between the timbers should be filled silver, gold, or brass melted by it. with salt, which effectually prevents One pound of tallow and three inches vermin, and by destroying any living of wick will light up one of my lamps principle in the timber, eradicates for six nights, burning three hours dry rot. The national and mercan- each night. tile navy of the United States of America have long used salt with the greatest advantage, and I have seen several ships so treated open perfectly sound. The first apparent objection to salt is the creation of damp; but an inspection of the American packet ships at Liverpool, or elsewhere, will remove any prejudice on

that head.

NEW TALLOW LAMP.

I am, Sir, &c.

M. MONNOM, Watchmaker. Broadway, Worcestershire.

[We shall be glad to receive a more particular description of the construction of this apparently useful lamp, and a statement, founded on the inventor's experience, of its economy compared with candles.-ED.]

UNION OF COPPER WITH IRON, &C. BY MR. P. N. JOHNSON, MINERALOGIST

AND ASSAYER

The combination of Copper with Iron, although stated by many writers on metallu gy to be capable of uniting in an indirect way, is yet by most operative men, as casters of copper, and others, positively denied to have any such capacity.

I have had my attention directed to this subject, by being summoned as an evidence in a cause Smith vs. SIR,-In perusing your Magazine, Frost. Mr. Smith, who uses copper I find the description of some very pans to boil the ingredients for making curious lamps. Now, it strikes me, a green pigment for painting and dyethat if lamps were constructed to ing, had been recommended to make burn tallow instead of oil, the light use of cast pans, to save the expense would be greater, and the smoke and of wrought ones; but these not ansmell imperceptible, compared with what is produced by oil. I have in my possession, and of my own inven

swering his purpose, he employed me to inspect and give my opinion on them. In my experiments I proved