those which possess the highest illuminating power." All of the members of this class, however, as just mentioned, are more or less rapidly decomposed at a red heat, and in the usual process of gas making, the inner walls of the retorts soon become covered with a layer of carbon derived from this source.

This destruction of luminiferous constituents is dependent, on the one hand, on the length of time during which they are exposed to a high temperature, and on the other, upon the number of the particles of such constituents which come in contact with the red-hot sides of the retorts.

Two methods therefore suggest themselves for the prevention of this decomposition. The first would consist of the rapid removal of the gases from the retort, and the second in the dilution of the luminous by an admixture of non-luminous constituents, for it is evident that the number of atoms of illuminating gas, in contact with a given surface, would only be half as great if that gas were diluted with an equal volume of hydrogen, as it would be without such mixture.

In speaking further on this theory, I am satisfied, and it must be apparent to any one having examined the subject, that the actual and immediate cause for the deposit of carbon in retorts, is mechanical pressure; and when that is entirely removed, but very little if any carbon will adhere. When distillation first takes place on the inside of the retort, the vapors are in a heavy black mass, containing all the volatile portion of the coal. And this vapor is at a low degree of temperature, and only separates as the mass becomes more highly heated. And in this condition the atoms of carbon become condensed, and many of them adhere to the heated walls of the retort, and of course become separated from the mass of vapors. Now, it must be evident that if this entire mass were at once and immediately removed, and passed in the ordinary way to the holder, those atoms of carbon would be carried by the

volume of hydrogen and become an illuminating agent, instead of sticking to the inside of the retorts; and when it is considered that the value of the gas for giving light is in exact proportion to the amount of carbon it contains, this matter will be appreciated.

When clay retorts were first introduced, the great difficulty in their use appeared to be the amount of carbon that accumulated, because of the greater heat under which they were worked. Owing to this fact, Mr. Grafton, at the Cambridge (England) works, commenced a series of experiments to ascertain the cause of the vast accumulation of carbon, and without going into all the details of his experiments I will simply give the results: From 67 tons of coal, 10 cwt. 24 lbs. of carbon was taken out, or 1% per cent. of the weight of the coal carbonized. This was under a pressure; but when he reduced that pressure he found the amount of carbon was very much decreased.

Mr. Smedberg has written me on this subject, and I do not consider his any mean authority. I think, therefore, that it is unnecessary for me to go any further to prove this theory, as I am sure that every intelligent gas engineer will admit it. I will now give you what has been my own experience under the operations of the "Vacuum Process."

The growth of carbon inside of retorts forms an interesting study, and doubtless there are those present who have watched its formation with interest. Although the atoms are not visible to the eye, yet the formation can be seen to increase from week to week; and if allowed to go on without being removed, it will entirely choke up the retort. The formation is continuous, but the quantity in the retorts is entirely dependent on the frequency of its removal. I have seen it on all sides and top of the retort, and hanging from the roof like rocks from a cliff. It was my custom before the use of my process, to clean out the retorts about every five weeks, but then the retort was very much impaired;

two weeks before, and often several days after, leaky, so that I calculated that about three weeks embraced the entire time when the retort had its full capacity.

Now, in working the retorts with the "Vacuum Process," I make it a rule to clean them out every three months, but then there is less carbon than there would be under a pressure in three weeks. No carbon whatever collects on the roof of the retort, nor on the sides, nor in fact any part of it where the coal does not lie.

The exposed part is just as clean as the day the retort was fired up. It collects in the corners, and increases in thickness towards the back; this is owing to the fact that the vapors cannot get away as rapidly as where the coal does not lie, consequently become decomposed. The carbon adheres to the retort, but in my opinion if there was no obstruction such as the coal is, no carbon of any account would remain. If there was no advantage derived from the use of this method of working retorts, other than the prevention of the formation of carbon, it is of great value, in a monetary sense, as well as facilitating the operations of the retort house.

What would be the feeling of relief to every manager of a gas works, if he knew he could go on and charge his retorts from the time he set them until they were burned out. It having been fully demonstrated that retorts can be run from three to six months without cleaning, thus putting within the reach of every superintendent of a gas works, the facility of having to clean out retorts from two to three times a year only, instead of ten times, as is mostly the case now.

I do not deny that the general management of a gas works may not have something to do with this subject. In fact, I think that many companies make a grave mistake when they suppose that any man who can throw coal into, and draw coke out of retorts, understands the manipulations of the materials in the manufacture of illuminating gas.

Indeed, under this delusion a great many companies

are suffering heavy loss; and some large companies, hundreds of thousands of dollars per annum. In addition to the prevention of the formation of carbon, there is a very important advantage in the increased yield from the coal. This of course will be increased just in proportion to the yield under the pressure system.

We will take for example Penn coal, and admit that the company gets 4 cubic feet per pound of coal: now if that yield can be increased to 4 cubic feet, and the company carbonizes 50,000 tons of coal per annum, the difference will be 44,800,000 cubic feet; or if the company uses 25,000 tons of coal, then the increase will be 22,400,000 cubic feet. But now, suppose the yield to be only 4 cubic feet per pound, then the difference to the company using the 50,000 tons of coal would be 89,600,000 and the company using 25,000 tons, 49,800,000 cubic feet. And so this scale goes up or down just in proportion to the amount of coal carbonized; assuming all the time that the gas be the same, or as good in quality. You will perceive, therefore, that these figures are indeed startling, but nevertheless true.

I suppose there are some present who have often wondered why it is that there is such a vast difference in the results of gas companies using the same materials, but such is the fact, there is a great difference. Now, there ought not to be much difference, because the same facilties are at the command of all.

It is true, however, that the same appreciation of the necessity of making high efforts to be at the top, and taking advantage of all the circumstances that contribute thereto, are not always realized alike. Nor is it to be supposed that all have equal abilities any more than in other professions; but notwithstanding these facts, there should not exist the differences that now do, in the results of the various companies.

You will perceive that the saving does not end with the decrease in the quantity of carbon deposited inside the retorts, nor the increase of yield from the coal, but ex

tends to all the incidental expenses of the retort house; and this saving is in exact proportion to the increased yield from the coal and retorts.

It will doubtless be asked if there is not some difficulty in working successfully under this process; and in response I will say, that all that is necessary is to thoroughly understand the principle and the means of carrying it out-and there can be no doubt of success. But I will admit that it is necessary to fully comprehend these points; but then it is to be presumed that every, or nearly every gas engineer fully understands these principles, and the mode of carrying them out. All the difficulties that encounter one in the use of this method are mechanical, and therefore easily overcome if properly understood.

I am often asked if the exhauster has not to be carefully run. Yes, if the means of controlling its actions are not perfect, or nearly so. Now, with me there is no difficulty in this respect, because I have a governor that has perfect control over the engine, and when this is obtained (which is easily done), there is no more difficulty or risk than there is in the old system.

If coal continues to be the material from which gas is made, I am satisfied that it will not be many years before this system is in general use.

On motion of Mr. White, the convention tendered a vote of thanks to Mr. McIlhenny for his address. Mr. Sibley offered the following resolution :

Resolved, That the report of the special committee on insurance be referred to the following gentlemen: Messrs. Williams, Leavenworth and Steele, to obtain charter, forms of policy of insurance, etc., and to do all other things necessary to carry into effect the proposed system of insurance, on a mutual plan.

Mr. Steele-Mr. President: I decline to serve on that committee.

The name of Mr. Clegg was inserted in the resolution, in place of that of Mr. Steele.