By John McCrae, of Dundee.

About three years ago, when the sudden and serious fall took place in the value of the secondary products produced in gas works, many gas managers - ever desirous of doing their very best for their employers - were forced to look around for some better market in which to dispose of the products which had so seriously fallen in value. This was no easy task; and even now it forms very uphill work indeed. A comparatively new market has been created for the disposal of boiled tar at several of the German ports. But the expense and difficulty of loading ships with tar in casks take very much from the saving derived from the new manner of disposal. It occurred to me, therefore, that we must look nearer home for a remedy.

In all gas works of any magnitude, a considerable quantity of fuel must be employed for the purpose of supplying the works with steam for the exhauster engines, chemical apparatus, thawing purposes, etc. Whether this fuel consists of coke or of coal, will not in the least affect or alter my figures. I have no doubt if any manager discovers that he is working more economically by selling the coke and using a cheap small or other coal, he will adopt the cheapest process. In Dundee, where we get a good price for coke, I found, for the purpose of steam fuel, it would be far cheaper to buy small coal costing from 5s. to 5s. 6d. per ton delivered in the works, and dispose of the coke. The question of fuel then lay between coal and tar; and I have experimented somewhat extensively to ascertain the true relative values of the two classes of fuel. For the purpose of this paper, and within the last few days, I made a further examination into the question; and the results arrived at will be those here quoted. The coal we employed was what is known as Stravenhouse small coal, which costs 5s. per ton delivered. The experiment in each case lasted 48 hours. The tar employed was what is known as boiled tar; the naphtha having been previously removed, but the pitch oil left in the tar.

The value of this tar in Dundee is about 4s. per ton. The following are the figures:

Coal, 10 tons 16 cwt., at 5s.£2140
Tar, 1,460 gallons (or 9 tons 3 cwt. 160 gallons = 1 ton), at 4s. 1167
- - - - -
Saving per day by using tar.£0175

And this at the longest day, when we are using a mere fraction of steam, as compared with our winter requirements, and consequently the profit is proportionally less than it will be when we are in full work.

coal tar burner

And now allow me to direct your attention for a short time to the appliance made use of in accomplishing this tar burning. On the wall is shown a diagram giving in detail the injector known as C. & W. Walker's patent tar sprayer burner; and it is supplied only by that firm. The tar, which has been brought forward to the boilers in a thoroughly liquid state, is discharged from the center of the injector into the furnace of the boiler. Surrounding the center nozzle of the injector is an annular space through which high pressure steam passes, also into the furnace. The meaning of this steam moving along with the tar is to force a draught, as well as to raise the temperature of the tar, and so partially convert the tar into vapor; thereby making the combustion more complete. The flow of the tar is regulated by the very delicate sluices attached to the injectors. These valves consist of elongated cones and plugs, and are constructed not only for the purpose of regulating the flow of tar, but also for removing any obstruction or incrustation which may accumulate in the nozzle.

In order to keep the tar in a liquid state (which in the winter time is not an easy matter), a small steam pipe is passed through the center of the tar pipe; but, of course, no steam is discharged among the tar, as the presence of water in the injector prevents its correct working. The steam pipe is simply passed through the tar pipe, and a steam trap attached to its end. In changing from the coal or coke fuel to the tar, little or no difficulty is experienced, and very rarely is a shovelful of any kind of solid material required. The furnace bars have only to be kept covered to prevent the waste of tar and the too rapid ingress of air; and when the furnaces are in full work, and being well and carefully attended to, the tar will be found to have been nearly all consumed before reaching the solid material covering the bars. The action is very much the same as in the paraffin oil lamp. The wick is the medium by which the oil is brought to the point of combustion, where it is developed into light; but the wick remains little injured, although in close proximity to such intense heat. The oil burns, not the wick.

In the tar furnace, the tar itself burns, and the tar only.

It will be easily understood that a little experience is necessary to enable the attendant to fully understand the quantity of tar by which complete combustion is to be obtained, and which in no case must be exceeded. The moment one atom of tar is sent into the furnace beyond that which can be thoroughly consumed, you have then the most hideous discharge of black smoke (carbon) which it is difficult to describe, but which can be easily understood, and, I believe, can be seen within a few miles of where we now sit. I should mention that the injectors are fitted on the furnace doors; but the connections are of such a nature that the doors can be opened without disturbing any of the permanent fittings.

And now I have told you that the results detailed in this short paper were those obtained in the Dundee gas works. This is so; but were I to leave the matter here, it might be inferred that I considered similar results might be obtained in any and every gas works. I would not mislead you; and therefore must detain you for a few moments longer in order to show you how my town is different from many others. Dundee is very peculiarly situated in this respect. It is a long distance from any tar distiller's works capable of dealing with the large quantity of tar we have for sale during the winter. A large portion of the value of our tar must, therefore, go to the railway company, to cover the cost of transit between the two points, and so the tar distiller can allow us but a small figure for it at the starting point. Then again, Dundee being far distant from the coal fields, the coal is exceptionally high in price. I quite believe that in many of the west country towns the coal for which we are paying 5s. per ton could be had for 3s.; and the tar for which we are receiving 4s. per ton, they would get not much under the double of this. Therefore, you see, in a place so circumstanced, the figures I have given would be most misleading.

Still, I doubt not there are places as badly situated as Dundee; and it is to such places that my remarks are directed. I believe also that, in many towns distant from collieries, the tar might be sold to manufacturers for use in their steam boilers; and such an arrangement would, I think, prove advantageous both to the seller and the user of this liquid fuel.

I think that as much has been said in regard to my subject as is necessary; but permit me to add that I believe there is a future for liquid fuels. I do not say tar, but more concentrated fuels, such as crude naphthas, paraffins, and pitch oil. When you see one of our large steamers taking coal into her bunker, it must have appeared to you that there was great waste of power here. Every ton of coal laid in must require a certain amount of power to carry it; and every ton of coal so laid in reduces the cargo-carrying power to this extent. A few gallons of oil will give you the steam-producing power of a ton of coal; and this is a fact which the owners of non-paying steamships should note. Take our locomotives also. Everything I have said in regard to steamships applies to them; and the comfort to the stokers and the general reduction in labor would be very marked indeed. Of course, it may be argued that if there were such a large demand created for oils for furnaces, the old fashioned law of supply and demand might come into play, and so force up the price of the article for which the increased demand had taken place.

But I think this state of matters is rather remote, when we bear in mind the great oil wells only now becoming developed, and the oils from which can be run in bulk direct from the wells into ships, and brought to this country at very low rates. - Journal of Gas Lighting.