is no current; but under such circumstances, I have never seen it explode. I may perhaps mention in what way I became convinced of the insecurity of it. Mr. Roberts has been

employed by me for some years as a manufacturer, &c. of lamps; and on several occasions he told me that he was certain the Davy-lamp was not "a safety-lamp." Although I was aware that Roberts had particularly directed his attention to this subject, and from having been a working miner for many years must have been practically well acquainted with the lamp, yet as he was not accustomed to the niceties requisite in conducting chemical experiments; as I and many others had tried the lamp, and as far as I then knew, it had always been found a security against the passage of flame, I confess I thought Roberts was labouring under an error. At his urgent and repeated request, I ultimately consented to attend at Upton and Roberts's manufactory, to see him prove, if he could, the insecurity of the lamp, though fully persuaded that I should be able to find out some fallacy in his experiments. In a few minutes he showed me that flame might be made to pass through a Davylamp; but thinking that the lamp he employed might not be perfect, I sent for one which I had repeatedly tried, and which I knew to be a perfect instrument. The flame passed through this also. Subsequently I tried the Davy-lamps of some friends, and in every case they allowed the passage of the flame. I then undertook a series of experiments, the result of which is a firm conviction of the insecurity of the Davy-lamp when in motion, or when placed in a current of explosive gas. I think we may easily comprehend why the flame does not pass when both the gas and the lamp are at rest: it depends on two circumstances, namely, the less heat developed in consequence of less gas burning; and secondly, the carbonic acid formed not being got rid of, checks the passage of the flame through the wire gauze. I think, however, that the latter is the most efficient cause, since the gauze will allow the passage of the flame when it (that is the gauze) is not hot enough to be luminous, so that a great heat is not essential. Now when a Davy-lamp is plunged into a jar of explosive mixture, a quantity of carbonic acid is immediately formed, and this mixing with the unconsumed portion of the explosive mixture, diminishes its combustibility, and therefore its explosive powers. If, on the contrary, you expose the lamp to a current of an explosive mixture, the carbonic acid which is developed is immediately got rid of, (as well as the nitrogen of the portion of atmospheric air employed in carrying on the combustion,) and then the flame passes. A gentle motion of the lamp, combined with the current of VOL. XXIV.

the gas, very much promotes the passage of the flame. If, for example, a lamp be held before a jet of gas until it becomes hot (a. red heat is not essential), and then gently moved, the flame will pass, and the experiment may be repeated successively a number of times in the minute. Sir Humphrey Davy was well acquainted with this fact, that carbonic acid diminishes the explosive property of gaseous mixtures. At p. 10 of his work, he says:-" On mixing one part of carbonic acid or fixed air with seven parts of an explosive mixture of fire-damp, or one part of azote with six parts, their powers of exploding were destroyed." At p. 32 of his book, Sir Ilumphrey Davy states that "the consideration of these various facts led me to adopt a form of lamp in which the flame, by being supplied with only a limited quantity of air, should produce such a quantity of azote and carbonic acid as to prevent the explosion of the fire-damp, and which, by the nature of its apertures for giving admittance and exit to the air, should be rendered incapable of communicating any explosion to the external air." It is evident, therefore, he endeavoured to form a lamp which should be safe from the combined influence of the carbonic acid gas, of the azote or nitrogen gas, and of the wire-gauze.

State to the Committee in what way you think the lamp of Messrs. Upton and Roberts is an improvement on that of Sir Humphrey Davy? There are several points of view under which we may regard it as an improvement. In the first place, it is quite evident that the wire-gauze of the common Davylamp partially obstructs or impedes the passage of flame through it; and, therefore, if you employ two layers of wire-gauze, the obstruction is greater than that produced by

one.

