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amine the theoretical conditions and the phenomena | bustion is incomplete; that is when the hydrogen
attending the combustion of the gases in the ordinary
working.

burns before the carbon.

Messrs. Morgan Brooks and J. E. Steward (of Stevens Institute of Technology), recently contributed to Van Nostrand's Engineering Magazine a report on some experiments upon the "Otto" gas engine, describing a careful examination, both theoretically and experimentally, of the performances of that motor, and an investigation in which the distribution of heat is useful, and lost forms of energy was determined.

In the working of the "Otto" engine the forward motion of the piston draws into the cylinder air and an explosive mixture of air-and-gas, the return of the piston compressing this mixture into a space at the end of the cylinder equal to 38 per cent. of the entire cylinder volume. The charge then ignited and the explosion takes place, raising the temperature and pressure to their highest value. The piston is driven forward to the end of its In the experiments there described, a 10 h.p. stroke, and the pressure and temperature fall Otto gas-engine was used, having a stroke of 14in., through work being done on the piston, and the and diameter of piston Stin. Every precaution was heat passing through the sides of the cold cylinder. taken to insure correct results; a 60ft. meter for On the return of the piston a portion of the exploded measuring the gas, and a 300ft. for the air were mixture is driven from the cylinder. The work fixed. The water required for the water jacket done in the explosion and expansion of the gases is was measured by a water meter, and its temperature less than a quarter of the period of two revolutions. both before entering and immediately after leaving Supposing Fig. 5 to be the cylinder and the piston the water jacket were measured by a standard to be at B, and on its outstroke the air and air-and- thermometer. A pyrometer was placed in the exgas are drawn into the cylinder at the port A being haust as near to the engine as possible, giving the admitted by the slide, when the piston reaches the temperature of the exhaust gases. For the purpose port A is closed by the forward movement of the of measuring the useful work of the engine, a slide. On the return of the piston the mixture is brake consisting of two iron hoops with blocks of compressed into the clearance space, E, E, at the Wood fastened at short intervals, was clamped end of the cylinder. The piston is again at the round a 30in. pulley on the crank-shaft of the point B, and the crank is passing the centre; the engine. A strut transmitted the pressure derived return of the slide ignites the mixture at the port A. from the brake directly to a platform scale. By an arrangement of the slide the igniting flame The following is a summary of tests obtained at full is projected into the explosive mixture, and the power:flame spreads, inflaming the whole mass, in time varying according to the quality of the explosive mixture.

In experiments made at the Crystal Palace Exhibition, 1883, with the "Otto" engine, it was found that from the beginning of the rise of pressure to the time of reaching the maximum pressure, the interval was scarcely ever more than I-30th of a second, and was often not more than 1-50th of a second. In cases where the supply of gas was diminished, the maximum pressures obtained were much reduced, and were late in the stroke. In all the experiments with the "Otto" the maximum pressures were higher as the time of reaching the maximum was diminished; this corresponding with the phenomena observed by MM. Berthelot and Vieille with experiments upon incomplete com

bustion.

with only five minutes' interval, more water was used, and the heat given out by the cooling of the previously heated cylinder is added to that derived directly from the hot gases. If the figures 23 horse-power for test 3, and 28 horse-power for test 5, be substituted for those given in the table, they would probably be much closer to the results of a prolonged test.

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Table marked No. 5, and diagram marked B, were the one chosen for the calculations; all results were reduced to horse-power. The "horse-power" in gas "burnt' was calculated from the analysis of Hoboken gas, and is the dynamic equivalent of the heat capacity of the gas; the "horse-1 e-power lost by the exhaust" and by "water-jacket calculated from the specific heats of the discharged gases and of water. The indicated horse-power was computed in the ordinary way from the number of explosions, and the mean effective pressure. An allowance equivalent to a little more than of an atmosphere mean effective pressure was made for the area between the exhaust and admission lines, representing the work done in expelling the burnt gases and in drawing in the fresh charge.

The difference between the indicated and the actual work gives the amount of friction in the engine. The average of the tests at full power is 18.6 per cent. friction, a remarkably good result.

The consumption of gas per horse-power averages 30 cubic feet. The calculations of the gas used show that it was the average of London 16-candle gas, and the results agree with the Crystal Palace Exhibition experiments.

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Horse power
dynamometer)..
Cubic feet of for brake
gas
horse-power per hour.
Length of stroke in inches 12in.
Diameter of piston

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16in. 5.75in. 12in.

The ratio of air to gas, added to the 38 per cent. of the mixture not expelled from the previous charge, was found by actual measurement of both to be about 7 to 1 when the engine was working most economically. When the proportion of air is increased by partly closing the gas valve, the card obtained is like C or D, Fig. 7; the explosion line is much more inclined, the mean effective pressure less, consequently also the indicated horse-power. The gas consumption per indicated horse-power is not much changed, but per effective horse-power it becomes considerably greater, showing the false economy of throttling the gas supply. A comparison of tests 1 and 7, in which the conditions other than the ratio of air to gas are nearly identical, show very plainly the disadvantage of using too little gas.

Fig. 6 is an indicator card taken with a light spring. Beginning at the point 1, the line represents the pressure during the first forward stroke, while gas and air are entering the cylinder. This line lies at a nearly uniform distance below the at

1

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30

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117.5

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806

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Duration in minutes..
Gas, cubic feet
Air, cubic feet
Ratio of air to gas
Amount of water through jacket, c. ft.
Temperature of water, entering
Temperature of water, leaving.
Number of double revolutions
Number of revolutions per minute
Ratio of explosions to double revolutions
Mean effective pressure (atmosphere)
Temperature of exhaust gases in deg. C. 430
Indicated horse-power..
Effective (brake) horse-power
Horse-power lost by exhaust gases.
Horse-power lost by water jacket
Horse-power in gas burnt
Gas per indicated horse power, c. ft...
Gas per effective horse-power, c. ft....

