charged with its saturating equivalent, or about eight ounces of steam, at the temperature of 2129, and with an excess beyond that equal to a pressure of 10 lbs. above that of the atmosphere. Let B represent the space above the water, and indicating a corresponding pressure of 10 lbs. If then, by any means, this excess in A be suddenly liberated and discharged into B, say by a removal of the pressure, as when the engines are set to work, there will necessarily be a great and sudden increase in that space both in quantity and pressure.

Now, there are several circumstances which will suffice to cause this escape of steam from the dense medium of the water into the lighter one above it. Not only the removal of the pressure, but even the introduction of cold water, as from the feed pipe, is found to cause such a sudden grouping of the steam, as shown in the case of ebullition, as will effect its discharge from the water, as shown at page 74, fig. 23.

Let us, then, suppose a boiler with a due supply of water, the thermometers indicating a temperature, both in the water and above it, say at 250°, with a pressure of two atmospheres, or 30 lbs. on each square inch. On the valves being opened and the engine set on, we can well conceive the rapidity and violence with which the steam would escape from the water into the space above it, and the consequences of such a sudden discharge in the event of any part of the boiler being then at its maximum strain.

Under such circumstances no valve could possibly be sufficient for the escape of both the steam and water thus suddenly requiring relief; and from what we see in the small case of the experiment before us, we can appreciate the violence with which the steam would rush from the dense medium of the water when relieved from a pressure of perhaps 100 lbs. to the square inch. In this sudden enlargement and effort to escape, we see, then, abundant sources of danger.

We know that the rapidity with which a balloon rises will be influenced by the density of the air medium at the earth's surface, and the lighter medium in the upper regions of the atmosphere. So must it be when the steam atoms, or, as we may

call them, balloons, by any sudden diminution of the pressure, are enabled to rise from the water into the space above it. Those who may still be incredulous as to existence of steam in the water, let them make the following experiment, and answer the following queries.

Let Fig. 45 represent a bottle, nearly filled with

water up to A. Let the cork be pressed in so as to bear a pressure equal

to a temperature of 220°, Fig. 45.

or thereabouts.

Let the

heat be applied until the cork be forced out, which will be in a few minutes after boiling has commenced. On this quasi explosion taking place the entire mass of water will be seen violently agitated by the sudden liberation of the steam, and its forcing before it a large portion of the water, which will descend like a shower bath. It will then be found that nearly one-half the

A

water will have been forced out by the action of the steam. Let the operator then say what was it that drove the water out, and why the temperature was instantly reduced to 2129 He will be satisfied that nothing but the presence of steam, diffused through the water, could possibly have produced the explosion.

Some experiments were lately made in America by the Franklin Institute, in which explosions in iron and copper vessels were intentionally made. In one case a leak or fracture had existed,

Z

through which the steam escaped with considerable force. It was then conjectured that the fracture had become suddenly enlarged, and which would be tantamount to a sudden opening of the engine valves and discharge of the steam. This idea, although entitled to consideration, leaves us still unenlightened as to the cause of the increased pressure, in the face of a reduced quantity of steam. It will be seen, however, that it bears directly on the subject here referred to, namely, the sudden liberation and consequent expansion of the steam from the water medium, at the moment there was a maximum strain on the boiler.

Dr. Ernst Alban, in his work on the high-pressure steam engine (page 33), observes, in reference to the disproportion between the steam and water space :-"The great quantities of "steam and water tend to produce frightful consequences in case "of explosion; the former by its great pressure and sudden 66 expansion, the latter by its instantaneous conversion into steam "by the removal of the pressure, as all the free caloric beyond "the boiling point is spontaneously applied to the formation of "vapour."

There are here several capital errors. 1st. The assuming a great pressure of steam on the water, whereas the pressure acts upwards equally as it does downwards, a fact which the uniformity of temperature in both places should have pointed out. 2nd. The assuming an instantaneous conversion of the water into steam by the removal of the pressure, which, however, relieves the steam in the water equally and simultaneously with that in the space above it.

Again, there is really no ground for the supposed existence of free caloric-that is, caloric uncombined or unassociated with the water in the state of vapour or steam.

The Doctor concludes his work with the following exhortation : "Prove all things; hold fast that which is good." We might here call on him to adopt his own recommendation, but to begin by proving what he merely assumes to be good.

APPENDIX.

REMARKS ON THE MODE OF EFFECTING THE COMBUSTION OF COAL IN FURNACES.

The following Testimonials, from high chemical authorities, have been selected from a number of others to the same import, and are here given in the order in which they were received and read by the author, in his Course of Lectures, at the Literary and Scientific Institution, Liverpool.

REMARKS BY MR. BRANDE.

Royal Mint, London, 26th November, 1840. MY DEAR SIR,-I am convinced that you are not only practically, but theoretically and scientifically, right in regard to the general views put forth in your Essay on the Combustion of Coal and the Prevention of Smoke. I have long advocated the principles which you have adopted, and have annually illustrated them in my lectures in the Royal Institution; but it

unfortunately so happens that, when scientific men urge new views, or suggest the practical adoption of rational theories, they are neglected, because it is presumed they are merely founded on unsubstantial hypotheses; and, on the other hand, when practical men attempt to found improvement on scientific principles, they are sneered at as dabblers in science; and so, both become disheartened and disgusted, and the only people who are temporarily successful are quacks, who, pretending to what is called originality, and, neither referring to practice or science, steal from both; but, deficient in all knowledge of their own, ultimately mislead their followers, and, like the alchemists of old, not unfrequently deceive themselves.

Under these circumstances, it is really refreshing to find a person of your experience willing and able to blend practice with science and theory; and I have no hesitation in saying, that the views promulgated in your Essay are substantially founded upon just and scientific principles.

When the unburned hydrocarbons, which are produced during what is commonly called the combustion, but which, in reality, is principally the destructive distillation, of coal, in our ordinary steam-boiler furnaces, gradually mix with air, they assume the form of what is called uninflammable smoke; but, if they be examined immediately after they leave the fuel and before they have blended with excess of cold air in the chimney shaft, they are found to be highly inflammable and rich in carbon. At this point it is that you judiciously admit the jets of air; and in so doing, every jet which enters the inflammable atmosphere within the flues becomes, as it were, the centre of combustion, and tends to increase the heat by burning and destroying that hydrocarbon which otherwise would go on to produce worse than useless smoke.

When air is admitted in a body to fuel, it never can effect those useful purposes which are obtained by admitting it in due proportion to the intensely-heated inflammable vapours and gases; or, in other words, to the products of the distillation of coal, at such temperature that they may take fire in its contact. In this way each jet of air which you admit becomes, as it were, the source or centre of a separate flame; and the effect is exactly that of so many jets of inflammable or coal gas ignited in the air: only, in your furnace, you invert this ordinary state of things, and use a jet of air thrown into an atmosphere of inflammable gas; thus making an experiment upon a large and practical, which I have often made on a small and theoretical, scale, in illustration of the inaccuracy of the common terms of "combustible" and "supporter of combustion,” as ordinarily applied.

I fill a bladder with coal-gas, and attach to it a jet, by which I burn