Now in practice two layers of gauze are objectionable; first, because such lamps would give very little light; and secondly, because the gauze soon becomes clogged up. But even if these objections could be overcome, there exists a still more weighty one, namely, that the lamp, even with a double layer of wire-gauze, is not secure. I have repeatedly passed flame through lamps of this kind; the experiment occupies a little longer time, because the flame passes less readily through two than through one; but it does pass, and therefore such a lamp is insecure. Now in Upton and Roberts's lamp only one layer of wire-gauze is employed, and therefore there is little impediment to the light. To prevent the effects of lateral currents, they use a cylinder of glass placed external to the gauze. This is one improvement over the common Davy-lamp: it must be admitted, however, that Davy, at p. 136 of his work, proposed screens to increase the security of his lamp; but neither the screens of Davy,

nor the cylinder of glass employed by Upton and Roberts, would of itself be sufficient to make the lamp secure. Hence, therefore, we come to the next part of the improvement made by Upton and Roberts, and which consists in the manner they admit the external air, or the explosive mixture, to the interior of the lamp. Around the lower part of the lamp is a number of apertures, through which the air passes into a chamber, the ceiling of which consists of layers of wiregauze. To increase the security of the lamp, any number of these layers may be employed; they are easily taken out and cleaned, and they offer no impedient to the light: whereas in Davy's lamp, any increase in the number of wire-gauzes diminishes the light. This then constitutes a most important improvement. I now pass on to another improvement in this lamp, and which in fact constitutes its superiority to all other safety-lamps that I have seen when the air or gas has passed through the wire-gauzes, it does not pass immediately into the body of the lamp, but into a second chamber, bounded above by a conical piece of brass, having a central aperture about the size of a sixpence, in the middle of which is the wick; so that all the air passing into the lamp, is brought in contact with the wick, and thus increases the quantity of light evolved; and as the aperture is much smaller than the cavity of the wire-gauze cylinder, the latter cannot fill with flame when introduced into an explosive mixture, so that the flame can never touch the wire-gauze cylinder; and, indeed, between the flame and the cylinder there is no oxygen to support combustion, as may be shown by its extinguishing a taper, we have, therefore, the very condition Sir Humphrey Davy wanted, since no taper will burn in the space between the flame and the wire-gauze; so that you observe we have three impediments to the lateral passage of the flame, a layer of carbonic acid, a wire-gauze cylinder, and a cylinder of glass. The safety of the bottom consists in any number of wire-gauzes the maker may choose to employ, and therefore if the lamp is not safe it is his fault.

Then how is the top of the lamp secured? It is made safe by layers of wire-gauze, and also by having a contracted aperture to the glass, by which the draught is increased, and all the carbonic acid gas that is formed below, by the combustion of the fire-damp, or of the oil of the lamp, as well as the nitrogen of the atmospheric air, contribute to prevent the combustion of a body in this situation, for if you put a lighted taper here, it is extinguished immediately. Thus then this lamp is made safe at the sides, at the bottom, and at the top, by different methods. If the glass should break, the lamp is then a common Davylamp.

Have you made experiments on that lamp in the explosive mixture?—I have submitted this lamp to every experiment I have submitted the Davy-lamp to, and I could never get this to explode; indeed, I have submitted this lamp to a test (oxy-hydrogen gas) which it is not likely to be put into actual practice.

This lamp then is safe in a draught or current of explosion gas?—Yes, it is perfectly safe in any current carburetted hydrogen gas, or of this gas and oxygen, or of this gas and air. I have repeatedly tried it, and the flame will not pass. When the explosive mixture was blown in gently, the flame increased in size; if passed in with violence, the flame was extinguished, but no passage of it will take place through the gauze.

Have you made any experiments in coal mines with it?-No, I have never been in a coal mine with it. My experiments were made with coal gas and with hydrogen gas.

Experiments made before the Committee at the London University, 30th July, 1835, with the Lamps enumerated below:

No. 1, the common Davy lamp; No. 2, ditto, with different seams; No. 3, Dr. Clanny's new lamp; No. 4, Stephenson's lamp, with glass; No. 5, ditto, improved construction of lamp, with glass (Mr. Ayres', Newcastle, lamp); No. 6, Robson's Bolton lamp; No. 7, Refrigerating lamp; No. 8, Dillon's lamp, with a shield of tale surrounding it; No. 9, Upton and Roberts's lamp.

Jonathan Pereira, Esq., further examined :

On your former examination, you were so good as to state to the Committee appointed to conduct the inquiry your views as to the relative safety and value of Sir Humphrey Davy's invention; have you a lamp on that principle before you ?-I have.