8:0
26.90 25.70 17.6* 20.30
57.60 52.40 52.90 52.30 54:40 56:40
24.50 26.00 24.70 24.60 23.90 24.00 24.80
29.10 30.00 30.00 29.00 30.10 29.50 33.40

The economy in the consumption of gas of the "Otto" engines of small powers is largely due to the incomplete combustion of the explosive mixture, enabling a higher pressure to be obtained at the commencement of the stroke. When the combustion is retarded by the portion of burnt gases left in the cylinder from the previous charge, *In tests 3 and 5 the amounts of heat recorded the maximum pressures obtained are later in the as transferred, in the water-jacket do not fairly stroke, and the mean effective pressure less. represent the heat lost by the hot cylinder gases, Diagrams taken from the "Otto" engine show for the following reason:-In test 3 but little water that the best results per effective stroke are ob- was used, the cylinder thus becoming hotter, and tained when the mixture contains no part of the thus part of the heat was consumed in heating the burnt gases of the previous charge, and the com- metal of the cylinder. In test 5, which followed 3

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the clearance space EE at the back end of the cylinder. This compression is represented by the line 2, 3, 4, 5, which crosses the atmosphere line at 3, and shows a pressure of nearly two atmospheres at 5.

One revolution of the engine is now complete, and the charge is ignited just as the crank is passing the centre. The rapid burning of the gases liberates a large amount of heat, increasing the temperature and pressure. The combustion being rapid until the point 6 is reached. At 7 the exhaust valve opens, allowing the burnt gas to escape. The line 8, 9, 10, 11, shows 'the pressures while these gases are being expelled by the second return stroke of the piston.

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C. P. 0.268

1.37.

C. V. 0-196

(To be continued.)

R. A.

SPEED OF EXPRESS TRAINS.

at various times by correspondents of the fastest
[22937.]—A GOOD many tables have been given

It will be seen that out of a total of 66 runs, no less than one-third are made by local trains between Manchester and Liverpool. In the longer runs the Great Western and Great Northern take the lead. The North Western show some improvement, and are now running a train between Manchester and London in four hours and a quarter. The Midland expresses are handicapped by severe gradients, and mostly average 49 miles per hour.

I agree with "Nun Dor." that the wonderful performances in America, and on the G. W. R. 40 years ago, cannot be accepted on mere hearsay, and I am quite incredulous of such speeds as 80 miles per hour. I have done a good deal of timing lately, especially on the G. N. R., and though trains run for 20 and 30 miles together at 60 miles per hour, I have never known one exceed 65.

With regard to loco. engines for high speeds, Mr. Gobert says that it is impossible to use "singles " except with very light trains; yet the fastest trains in the world-namely, the G. N. and the G. W.trains, and the former stiff gradients. On the Caleare taken by single engines, both having heavy

When the governor prevents the admission of gas to the cyclinder, the cycle is somewhat modified. After compression of the air no explosion can take place, since there is no combustible mixture present. The expansion line then follows closely the previous compression line 11, and the cycle is completed by the expulsion of the air, 12 to 13. Two revolutions are required to complete the cycle when the engine takes gas every charge; and 4, 6, or 8, trains in Great Britain; these have been, however, donian the 8ft. singles seem to be most liked. The and sometimes 10 revolutions may occur before the in most cases incomplete, and in some inaccurate. M. S. and L. singles take trains over the Penine engine returns to its original state. I have worked out a table from this month's Brad-(1,010ft.), and one is said to have drawn 20 coaches The line A, Fig. 7, is a copy of the card during a test when the engine took gas once in five times; shaw of every train running at 50 miles per hour from Manchester to Liverpool in 50min., including and B, when the gas was taken every time. Since readers of the "E.M." The mileage and other and over, the result of which may interest some 5min. stop at Warrington. in test A four charges of air passed through the hints have been taken from Mr. Foxwell's statistics cylinder after every explosion, the products of comexpress trains. bustion were almost completely expelled, leaving the clearance space filled with nearly pure air, at a temperature little above that of the atmosphere. The result is shown by the greater area of diagram A, by a more rapid rate of combustion, and a higher maximum pressure.

It will be noticed by the light spring diagram (Fig. 6) that the pressure between the points 9 and 10, fall below the atmosphere. This is due to the rapid cooling of the hot discharged gases in the exhaust vessel, and pipe outside the engine. The contraction of these gases from this cooling is greater than the piston displacement during the early part of the return stroke, thus causing a partial vacuum within the cylinder. To show that this is the real cause, and that it is not due to any inaccuracy of the indicator, a diagram was taken when the engine was running without using gas every time.

of

Between

GREAT WESTERN.

No.

1

Distance. Time. Speed._ of
Trns.
Paddington-Swindon. 774 87 53.2 3
Paddington-Swindon. 77%
52.6
*Bristol-Taunton
52.6 1
Bristol-Taunton
51-6 3
Bath-Bristol
50.0 1

Between

*Manchester
hill

88

....

....

444
448

51

52

118 14

NORTH WESTERN.

*Edge-hill-Orsdal.
Edge-hill-Orsdal

ton

Total 9

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29

34 53.4 2
33 53.2 1

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After an explosion, the pencil followed the line Willesden-Rugby 8, 9, 10, 1. During the next forward stroke no gas Blisworth-Willesden is taken in, and the line corresponding to 1, 2, is Willesden-Rugby drawn; then follows the compression line similar to Willesden-Bletchley.. 411 49 2, 3, 4, 5. Since there is no explosion this time, the Willesden-Northamppencil returns along the wavy line 11, nearly coincident with the compression line. At 14 the exhaust opens, allowing air to enter from without. The pencil does not return to 2, but moves to 12, nearly on the atmospheric line. Since the gases have not been heated, there can be no contraction to counteract the piston displacement; and on the return stroke the exhaust line 13 rises above the atmospheric; that it keeps above the other exhaust line 9, 10 for the whole length of the stroke, is a still further confirmation of this reasoning.

