in that of all others, where buyers and sellers meet on common ground.

With these principles the business of gas-lighting should be ranked among our permanent industries, and entitled to the same consideration as that of any other legitimate business. By following out strictly these principles of doing business, we shall command the confidence of fair-minded men in all communities, and with which we must endure the attacks of all others.

I think I do not assume too much when I say that the officers and managers of the gas companies, in all parts of our country, are composed of men at least as respectable and honorable as are to be found in any other branch of business. I have had personal intercourse with a large number of gas companies, and correspondence with many more, in this country and in Europe, and I have always found their officers and managers men of character and intellect, and of high moral standing in their communities. Certainly no other profession exhibits less of the demoralization of character in the transaction of general business, than

ours.

For this I claim nothing, for every man of any corporation should do right to the community from which it derives its business and patronage; but I do claim that in all the qualities which make good men and good citizens, the officers and managers of gas companies are at least the peers of all others. Let us in the justice and fairness of our business with the public, keep these principles constantly in view in the future as I feel assured we have done in the past.

The President- I am very sure every member of the Association will feel very grateful to Mr. Steele for the very able paper he has read to us.

Mr. Rankin-I move a vote of thanks be tendered to Mr. Steele for his address. Adopted.

Mr. McIlhenny-I desire to qualify a statement that I made before the recess, that the intellectual part of the

proceedings of the New England Association did not strike me very forcibly. I meant that with regard to the general proceedings at the time, and not to the individuals. At the last meeting of this Association, I promised to submit some remarks upon a subject I have taken a great deal of interest in, and I now comply with promise.

DEPOSITION OF CARBON IN RETORTS AND MEANS OF PREVENTING IT.

BY GEORGE A. McILHENNY, Engineer of the Wash ington Gas-Light Company, District of Columbia.

Mr. President: The subject on which I propose to make a few remarks, is the deposit of carbon in retorts, and the means of preventing it. This subject, although perhaps the most important connected with the manufacture of gas from coal, has received the least consideration, but I am pleased to say that within the past few years more interest has been, and is being manifested.

The accumulation of carbon as an incrustation on the inside of retorts, commences with the distillation of coal for making gas, and no means has as yet been devised to entirely prevent it. Why it is that this subject has not received more attention has often astonished me. It cannot be that it could be forgotten by any manager of a retort house, who gave that part of his duties even a passing notice; because it is ever present, and its growth is a sure crop; it is like a vigorous cancer with regard to its constant growth and certain return. It may be called the pest of the retort house and the torment of the engineer.

When it is removed it is sure to return, and again and again has this process of removal got to be repeated; in fact, it is as much of a duty and custom in some works as to draw and charge the retorts, and almost as important. Why this indifference, apparent

or real, towards a subject involving so much pecuniary interest? The only way that I have ever been able to account for it is the fact of the difficulties that stared every one in the face, without having the means to overcome them, and the natural tendency of men to shrink from difficulties that they have no reasonable hope of overcoming and another class of men do not even take the trouble to inquire into this subject, but go on from year to year cleaning out their retorts, simply because it is the custom to do so in other places, and has been in theirs; and if I may be permitted so to say—this practice of carrying the corn to the mill in the manner of our forefathers, is too prevalent in some gas works at the present time. The cause of the deposit of carbon in heated retorts is attributable to the fact, that when bituminous coal is subjected to destructive distillation by heat, it yields a great variety of vapors, and gases composed chemically of carbon and hydrogen; and having each one its particular condensing temperature, or degree of heat at which it changes from the aeriform to the liquid state, some of these having so low a condensing temperature that they remain gaseous when exposed to intense cold, while others require a considerable elevation of temperature to cause them to assume rapidly the condition of a gas; but there is another agency beside heat that can produce the condensation of these aeriform bodies, or make the liquid ones take on gaseous state, the temperature being the same; and this agency is mechanical pressure, and therefore these two agencies-heat and pressure-may co-operate, or antagonize one another.

The greater the pressure under which distillation takes place, the greater degree of heat will be required to effect the vaporization; and conversely, the gaseous condition can be produced at a lower temperature, by lowering the pressure in the retorts.

If the volatile fluid and solid substances produced by distilling coal were placed in a pure state, or unmixed

with other bodies in a retort, and heated properly, they would distil over and leave no residue in the retort; but if they were intimately mixed with some poor conductor of heat like clay, and then subjected in a retort to a quick action of the fire, some parts of the mass would become much more highly heated than others; the portion in contact with the retort, and the vapors from this part tend to be disengaged, but as these vapors would meet with great pressure from the superincumbent and comparatively cool part of the mixture, they would tend to be recondensed and some only would escape.

The temperature still rising, a change would at length occur from this cause, and in the chemical affinities of the molecules of the volatile bodies, and new combinations would take place, in which a portion of the carbon —as that constituent which has the greatest tendency to be fixed-would separate and remain chemically uncombined, thoroughly disseminated intimately in a mechanical way among the particles of clay. Now, if the pressure in the retort and the heat should be sufficient, exactly what takes place in the interior of the mass would take place at the sides of the retort, where the vapors in a greater or less condition of rarity come in contact with the heated surface. The chemical affinities would be changed under the influence of the heat. New combinations would occur, in which, by the law of definite proportions, fewer atoms of carbon would be required; and the superabundant atoms of carbon would then be deposited in a state of great purity and close aggregation.

The volatile compounds of hydrogen and carbon in coal are the only portion yielding gas capable of giving light when burnt. Now it is well known that when the coal or any similar organic matter is distilled under a low heat, that the carbon has a disposition to pass off with little hydrogen. This gas will be rich in carbon, but as the temperature rises the liquid carbide of hydrogen diminishes in quantity and the gaseous carbide of

hydrogen increases. And as the heat goes on to increase, the hydrogen continues to increase, and the carbon to diminish; or, the gas becomes richer in hydrogen and poorer in carbon. It is evident, therefore, that the deposit of carbon is caused by the combined agency of heat and mechanical pressure, the latter being the most powerful of the two.

It is well known to many persons here, that in 1867 I contrived a means to prevent to as great an extent as possible the deposit of carbon in retorts. This is known as "McIlhenny's Vacuum Process." Previous to this, I, like many others that were trying to make the retorts and coal yield good results, had a great deal of trouble from the accumulation of carbon. And knowing that successful experiments had been made by reducing the depth of the seal on the dip-pipes, I came to the conclusion that if the retorts could be worked without the seal, but very little carbon would be deposited. The theory on this subject to me is a very simple one, because it is manifest that if the gas can be removed whilst it remains in a state of vaporization, the carbon cannot be separated from the hydrogen. And it is a well-known law of organic chemistry, that the higher the temperature and the more advanced the decomposition of the substances, the simpler are the products. The affinity between the carbon and hydrogen seems to diminish. It would then be the natural tendency of the carbon to adhere to the heated surface of the retorts; but if the whole mass is removed before any separation takes place, very little will stick. In order, therefore, to remove all obstructions from a free flow of this mass of vapors, it is necessary to have the mouths of the dip-pipes perfectly free from obstruction.

Clegg says in his fourth edition, page 38, "that it is evident that the value of the gaseous and liquid hydrocarbons as light-yielding materials, is in direct proportion to the quantity of carbon contained in a given vol

ume.

The densest of the gases or vapors are therefore