Will you proceed to illustrate the views you then advanced upon that lamp ?—There are three lamps present, which are made on Sir H. Davy's principle; one belonging to me, the second belonging to the Mechanics' Institution, and the third one was brought by the Chairman of your Honourable Committee. I propose, in the first place, to show the experiments mentioned by Sir Humphrey Davy, as demonstrating the security of his lamp, and then to prove, that, although a lamp may stand these tests, it may, notwithstanding, be insecure. At pages fourteen and fifteen of his book on Flame, he says, "That, in plunging a light surrounded by a cylinder of fine wire-gauze into an explosive mixture, I saw the whole cylinder become quietly and gradually filled with flame, the upper part of it soon appeared red hot; yet no explosion was produced." We will, therefore, take a cylinder, containing an explosive mixture of atmospheric air and coal gas.

If it be objected that coal gas is not identical with the fire-damp of coal mines, I beg to refer the Committee to the statement of Sir Humphrey Davy, at page 15. "Though," says he, "all the specimens of fire-damp which I had examined consisted of carburetted hydrogen, mixed with different small proportions of carbonic acid and common air, yet some phenomena that I observed in the combustion of a blower induced me to believe that small quantities of olefiant gas may be sometimes evolved in coal mines with the carburetted hydrogen. I, therefore, resolved to make all lamps safe to the test of the gas produced by the distillation of coal, which, when it has not been exposed to water, always contains olefiant gas." I presume, therefore, I am warranted in using an explosive mixture of coal gas and air. [The lamp was then immersed in this mixture.] will please to observe the flame does not pass through the gauze in this experiment; and, therefore, the lamp has stood this test.

You

What is the estimated proportion of gas in that mixture?-About one-seventh part of coal gas. The second method, mentioned at page sixteen of Davy's work, is to place a lamp in a glass receiver, through which is made to pass a current of explosive mixture of coal gas and air. [The experiment was tried.] The lamp stands this test also; the gas burns inside the wire-gauze cylinder, but the flame does not extend through it.

From that do you not show that the gas becomes inflamed within the gauze, but no flame passes into the surrounding atmosphere?—Yes.

Do you apprehend that is the experiment by which Sir H. Davy meant to prove, that, in practical use in mines, a moderate current of foul air falling on the gauze would not produce explosion?-Yes; but there is a third method which he adopted to prove the security of the lamp. At pages 137 and 138, he says, he held the lamp in a blower in a mine belonging to J. G. Lambton, Esq., and he states that the result was, the lamp did not fire the gas till the gauze reached a welding heat, when the iron wire began to burn with sparks, and the explosion then passed. As we have not a mine-blower to use, I shall employ, by way of illustration, a jet of coal

gas.

Will you state the chemical distinction between the gas you are now about to use, and that which you understand is found in the mines of Great Britain ?-The gas found in the mines of Great Britain is said to be light carburetted hydrogen, which is composed of six parts, by weight, of carbon, and two parts, by weight, of hydrogen. Coal gas consists principally of this, but contains also other compounds of carbon and

hydrogen, the nature of which varies with the temperature to which the coal is exposed, the nature of the coal, &c. In other words, coal gas is a variable mixture of different compounds of carbon and hydrogen; the principal one being the gas found in coal mines.

Do you think the gas that lights our streets is a sufficiently near approximation to prove the experiment you are about to make?—I do; I found my opinion on the statement and practice of Davy. It is evident that he considers coal gas a more delicate test for a lamp than fire-damp; but, as I have already mentioned, he thought it necessary to employ coal gas.

Will not the experiment be a test of mechanical, as well as of chemical, agency?— Certainly.

Will your experiments illustrate your theory so far as regards mechanical agency? -Certainly. I now hold in my hand Sir H. Davy's lamp. In order to show its insecurity, I purpose subjecting it to the influence of a jet of coal gas until the gauze becomes properly heated for the success of the experiment. It is evident at the present time that the flame does not pass through the wire-gauze [here the experiment was tried], because, as I believe, the gauze is not sufficiently hot. In the experiment made by Sir H. Davy, which I have already alluded to, I strongly suspect if he had assisted the passage of the flame by a slight motion to and fro of the lamp, the flame would have passed long before the gauze was heated to whiteness. Mr. Pereira having held a lamp for a short time in a jet of coal gas, tried to pass the flame through the gauze by a quick lateral motion of the lamp, but the flame did not pass.] I attribute the failure of this experiment to the weak supply of gas, owing to the slight pressure at the gas-works. I am, however, prepared against this cause of failure, for I have a quantity of coal gas in a gasometer, to which we can apply a strong pressure, but I would prefer firing it from the common gas pipe; and, therefore, I will try the experiment again. [The experiment was tried, but the flame did not pass.]