Between

50-2 2
Total 10
No.

Distance. Time. Speed. of
Trns.
Liverpool-Stockport..37% 45 50.3 2
GREAT NORTHERN.
No.
Distance. Time. Speed. of

Between

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From the tables it appears that the amount of heat carried off by the water-jacket is about half of Hitchin-Huntingdon.. 263 30 the total heat of combustion of the gas burnt. +Hitchin-Peterboro'. 444 When the cylinder is kept cool by a plentiful supply Finsbury-Peterboro'. 78% of water, the quantity of heat carried away appears Grantham-Doncaster. 50 to be greater than when less water is used, and the Huntingdon-Finsbury 564 cylinder allowed to become warmer. From this, Wakefield-Retford 37 one is led to expect a greater percentage of useful Finsbury-Peterboro'. 73% work with less water. But a careful comparison of Peterboro'-Grantham. 29 the results fails to show that any marked difference Grantham King's in either the indicated or the actual work is caused Cross by varying the temperature of the water-jacket. It is probable that much more heat is lost by direct radiation, when the cylinder is warm, then when it is cool, and that this accounts for the apparent difference in the quantity of heat carried away by the water-jacket in the two cases.

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23

The following comparison is not in favour of coupled engines:

G. N. R. train of 13 coaches, drawn by an 8ft. single, after running up nine miles of I in 178, speed reduced to 36 miles per hour.

G. E. R. train of about 10 coaches, drawn by a 7ft. coupled, after running up three miles of lin 150, speed reduced to 30 miles per hour.

Similar comparisons with Midland engines would prove interesting. A very large driving wheel is not necessary for high speeds. A G. N. driver told me that he could get quite as much, if not more, speed out of the old 7ft. singles as the new 8-footers, but that the former could not manage the long runs nearly so well as the latter.

Will Mr. Stretton or "Meteor" say what advantage is gained by having the leading and driving wheels on an engine coupled, as in the Gladstone, L. B. S. C.? Is there not any danger of the engine leaving the rails, when running fast round a curve, with such large leading wheels? June 20.

runs."

Lincoln.

HIGH RAILWAY SPEEDS. [22938.]-I THINK "T. M. R." (p. 346) scarcely understands the position I take on this matter. I do not doubt that both Mr. North and himself believe the statements made to be facts, and quote them in all honesty. What I challenge is the alleged "facts," not the bona fides of your correspondents. "T. M. R." tells me I shall find on p. 7, this volume, some "officially verified What I really find is an extract from the Engineer; but no proof whatever of the statements made. The Engineer, in fact, does not bear out Mr. North's statements; but states definitely that the "fastest journey on record" was made on May 11, 1848, with loco. Gt. Britain, four carriages and a van, which ran to Didcot (53 miles) in 47 minutes, an average of 68 miles an hour. I know very well that if fast speeds can be run anywhere it is on the Great Western line; but I can find no mention of the exceptional rates I have challenged in the Mechanics' Magazine or in the "Life of I. K. Brunel," by his son (Longmans). The speed challenged is 18 miles in 15min. 10sec., which, dropping fractions, may be said to be 72 miles an hour. I want to know how the time was taken. It takes an expert athlete 10 sec. to run 100 yards; but it is a common thing to see the time of the 100 yards race at local and school sports given as 103, 102, 10 secs., when it is clear to those who know that a mistake has been made. I am quite aware that a very high rate of speed can be maintained for a short time-down a bank, for instanceeven with a heavy train; but I am quite sure if the test were properly applied that 80 miles-not to speak of 84 miles-would be non est. By the way, is there any train in the world which actually covers 60 miles in one hour? hope I have made myself understood this time. I have no doubt the runs in question were officially verified in all good faith; but how were they "verified"? It is the Trns. easiest thing in the world to make a mistake of a few seconds, and nothing like these extraordinary runs have ever been discovered when the speeds were accurately taken. Nun. Dor.

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Total 26

No.
Distance. Time. Speed._ of
444 53 50·1 1
MANCHESTER, SHEFFIELD, AND LINCOLN.
No.
Between
Distance. Time. Speed. of
Manchester-Warring-
Trns.
18 53.3 14
Manchester-Liverpool 34 40 51-0 4

ton

16

Total 18

It is somewhat difficult to distinguish between
arrival and departure times; but the following de-
ductions have been made where asterisks occur:-

3min. for down trains at Taunton, 2min. for up
trains at Edge Hill, Imin. for down trains at
Finsbury.

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BAILWAY ACCIDENTS AT CROWDED

STATIONS.

[22940.]-THE suggestion made by "Plain Fact" "that the train should be stopped before it has entered the station and just before it reaches the crowd of eager passengers, and should then remain stationary until it is filled by all who do not object to the want of a platform. Afterwards, the train could fully enter the station for the remainder of the passengers, who would, no doubt, be generally much in the minority," if acted upon, might still lead to accidents, from the difficulty experienced in climbing up the steps of the carriages, which are generally placed a long distance apart.

I would suggest the afore-mentioned passengers should "board the cars 99 a station or two away from the crowded one, as they might like the walk, and it would save the time wasted in making an extra stoppage of the train.

Unvarnished Truth.

RAILWAY SIGNALLING. [22941.]-THERE is a worse case than that at Kentish Town mentioned by "Nun. Dor." (letter 22895, p. 346) at Dalston Junction on the North London Railway. There the down trains to Poplar cross the up-line from Chalk Farm just before they enter the Dalston station after running down a steep incline. The down Poplar and up Chalk Farm trains are timed to meet there every quarter of an hour throughout the day. The Chalk Farm train would foul the other if it ran less than two engine lengths beyond its usual place of stopping, so that if the (chain) brake failed a collision would be almost inevitable. Formerly the signals were interlocked, so that the Poplar train should not cross until a crossing was opened by which the Chalk Farm train would, if it should overrun the platform, cross to the western up line. Of course, it might thus run into another up train; but it would gain the length of the crossing, avoid an almost certain collision, and have also a fairly good chance of entire safety. This is not now the case, and an accident seems very likely.

