IV.-LOCO-MOTIVE ENGINES.

In my investigations respecting loco-motive engines, I shall confine myself wholly to those which effect their progressive motion by means of the adhesion of their wheels upon the rails; the only engines of that kind at present in use which do not, are those of Mr. BLENKINSOPS, at Leeds, with the rack-rail; and as I have not had any opportunity of ascertaining their performance by the test of experiment; I shall not, therefore, attempt to give any opinion of their utility, compared with the other, founded only on report or on bare supposition.

I have before explained the nature of the action of the engine-wheels upon the rails; and the principle by which the loco-motion is effected; the great importance of knowing the precise amount of that adhesion, whereby we may be able to calculate, with certainty, upon what inclination of road, and with what number of carriages, the engines can effect their progressive motion, will be very evident, as, upon that, the whole system of their action is regulated.

This may either be ascertained by continued observation of their performance upon

certain lines of roads; or, it may be made the subject of direct experiment. The great variation in the amount, arising from the surface of the rail presenting more or less adhesion to the wheels, in different states of the weather, renders it difficult to subject the engines to experiments at all the various changes; and almost compels us to have recourse to the two extremes in order to obtain a mean result. I shall, therefore, give the particulars of two experiments, one in the most favorable, and the other in the most unfavorable state of the rails.

When the surface of the rails and wheels are either quite dry or completely wet, the adhesion is the greatest, the surface being then most free from the presence of all extraneous matter; when the rails, on the contrary, are moistened with wet, and partly covered with mud, the adhesion is the least: the mud interposing between the surface of the wheel and rail, diminishes the adhesion very considerably, in the same manner as oil or grease applied to the bearings of shafts, or other rubbing surfaces, reduces the friction. In all the intermediate states of the rail the adhesion varies, and in greater or less proportion, according as that state approaches more or less toward either of these changes.

It will be evident, that the total amount of adhesion is that force which would be required to cause the engine to slide along by its wheels upon the rail, if the wheels were prevented from turning round; or that amount of force compared with its weight, which the friction of other rubbing surfaces bear to their weight. Knowing, then, the friction of iron sliding on iron, and the weight of the engine, we could deduce the amount of adhesion of an engine, compared with its weight; or, by fastening the engine-wheels, and employing a force to drag the engine, loaded with different weights along the Rail-road, we could, by this mode, ascertain the amount of adhesion proportionate to the weight; either of these, though very correct modes of ascertaining the total amount of adhesion, compared with the weight, would not, perhaps, be so accurate a standard for practical application. The force of the steam, at different periods of the stroke, being very irregular upon each wheel, might occasion the result, in practice, to vary from that deduced by the foregoing methods.

EXPERIMENT XXVII.

Loco-motive engine, weighing 6 tons, and containing I ton of water, = 71⁄2 tons, dragged 12 loaded carriages, each weighing 9408 lbs.,

up a plane ascending 134 inches in 1164 feet, and also the convoy-carriage, weighing 12 tons, the wheels not slipping. Rails quite dry. Edge-rail 24 inches broad at the top.

Then, weight of the engine 16800

12 carriages 9408 × 12112896

tal resistance overcome by the engine, (exclusive of the power required to propel itself forward); and, consequently, the adhesion of the wheels upon the rails, when the surface of the rails are dry.

EXPERIMENT XXVIII.

Same engine, with 29 empty carriages, each weighing 3472 lbs., up an ascent of 1 in 324; rails slightly covered with mud, and in the worst state; wheels slipped a little, but the engine proceeded at the rate of about 4 miles an hour.

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Then, as before, 16800 +3360+3472 x 29 96128 × 324= 296 lbs. the gravity of the engine and carriages. Friction of carriages 29 × 16464+17=481 lbs.; which, added to the gravity, gives 481+296-787 lbs., the adhesion in the worst weather.

This latter should, of course, be taken as that resistance with which the engine should

be loaded; and this would be sufficient to drag about 70 tons upon a level road. The engine-wheels, however, as stated in the experiment, slipped a little, and though the progressive motion was notwithstanding kept up, yet such a slipping of the wheels would have a very injurious effect, not only upon the wheels, but also to the rails. The load should not, therefore, be so great as to produce such an effect.

From several years' observation of their performance upon the Killingworth Rail-road, I am inclined to think the above rather too high, without incurring the risk of slipping. There, they travel sometimes with 9 and sometimes with 12 carriages, amounting to 36 and 48 tons respectively. The greatest ascent, upon any part of the Rail-road with the load, is 1 in 330; and in returning, with the empty carriages, 1 in 80. The wheels, in in very weather, slip sometimes with 12 carriages; but the engines, in the worst weather, are never prevented travelling with 9 carriages.

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Taking the latter as the datum, we have 8764 lbs. the

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weight of each carriage × 9 × 330 61 lbs., the gravity

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of the carriages. And 16800 +3360 × 330 = 239 lbs., the gravity of the engine and convoy. Then 9 x 40 – 360 lbs., the friction of the carriages, and 17 lbs. the friction of the

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