No explosion has passed in the last experiment?-No.

Do you attribute this to the gauze not being sufficiently heated?-Yes. I find it requires some time to heat the gauze. [The experiment was tried.] The flame has now, you observe, passed, but the gauze is not injured. Now that the gauze has become sufficiently heated, the flame will be allowed o pass readily. The experiment succeeds better at night, when there is a better supply of coal gas.

Do you observe by your eye whether there

is an appearance of redness on the gauze ?I cannot observe any appearance of redness; but I do not think the eye would be a good judge under these circumstances, for the gauze might be heated to a dull redness, without being visible, owing to the strong white light of the gas within the cylinder.

Do you not apprehend it to be very im portant to the miner to know what state the gas is in? Of course it is; and he would observe, by the enlargement of the flame, there was danger. [The experiment was again tried.] You will please to observe that the flame has passed a second time through the wire-gauze cylinder of the Davy-lamp. Let us now try the experiment with a second Davy-lamp. [The experiment was tried, and the flame passed.]

But, in case the lamp was placed in a foul mine, and of course surrounded by an explosive atmosphere, would not the gauze heat much more rapidly than under the circumstances of the experiment you are now performing?-Yes; and I therefore propose presently to submit this lamp to the action of a current of explosive gas. [Mr. Pereira again attempted to pass the flame through the wire-gauze, by holding the second Davy-lump in a jet of coal gas, but the flame did not pass; in a third experiment it did pass.] The experiment, you will observe, will not invariably succeed; and a man, therefore, may try a lamp two or three times, and fancy that it is safe, although it may not be really so; for a lamp that will allow the explosion to pass once only in fifty trials is insecure. Having now shown on two Davy-lamps that the flame will pass when we subject a lamp to a stream of coal gas, assisted by mechanical agency, I propose to subject the Davylamps to another test-namely, to hold them before a jet of explosive gas, composed of coal gas and air. The apparatus before me will enable me to ignite a stream of this mixed gas without the danger of its explosion in the reservoir bladder. The proportions which we will, in the first place, try are, three measures of air to one of coal gas. The bladder containing this mixture I attach to the safety apparatus: I shall call it, by way of distinction, the reservoir bladder. I press on the bladder, and a stream of gas is forced out through this jet pipe. I now apply a lighted taper to the issuing gas, and you will observe a bluish flame is produced; the mixture of air with the coal gas very much diminishing the light evolved by the latter in combustion. I proposc, then, to submit the Davy-lamp to a stream of this gas; and, when I observe the wire-gauze on the opposite side of the cylinder becomes red hot, I have only to project a little coal gas on it, and the flame immediately passes.

[The experiment was tried, and the flame passed.]

The Committee observe that the gauze becomes red hot?-Yes.

Will you try the experiment, by forcing the coal gas against the gauze in the Jed hot state, after having removed the The ? lamp from the jet of mixed gas radiating power of the gauze is so great, that the cylinder cools below redness immediately upon removing the lamp from the influence of the jet of mixed gas. However, I will try the experiment. [Mr. Pereira held the lamp before a jet of mixed gas, until the wire-gauze became red hot, and then quickly removed it to a jet of coal gas about half a yard distant; the coal gas immediately ignited.] You will observe that the flame has passed.

You have succeeded in lighting the gas at the heated gauze ?—Yes; I presume these experiments will be sufficient to prove the insecurity of the Davy-lamp.