N. L.

AMERICAN LOCOMOTIVES. [22942.]-"NUN. DOR.," (letter 22773) is in error when he says 66 on page 464, No. 878, there is something of an authoritative description of the locomotive" (meaning that with the Wootten firebox.) The one described is a totally different engine, with a width of firebox of only 43 in., and is a fine specimen of the usual style of American locomotive. The Wootten runs on the Philadelphia end of the line (Philadelphia and Reading Railway) to Bound Brook, from which point the Baldwin engine takes the train over the Central Railroad of New Jersey to Jersey City. On this portion of the line I have timed successive miles in 50 seconds (72 miles per hour). I do not think this is unusual; indeed, it is stated that a speed of 80 miles per hour is sometimes attained. It is necessary, in order to make the schedule time of one hour fifty minutes for 89 miles, that very fast time be made every day on those parts of the line wherever possible, for there are four stops to be made, and considerable distances where fast running is not allowable, as through the streets of Philadelphia, crossing the long bridge and trestles over the Delaware river, crossing Newark Bay, &c. Probably the writer of the letter in the Scientific American referred to is not far wrong in the times given, but he falls into two very confusing errors: Ist, He calls the road the Pennsylvania and Reading, thus confounding it with the rival line the Pennsylvania Railroad; and 2nd, he speaks of Princetown Junction (a station on the latter road) no doubt a lapsus pennæ for Trenton Junction. I do not think you have ever published a description of the Wootten locomotive. I will see if I cannot obtain, and send you one. I think it would be of interest to your readers. By its use the Reading Company is able to use the "culm" or coal-dirt which accumulates in constantly increasing quantities near the mines. In appearance this engine is very peculiar; the boiler sits very high, and the engine-driver's cab, instead of being set at the rear, as in the usual American pattern, is well forward.

Philadelphia, June 6.

E. P.

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of piston stroke, the crank speed being constant, the piston speed must be intermittent.

For instance, with an average piston speed of, say, 800ft. per minute, the piston speed aty, or commencement of stroke, is about 10ft. per minute. At the and (or half stroke) the piston speed is about 30ft. per minute. Consequently, we obtain the following results from the indicator card :

=

661b. x 10ft. p.m. () x 100 sq. in.

33,000

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effect is so like electrical attraction that a deaf man might easily suppose it was the same thing. In this case the air contained in the resonator is charged with sound by the organ-pipe, and causes the attraction by its vibratory motion; the air, however, has too little inertia in proportion to its bulk to maintain the movement more than a fraction of a second; but, in the ordinary lecture experiment with two tuning-forks and resonance boxes in unison, the sound produced by one is conveyed by means of the air to the other, which arrests it, and stores it up so that it continues

2 indicated horse-power for of stroke (at to sound after the tuning fork, by which commencement).

661b. x 30ft. p.m. (%) x 100 sq. in.
33,000

= 6 indicated horse-power for the of stroke (at half stroke).

The consumption of steam being the same in both cases, at the we must deduct something like 50 per cent., thus giving six times the useful effect at the half stroke, when the crank is at its greatest leverage. With the early cut-off engine we obtain the following results from the indicator card :

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1.5 indicated horse-power, for the of stroke (at half stroke). Now, if we deduct 50 per cent. at the o, we do not get a very great indicated horse-power from our early cut-off engines. I have deducted 50 per cent. at, or commencement of stroke, on account of piston force, and crank being in direct line, or on dead centre, consequently not producing any useful effect; the high initial pressure at, or commencement of stroke, being very misleading, the crank being at dead centre and least effective, and least speed and least leverage. When the crank is at, or half stroke, the crank's leverage is greatest, and also piston speed greatest. In the compound engines the steam can be carried to of the stroke, thus giving the greatest amount of pressure when the crank is at its full leverage, or most effective.

In direct acting non-rotative engines, the piston speed is nearly constant, and effect constant.

C. J. Little.

ELECTRICITY A VIBRATION. [22945.]-I AM glad to find Mr. J. Parker Down is willing to oppose my theory on experimental grounds only, and also that he has advanced his objections to the point at issue so concisely in letter 22916, I therefore reply seriatim as requested.

(1) In my letter two opposite electricities, not "two opposite charges" are objected to as a plausible idea, for two opposite charges may be produced by one kind of electricity, which is probably a vibration of matter, and not an inherent quality, as he asserts; matter, however, possesses inherent qualities which enable it to produce the effects of sound and electricity; but why he should state that sound is abnormal I cannot guess, for in many instances electricity seems much more so.

Sound is an expansive force like heat, or electricity, and from a rough experiment I estimated that the expansion produced on the air close to a loud organ pipe was from 05mm. to 15mm. of the barometer column: the amount of expansive force is therefore very small.

(2) You can charge a tuning-fork or other sounding body through the medium of the air which corresponds to electric induction; for example, if the aperture of a moderate sized resonator is presented to a cork ball fixed at the end of a needle which turns on a pivot like that of a compass, on sounding an organ pipe of the proper tone placed near it, the cork ball will be attracted to the mouth of the resonator from a distance of an inch or so. The

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Influence is a production of mechanical effect or sound by motion. For instance, a tuning-fork moved towards the ear becomes sharp, because more vibrations affect the ear in a given time than if the fork was stationary; the extra mechanical effect is in proportion to the extra number of vibrations reaching the ear. Voltaic electricity has been noticed in one of my former letters. There are a great many cases that could be explained more fully, but would take too much time and space.

