II. What relation, if any, is there between the calorific value of an illuminating gas and its illuminating value when consumed in a standard luminous flame burner?

Ans. There is no definite relation between the calorific value of an illuminating gas and its illuminating value when consumed in a luminous flame burner. The greater part of

the calorific value is derived from components which do not of themselves furnish illuminating value, and by reason of change in composition it is possible for an illuminating gas to vary considerably in calorific value and yet be of the same illuminating value or to vary in illuminating power while remaining of practically the same heating value.

In the case of different samples of coal gas made from the same coal, but of different candle-powers by reason of being produced by carbonization of the coal at different temperatures, there is a fairly constant proportion between the illuminating value and the calorific value, as there is also, within certain limits of candle-power, in the case of different samples of carburetted water gas made from the same oil, but this relation does not hold between gases made from different coals or different kinds of oil.

In a lecture delivered before the Institution of Gas Engineers, Prof. V. B. Lewes gave the following table as the average relation between candle-power and calorific value. as determined by a number of tests, but said that the results in any particular case might vary 5 per cent. either way from

these, and even with this qualification exception was taken to the figures by some gas engineers. They stand, however, as the most definite statement yet published. (Trustees.)

12. Describe the method of building up the wall of a concrete gas holder tank and the precautions to be observed to insure its being water tight.

Ans. Various methods may be adopted for building a tank wall of concrete. When, as is usual, a trench is excavated around the whole circumference of the tank with an outer diameter greater than that of the outer faces of the piers, it is customary to use wooden forms made to the proper curve, one concave for the outer face and one convex for the inner face of the wall, from 2 feet 6 inches to 3 feet high, and of a convenient length, usually that between two piers. These forms being set on the circumferences of the outer and inner faces of the wall, and properly supported and braced, the concrete is put in place between them and thoroughly tamped. When it has become sufficiently set, the forms are moved to the portion of the wall that is to be next made. For the piers rectangular boxes of the proper size are used in the same manner. A paper read by Mr. C. W. Andrews, before the Ohio Gas Light Association, in 1899 (American Gas Light Journal, Vol. LXX, page 445; Progressive Age, Vol. XVII, page 125), describes very fully the construction of a concrete tank by this method, and should be read by the students.

When the ground is firm and can be securely held by timbering, laid out so that small sections of it can be removed just ahead of the concrete work, as the wall is built up, the outer edge of the excavation can be made vertical and to the proper circle for the outside of the wall at its base, and the concrete tamped between the earth and an inner form. In this way a backing of undisturbed earth is obtained at the bottom of the wall that must of necessity be much more solid than any back filling. When the offset in the wall is reached, an outer form must be used, and the space between wall and earth filled in as usual, but even here the space to be filled is much smaller and the backing that much stronger.

Mr. V. Wyatt, an English constructing gas engineer of great

experience, advocated and used a method for building the walls of large tanks in concrete blocks of the full vertical height of the wall and with radial sides. Each pier formed one block, and each bay between the piers was divided into three. The idea was that, it being cheaper to sink say 48 comparatively small pits than it was to dig and brace a large circular trench, there would be a saving in the cost of the tank. The piers were first put in, the work being carried on on all four quarters of the circle at the same time, then the blocks forming the centres of the bays, and then the two blocks necessary to complete each bay. In each case the excavation was made of just the right shape and size for the wall at the bottom, and timbered in such a way that sections of the timbering three feet high could be removed as the concrete was put in, and the concrete put in in layers three feet deep, filling up the whole space of the excavation at the bottom. When the offset at the back of the wall was reached, a form was used for the back and the concrete tamped between this form and the inner face of the excavation, the space occupied by the form being afterward filled in with earth tightly tamped. All of the sections were made with radial sides and keyed into each other to prevent leakage. Thus the wall, when finished, was a circular arch formed of large blocks. Hoop iron was used, a layer of strips 6" apart horizontally being placed every 5 or 6' vertically, the ends being left projecting and turned up in the piers and centre blocks to be turned down and built in the connecting blocks, thus forming a bond between the blocks. After the wall was finished, the excavation of the centre was carried on without any need of timbering. Mr. Wyatt's paper can be found in the American Gas Light Journal, Vol. L, May 20th, 1889, page 655.

In this case the wall was made water-tight by a lining of 9 inches of brickwork, built so as to leave a space of 2 inches between the outer circumference of the brickwork and the inner circumference of the concrete, this space being grouted with Portland cement as the wall was built.

However, if care is taken to use nothing but sharp, washed sand for the mortar, and for the aggregate, materials free from loam and dirt, and of such size or sizes as to prevent the

existence of any large spaces between the different pieces, and if the mortar and aggregate are in proper proportions and well mixed, and the concrete is put into place carefully and well tamped, the wall will be water-tight without any further treatment.

If these precautions are not taken, then the wall should be rendered with 4 inch to 1⁄2 inch of neat Portland cement, or lined and grouted as above. The lining, while it is more expensive, protects the cement from the action of the water in the tank and the weather, and thus prevents any cracking and possible leakage. Such a lining should, of course, be tied to the concrete wall at proper intervals. (Trustees.)

I.

THIRD SERIES OF QUESTIONS SECTION OF 1909-
PRACTICAL CLASS-AMERICAN GAS LIGHT
ASSOCIATION.

To what state of physical subdivision is it advisable to reduce gas coal before charging it into the retorts, in order to secure the best possible results as to yield of gas per pound of coal and per retort? Give the reasons for your answer.

2. Give a description, illustrated by sketches, of a generator furnace, either full depth or half depth, as applied to the heating of coal gas retorts. Pay particular attention to the points at which the primary and secondary air supplies are admitted, and the arrangements for filling the furnace, cleaning the fire and providing the steam. required to keep the clinker soft, and do not omit sketches.

3. Give a description, illustrated by a sketch, showing a vertical section of the apparatus, of the construction of a double superheater Lowe carburetted water gas apparatus, and give a brief description of its operation for the manufacture of carburetted water gas.

4. Describe two forms of positive rotary exhausters commonly employed to draw gas from the retorts, or relief holder, and force it through the rest of the apparatus.

5. Using the weights per cubic foot of the various gases given in the answer to Question No. 6 Second Series, and the definition of specific gravity given in the answer to Question No. 5, Second Series, calculate (1) the weight of 1,000 cubic feet of coal gas with a specific gravity of .430; (2) the weight of 1,000 cubic feet of water gas with a specific gravity of .640; (3) the specific gravity of marsh gas (CH4), and (4) the specific gravity of ethylene (CH). Give your calculations in each case.

6.

In a gas pipe, one end of which is higher than the other, such as the riser pipe in a house or a street main running up hill, and in which there is no flow of gas for the time being, the pressure as shown by a syphon pressure gauge will not be the same at the top and at the bottom. At which point will it be greater? Does the specific gravity of the gas have any influence upon the amount of this difference between the pressures at the two points? Give the reasons for your answers. What are the chief commercial products obtained by the gas manufacturer from the distillation, in retorts, of a ton (2,240 lbs.) of average Pittsburg or Youghiogheny coal; what amount of each is produced and what effect has the temperature of the retorts upon these amounts? 8. What substances are employed to free gas from Ammonia (NH) and Sulphuretted Hydrogen (HS) respectively, and from Carbon Dioxide (CO) and Bisulphide of Carbon (CS) in case it is desired to remove the last two impurities?

7.

IO.

What kinds of joints are commonly employed for connecting together the separate lengths of cast iron gas. pipes? What are the respective advantages?

When globes are used in connection with flat flame gas burners, what effect does the size of the bottom opening