Do you not make any allowance for the very rare cases in which the lamp can be tested in practice in the way you have now tested it; I mean in moving it forcibly through the atmosphere, dispersing the whole of the carbonic acid gas, and bringing it back to the jet, with an explosive mixture filling the gauze ?-I apprehend the question to be, how far my experiment is analogous to the circumstances met with in coal mines. In coal mines the miner's lamp is sometimes exposed to immense quantities of gas, and to powerful blowers. I presume, therefore, if I can cause the flame to pass through the wire-gauze cylinder by means of a small jet of gas like this, that the passage of the flame will take place more readily in coal mines. If the miner move his lamp, the danger is increased. A current or motion of the gas by a fall of water may endanger the lamp.

Can you explode the Davy-lamp by a mixture of carburetted hydrogen and atmospheric air, by merely plunging a lamp suddenly from the common atmosphere into such mixture? I have never been able to do it; but the quantity of mixed gas which I have experimented with is so small, compared with that found in mines, that 1 can readily believe explosions may occur in mines which we cannot produce on the small scale. I have frequently tried the experiment, but never produced the passage of the flame; owing in part, as I conceive, to the presence of the carbonic acid, which is produced by the combustion of the gas within the cylinder. However, there is a gentleman in this room who asserts that he can pass the flame under these circumstances. If you please, therefore, we will try the experiment. We

have here an explosive mixture of six parts atmospheric air, and one part coal gas; and I propose, therefore, to fill this large cylindrical vessel with it, and then plunge the lamp in. [The experiment was tried.]

The flame has not passed?-No.

Do you apprehend if that lamp had been moved quickly through an atmosphere, combining the proportions you have just exhibited, that any explosion would have taken place? I think it possible that the flame might pass through the gauze, if the lamp were suddenly introduced into a large accumulation of explosive gas, such as is sometimes met with in coal-mines, though the flame will not pass when the lamp is placed in the very small portions of gas which we can subject it to.

Are you not aware that the proportions of air and inflammable gas in mines vary materially, according to the analyses of different individuals?-The following are the results of some analyses of fire-damp made by different chemists:-

Have you heard of any instance where there was no ignition?-I have heard from Mr. Roberts, that fire-damp has sometimes rushed out (from a sudden fall of coal) with such force that it has blown down doors.

Do you consider that the Davy-lamps you have tried are perfect?-Yes. One of the lamps brought by the Chairman of your Honourable Committee is a new lamp. The wire-gauze of which the cylinders are made appears to me, by comparison with some standard gauzes before me, to have at least 900 apertures to the square; and Mr. Roberts, a lamp-maker, tells me, that this Davylamp which I have exploded has 1,024 apertures. At pages 44 and 45 of his work on Flame, Sir H. Davy says, a wire-gauze having 576 apertures to the square inch is safe, under all circumstances. At p. 41, he says, gauze with 625 apertures is safe; and at p. 16 he says, one with 784 apertures is safe. I have tried lamps with much finer wiregauze cylinders than those used to-day, and have found the flame readily passes. If two wire-gauze cylinders be employed, the experiment occupies a little more time, but the flame readily passes.

Do you consider those experiments to have proved satisfactorily that the Davy-lamps are not what they profess to be, safety-lamps?Yes. I beg to mention, in corroboration of this opinion, that a year or two since I inspected the gas-works at Westminster, and the man who was sent round with me showed me the safety-lamps used there, and which were made on Davy's principle. On asking him whether they ever allowed the flame to pass through them, he replied, that twice he had fired jets of gas by them. The circumstances under which this took place he stated to be as follows:-he was accustomed to exaInine the condition of the gasometers every night, and twice in walking round them with a Davy-lamp in his hand he had fired a jet of gas issuing from an aperture in the gasometer. On mentioning the circumstance, he stated he had been blamed for having used an imperfect lamp, but he could not discover any imperfection in it.

I believe you have a lamp before you, which, in addition to the gauze, has a glass cylinder inside?-Yes, there are several of these on the table. Here is one of Stephen. son's lamps, which is marked No. 4.

In what particular does that lamp vary in its construction from the lamp you have just been using? Is the air admitted from below?-The air seems to be admitted beneath this rim at the lower part. This lamp is locked, and therefore I cannot light the lamp to try it; but here is another, of the same kind and make, which is not locked.

Is the air admitted in precisely the same way?—Yes, as far as I can judge.