(4) The argument about electricity being a vibration does not rest on the rupture of gold leaf by sound, and the piercing of a hole in a sheet of paper by electricity, but upon the specific phenomena of the double raised edge produced round the hole in both cases. In the case of sound, this raised edge is occasioned by a force which passes from a greater to a less degree of intensity; in the case of electricity from a higher to a lower potential, and as in both instances the observed effects are similar, therefore I conclude that the causes are also. Sound is as little understood as electricity, and the mechanical phenomena alluded to are not in themselves electricity or sound, but only the effects.

(5) The resistances of the pipe to the flow of water, and the air to a bullet, has nothing of the nature of the resistance of a conductor to the transmission of sound, for a thin iron rod takes a longer time to carry the sound from a tuning-fork than a thick one; therefore a thin conductor has a greater resistance, as in the case of electricity. Force only is transmitted by the conductor, but in the case of the flow of water, or the motion of a bullet, material substances are transmitted from one space to another. J. Sutcliffe.

Photographic Printing in Colours.-Mr. J. Sherlock recently read to the Photographic Section of the St. Helen's Association for the Pursuit of Science, Literature, and Art, the following paper:In this process it is necessary to use coloured negatives-that is, ordinary negatives which have been hand-painted in their proper tints with transparent colours. 1st. Take a piece of ordinary sensitised paper and wash it, to remove any free silver nitrate. 2nd. Place the washed paper in a solution of protochloride of tin, and expose to weak light until the silver chloride is reduced to sub-chloride, and the paper assumes a uniform grey colour. 3rd. Float the paper in a mixed solution of chromate of potash and sulphate of copper, and dry in the dark. The paper is now sensitive to all the colours of the spectrum, and by printing on it with a coloured negative the colours of the negative will be reproduced. After printing, wash with cold water, and dry.

Making Plaster set Quickly or Slowly.-In order to make plaster set quickly, mix it with water into which a little sulphate of potash has been dissolved. To make it set slowly, mix it with fine slaked lime. The time of setting may be regulated by changing the relative quantities.

Indian Ink Running.-If it is for drawing plans you may prevent it running by adding a little sugar to the Indian ink.

REPLIES TO QUERIES.

In their answers, Correspondents are respectfully requested to mention, in each instance, the title and number of the query asked.

152520.]-American Organ. Mr. Floyd has he would not have said what he has on p. 352. If not read the previous replies carefully, otherwise he will refer to p. 306, he will find that I have admitted that a "slight" difference does sometimes exist in soundboards; but the difference is so slight that it is really waste of time to comment upon it. Mr. F.'s statement on p. 352, that I have said "there is no difference in soundboards," is therefore incorrect. Mr. F. also asserts that the depth of windchest is non-essential, as he states "that

[53714.]-Cylinder.-This querist should read up his back numbers, or procure a handbook on the management of an engine. Why does the engine draw a deal of water in the cylinder? See p. 331, and endeavour to find out something, so that you can state your difficulty definitely.-ESSAR.

watch so as to correct an error of 30 seconds per bottle, and the mercury that falls through will be
week, as he finds that, however slightly he moves practically pure. The residue will be oxides of
the regulator, he produces an error of an opposite foreign metals, sugar, and finely-divided mercury.
kind. Although I am told by good watchmakers-NUN. DOR.
that a variation of half a minute a week is a small
error for a pocket timepiece, yet there is no doubt
that by fine setting and a fortunate touch of the
regulator, much nearer rates may occasionally or
temporarily be arrived at. When we consider that
inch balance-wheel by about one twenty-thousandth
the problem is really to alter the swing of a half-
of its rate, we must expect to find it an operation
of extreme delicacy, as we are really attempting to
quicken or retard' each oscillation by about the
sixty-thousandth part of a second in order to correct
an error of half a minute a week, and less than this
for a smaller error. A plan I have adopted for
giving an extremely fine motion to the regulator of
my watch is shown in the accompanying sketch,

B

1

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[53719.]-An 8in. Spark Coil.-A friend has just drawn my attention to this query, which, to speak frankly, was in some danger of being overlooked. If Scottie" will kindly refer to those communications in back numbers of the "E. M.," which are men. tioned in my letter of January 4, 1884, he will find his inquiry about the connection of the compartments fully answered, and other particulars given that may prove serviceable, if he intends making a large coil. He will also find references to the valuable fountains of most of my own information upon the subject of coil-building. The following account of the construction and action of Apps's patent break is extracted (with the drawing) from

B

the finest tone I ever heard came from a chest barely lin. deep." With regard to this remark, I beg to say that the tone would have been slightly improved if the well had been lin. deep instead of lin. deep. I make this assertion from actual experience, and not from mere fancied ideas; and I may now inform Mr. Floyd that the depth of well is of as much importance as many other similar items connected with reed-organ construction. The first idea of this was given to me a short time back, by a gentleman of 20 years' experience in the organ trade, and since then I have practically proved the information to be correct; and I could certainly give some good reasons why a moderately deep well is preferable to a shallow one, if I were requested to do so. The well, in any case, need not exceed a depth of 2in., and should vary from this according to the number of sets of reeds. I am truly surprised that Mr. Floyd so closely adheres to his erroneous opinions respecting differences in American organ soundboards, after it has been plainly pointed out that he is in the wrong. His own previous assertions are quite sufficient to convince any reasonable person that the inferior tone does not result (in his case, at least) from any imperfection of the soundboard. Mr. F., p. 352, wishes me to tell him "the reason the tone is not good?" In reply to this question, I can only come to the conclusion that the organ in question has not been properly constructed in detail, and that the fault does not result from any inferior condition of the soundboard, but may probably result from unskilful voicing, combined with other imperfect items in the construction of the instrument. This is all I can say without necessary to fix the watch in a vice (holding the page 306 of volume II. of "Gordon's Physical examining the organ in question. When I admitted that the reeds were good, I referred to those belonging to the Mason and Hamlin organ, and not to the reeds which Mr. Floyd has purchased, for without seeing the latter, I am unable to judge as to their condition; but those of the M. and H. organ, I am quite sure, are all right, if they have not been interfered with by Mr. F. I certainly should not have written any more on the subject had not Mr. F. requested another reply, for Mr. F. seems to possess a certain amount of bigotry in the matter, as it seems impossible to convince him that his ideas are wrong, and also that his very limited experience in reed-organ construction is not sufficient to enable him to accomplish such results as he always expects to arrive at. Without a personal inspection of the entire organ in question, it is literally impossible to throw any further light on the subject. I bid the subject adieu!-G. FRYER. [63498, 53712, and 53950.]-Measuring Timber.-I am sure it would be most satisfactory to all concerned if you would get some competent authority to pronounce on the various answers to this question. The only two correct ones have been those of "Poor Labourer," (corroborated by "W. A. S.") and of myself in the No. for May 30. I did not notice "Poor Labourer's" solution when I wrote mine, and beg to apologise to him. The correct answer is 82 2 square feet of wood lin. thick. I explained the theory fully before.-B. A. CANTAB.

where A is a small grooved wheel working on a
screw of 50 threads to the inch. B is a traversing
piece, one end of which works in the groove of A,
while the other is bent round and touches the end
of the regulator. A screw, C, fixes the instrument
while in use to the watch by binding on the screw-
head, which holds down the piece carrying the upper
axis of the balance-wheel (I do not know the
technical name). It is clear that with this arrange-
ment a movement of a hundredth of a revolution
of A corresponds to oth of an inch at the point
of action. But it is a serious business to make the
adjustment with sufficient delicacy, and I find it
bow between wooden jaws), and then while viewing
the part with a magnifying glass, giving the gentlest
pressure to the rim of the wheel A. By these
means I am now enabled to keep a watch by Sir
John Bennett (and which has been exposed to
rough travelling and severe climates) in the same
state of correct going as when I bought it more
than 20 years ago. It seems to me that watch-
makers might add an adjusting tangent screw to
the regulator of each good watch at a few shillings
extra cost in the construction.-RICHARD INWARDS.
[53697.]-Tennis Bat.-I believe the gut is
soaked in warm water before stretching in the bat,
and when nearly dry is coated with almond-oil.
The handles would be cleaned up with fine glass-
paper, no doubt mounted on a wheel in the lathe.

-J. T. M.

[53701.]-Gas Launch.-It is only possible to under very high pressure. Storing in gas-bags use a gas-engine for a launch by having the gas would afford a supply for a very short time, for at least 20 cubic ft. are required per horse-power per hour. Besides, so far as I can see, a gas engine is too heavy for a 13ft. boat-that is, if one big enough to drive it along is required.-NUN. DOR.

[53702.]-Shot.-Surely this question depends for an answer on the quantity of powder used. GUNNER.

[53708.]-Gas for Engine.-A mixture of air and hydrocarbon vapour will of course do to work a gas-engine, and the proportions can be readily found when the composition of the vapour is known by referring to some recent letters on the gas-engine. Brayton's petroleum engine may possibly help this of that on p. 612, Vol. XXIV. Very little has been querist, and he will find an illustrated description heard of it during recent years, and I suspect that ordinary coal-gas, or Dowson water-gas, is both cheaper and more convenient than air-gas made by forcing air through petroleum.-ESSAR.

[53677.]-Moulds for Electrotyping from.I regret that I have no personal experience of moulds made of gelatine and bichromate; but the material recommended by Watt, where objects are much undercut, consists of 11b. of gelatine dissolved in three-quarter pint of water, to which half an ounce of beeswax is added, when solution is complete. This mixture should be warm, but not hot, when used. Gore gives the same, but says the best is made of four parts of thin glue and one of treacle. To resist the action of water, two parts of tannic [53710.]—Purifying Mercury.-I think there acid to 100 parts of dry glue may be used, or the is some mistake about purifying mercury by elecmould itself may be immersed for a few seconds in tricity, and I fancy it would be rather expensive. a solution of ninety parts water, ten bichromate of The simple way of doing it on a large scale is to potash, and then exposed to the sun.-NUN. DOR. get a bottle (preferably of iron, but strong glass [53684.]-Loco. Pump.-This query requires a will do) about four times the capacity necessary calculation, and it is not worth while to make that for the mercury. Put the latter into the bottle with a little finely-powdered loaf-sugar, and shake well until we know why the stroke is limited to 3in. for a minute or two; draw the stopper and blow That is very short, and requires a large diameter.-fresh air in by means of a bellows; repeat the shaking and these operations three or four times, then pour the contents into a cone of good writingpaper, with a pinhole in the apex; place over a

ESSAR.

[53689.] Regulating Watch." Nomen" complains that he cannot alter the regulator of his

contact-breaker consists of a piece of iron, sup Treatise on Electricity and Magnetism" :-"The ported near one end of the core by a brass or steel spring, which tends to pull it away from the core, and to force a piece of platinum soldered on to the back of the spring against a platinum pointed stop, the position of which can be regulated by a screw. The primary current passes from the stop to the spring. A second screw regulates the tightness of the spring. This tightening screw works in all ivory collar for insulation, and usually has an ebonite head. When the current passes, the iron core becomes a magnet, and pulling the spring forward, separates the platinum points, and breaks the current. This, at the same time, destroys the magnetism of the core, and the spring flies back and completes the circuit, when the process is repeated, and thus a constant vibration is kept up. When the spring is weak, the current is broken at a time when the core has but small magnetic duced. By tightening the spring, we may arrange strength, and a feeble induction current is pro the apparatus so that the current is not broken till the core has received nearly its maximum of mag. netisation, and so a much stronger current of in duction is generated." "Gordon's Treatise" is published by Messrs. Sampson Low and Co., of London, and the price of the first edition was 368. A

second edition has lately been issued. I cannot think that this work, notwithstanding its value from another standpoint, would much assist "Scottie" in the actual construction of an induc tion coil. Some very fine coils by Apps are pictured and described; but the descriptions are vitiated by what sometimes seems an intentional vagueness and want of detail.-ERNEST BAUGH.

In reply to "T. M. R.." I believe he is correct in
[53764.]-Sanders-Bolitho Brake, G.W.R.-
saying that engines No. 1118 and 975 are fitted
with the vacuum brake instead of the steam. He
is quite right in saying that the steam brake is
seldom used for ordinary stops; in fact most drivers
have a great objection to using it, especially on the
single engines, as it almost invariably skids the
trailing wheel, and unless there is a leaky carriage
or joint in the train, the vacuum is always power.
ful enough, the vacuum being seldom completely
destroyed till the train has stopped. I have foun
that about 24in. or 25in, of mercury is the averag,
vacuum maintained on a narrow-gauge tra
though I have known a stopping train of 12 cour,
keep up 28in. from Paddington to Bristol
regards the leaking off, about which so much
been said lately, it may be theoretically true
all the power is exhausted before the tr

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stopped; but in practice I often find that it is impossible to move a train which has first been stopped by the brake, and has then stood in a station from two to three minutes without first ejecting, and I certainly think that the leak hole is a great advantage. As to the power which this brake exerts, I have seen long broad-gauge expresses consisting of bogie carriages running into Swindon with nearly every wheel either skidding or just on the skid. I have had a good deal of practical ex perience with this brake, and have never yet seen it fail, but have always found it ready, powerful, reliable, and quick in acting.-FIREMAN.

46

For a tin and wire or zinc and wire cage you Wheatstone bridge. The terminals of peg board are
would require a soldering iron and a pair of snips, marked G or L and L or E, &c., with C and Z ter-
and a few other necessary things that will sug-minals. What I want to know is, How, with
gest themselves.-FERRUM.
these instruments, and not much mathematical
knowledge, to ascertain the resistance of a bobbin

not be able to repair the damage very
[53859.]-Bicycle.-I am afraid that you will
You must have a new rim; the old one cannot be
satisfactorily.
straightened. The forks can be repaired by being
brazed. To braze you require a high temperature,
such as from a forge fire. The proper solder for
brazing is spelter, brass filings, or soft brass wire,
using borax for a flux.-FERRUM.

ex

[53897.]-Buttress Screw.-The question was asked in the "Machine Examination Paper" of May, 1883, and also required the student to show the two other forms of screw-viz., triangular and square thread. When a screw has to resist a force acting always in one direction the screw named is used, of which I inclose a sketch. It has one

[53893.]-Current Regulator.-"Volt's " [53764.]-Continuous Brakes.-Your correplanations do not show where his difficulty is. Is spondent T. M. R.," page 354, asks if a vacuum he sure his machine is series wound? I cannot brake with leakage holes plugged would give as think it; or, if so, it is designed for electric lightgood results as the Westinghouse? When Mr. Sanders first introduced the Sanders-Bolitho brake ing and high E.M.F. instead of the work to which on the Great Western and Midland Railways he the work given it; scarcely any with 6in. of surit is put. It ought to give current proportioned to employed a valve, and had no holes in the pistons. face, and increasing as more work is put into the This system did not give good results, and delays vat.' The same solutions are used with battery or were caused by the brake applying itself when not machine, it is all a matter of quantity of current required, in consequence of a small leakage in the related to surface. I have gone fully into this pipes. The two railway companies, therefore, subject in the new edition of my "Electricity." In afterwards, in 1878-9, adopted the plan of drilling my experiments, the limit of deposit was found a hole in each piston, one object of which was to to be 24 ampères per square foot, and the best equalise the force on each side of the piston, and working is about half that rate. If current really thus prevent the application of the brake by a small decrease of pressure. The result has been, passes I do not see how it can be that little deposit as Col. Rich pointed out in his report on the Port-given off at the plate instead of copper? I should is produced unless the solution is too weak. Is gas skewet accident, "that the efficiency of this class advise him to use a galvanometer in circuit, and of brake is materially interfered with by the find out what is really going on, and also ascertain leakage hole in the piston-head." When the the resistance of his machine, which ought to be Westinghouse automatic brake was first intro- small for this work.-SIGMA. duced, the question of preventing its application by leakage was foreseen, and as long ago as 1873, a leakage valve was introduced which completely overcame the difficulty. It consisted of a loaded or weighted valve, which is forced against its seat by a strong current of air (as when the brake is purposely applied), but which, in case of a leakage, simply permits small currents to pass round it, and escape without putting the brakes on when not required. With regard to the latter part of the question, no vacuum brake is or can be as quick in action as the Westinghouse automatic air; this has been proved in practice, and the reason is not difficult to find. In the first place, it should be clearly understood that there is a Westinghouse automatic vacuum brake of the same design as the well-known air brake; but the results given by it are not in any way equal to those obtained by the air brake. The London and South-Western and Lancashire and Yorkshire Companies do use a vacuum brake without leakage holes, and even with a Westinghouse loaded valve for leakage, yet the results are again far inferior to those given by the air system. The question will doubtless be asked by "T. M. R." why is air pressure so much better than vacuum? A vacuum brake can only have a partial vacuum of about 121b., whereas the Westinghouse is worked by high pressure of about 80lb. per square inch. To make the low pressure of 121b. capable of exerting the necessary power, the areas of the cylinders must be made fully six times as large to do the same work as the high pressure of 701b. or 80lb. This increase in size, of course, increases the cubical contents of the apparatus; a far greater quantity of air has to be moved; hence, slow action, with all its defects and dangers, must follow. A train of 16 carriages requires not less than 41,600 cubic inches of air to pass into the vacuum apparatus, which will occupy about 10 seconds; whereas in the air-pressure system it is only necessary for 1,056 cubic inches of air to be discharged at high pressure, which practically takes only 1 second. The value of the Westinghouse brake has always been its instantaneous action; on the other hand, one great fault in the vacuum system is low pressure, and consequently slow action, which, in case of emergency, is a fatal defect.-CLEMENT E. STRETTON, Č.E., Saxe-Coburgstreet, Leicester, June 21.

[53806.]-Wetting Postage Stamps.-Have circular or letters ready at your left hand on table. Divide sheets of stamps into strips of 6 to 12 in length. Have a saucer or other shallow vessel with right hand, draw its back over the water without water in it at hand. Take a strip by its end in your wetting the front (this is easily done with practice) lay last stamp of strip on corner of letter-put left forefinger on top of it, the finger-nail on the perforation. Press on it, and pull with right hand, and the strip tears at perforation, leaving stamp fixed on letter. Push letter aside and repeat. If you have a "youngster" who can divide, wet, and hand you the strips of stamps, you will get through the work like wild-fire.-A. E. J.

surface normal to the axis of the screw, like the
square thread, and is as cheaply cut as the tri-
angular one. The breech screw of large guns is
made of this form. I think the figure will explain
what H. Hall wants. The inclination of the thread
shown on figure. Also see
is an angle of 45°, and the depth 0.64 of pitch, as
E. M.", page 297,
Vol. XXXVII.-THOS. H. HALL, 85, Lorrimore-
road, S.E.

[53898.]-Soapmaking. I should be greatly
obliged to "London Stone" if he will allow me to
communicate with him upon the subject of soap-
making. My address will be found in the sixpenny
sale column.-F. H.

I

[53898.]-Soapmaking.-Soda crystals has a
hardening effect when added in the frames; but
did not expect a like result when used in the pan,
as it would be likely to be discharged with the weak
lye in settling. Will "London Stone" be so good
as to explain this and the exact time to use it is it
at the fitting?-A LEARNER.

class D; Rosebery, 1877, class D; Abergavenny,
[53921.]-L. B. & S. C. R.-Hartfield, 1876,
1877, class C; Sutherland, 1880, class C; Imber-
horne, 1880, class C; Cornwall, 1879, class D 3;
stone should be Bishopsgate. No 49, class known
Lyons, 1876; Burgundy, class C, goods. Bishop-
as Terriers. Sorry I cannot give dates of last two
or class of 301.-RICHMOND, Portsmouth.

or wire.-APPRENTICE.

lows:-Obtain two or three manganese cells, a [53931.]-Fireman's Alarm.-Proceed as folsmall piece of apparatus called "a relay"? (obtain a sensitive one), and a 4in. or 6in. electric bell-or before you buy a new bell you had better try your old one. Take away the bell from where it is at present, or, better perhaps, disconnect the two wires which are led up to it; underneath the bell fix the relay, which will be inclosed in a small case, on which are fixed four terminals. To the two terminals which are connected with the ends of the

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wire on the reels connect the two wires (line) which you just now disconnected from the bell. Then fix your battery somewhere in the house, carry one pole of it to one screw on bell, the other pole connect with one of the remaining two terminals on relay case, the other remaining terminal connect with remaining screw on bell; and I believe by doing so you will greatly improve matters. You can put a larger bell, if the one you have is not large enough. -B. D. WILLIAMS.

glutinous fluid will fix if sprayed on drawing with [53936.]-Fixing Crayon Drawings.-Any an atmospheric odorator. A mixture to be highly commended, as it resists moisture, dries at once, and preserves the character of the material used in drawing, is as much white shellac as will dissolve in clear methylated spirits.—ARCHIBALD.

[53936.]-Fixing Crayon Drawings.- A simpler and less expensive way than suggested in the replies of the 20th inst. is as follows:-Fill a dish or tea-tray large enough for the drawing with milk diluted with a little warm water, place the drawing in this, taking care that the whole is covered, and leave for a few minutes, then dry. Or the milk may be poured over the sketch from a cup instead of using the tray.-VITA.

[53948.]-Canaries.-If you want to kill your bird, by all means follow the advice of "H. J. S.," and especially that of "Assoc.M.Inst.C.E.," and your wish will be gratified. There cannot be any worse treatment than " powdering" him with some nasty "insect powder," and I am surprised at anyone advocating its use. It will, of course, destroy the insects-and your bird also-the powder [53921.]-L. B. and S. C. R.-In answer to F. being poisonous to him as to them, besides getting W: Brewer, I send the following particulars of into his skin and causing increased irritation. The Brighton engines-Hartfield, D class, built in idea of strewing poison in the sand which your 1876; Roseberry, D class, built in 1877; Aber- bird eats! "Water Trumpeter's" method of getting gavenny, F class, built in 1877; Burgundy, E rid of the lice is a good one; but I think the folclass, built in 1877; Lyons, D' class, built in 1877 lowing better from experience. Every night at Imberhorne, G class, built in 1880; Sutherland, G dusk cover your cage over with a white cloth; class, built in 1880; Cornwall, D3 class, built in during the night the insects crawl off the bird to 1875. Bishopstowe is an old passenger engine the cloth, and if this be removed at daybreak, a belonging to no particular class, stationed at New-quantity of the mites will be found running about, and may be killed by putting the cloth in boiling water, or as they get fewer in number with the finger nail. By repeating this you will soon be rid of your pests without any danger to your bird. I have tried this method for years, and by these means keep my aviary cage quite free from para

haven.-SCOTIA.

[53845.]-Birdcages.-Would not a pair of round-nose pliers do for making the loops? I do not think the wire will require much straightening if taken off a new coil; but short pieces can be straightened by rolling them between two pieces of board. The only tools required for making a [53923.] Electrical wood and wire cage would be a pair of round- "SIGMA."-I am much obliged for replies from nose and a pair of flat-nosed cutting pliers, a "Sigma" and Vincent" to my query, and regret A small hammer, small plane, small tenon saw, a that my information was insufficient. I have a set chisel, and a fine bradawl the size of the wire. of resistance coils and a galvanometer, but not

Resistances.

To

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