be sought in that main, and its position can be located by bagging at several points in succession and noting in each case the drop in pressure on each side of the bag when gas is allowed to escape from the pipe through the bag hole, the bag being put first to one side of the hole and then to the other. As long as the obstruction has not been passed the flow of gas induced in this way will cause only a slight drop on the side towards the feed, and a larger one on the side towards the district. As soon as the pipe is bagged on the district side of the obstruction the drop in pressure will be almost the same on both sides and the obstruction must be looked for between the first hole at which this is observed and the last hole at which normal conditions were found to exist. This method of bagging the mains is especially useful where no services are taken off the feed mains for some distance before the affected district is reached.

The character of the steps to be taken to remove the obstruction will depend upon its nature. If it is an accumulation of water due to a sag in the main, all that is required is the regrading of the main, while if it is a solid obstruction that cannot be removed by the use of solvents, it may be necessary to cut the main before it can be cleared. (Trustees.)

10. How would yon repair a leak resulting from a broken main? Give a full description of the fittings used and the manner in which these fittings should be applied to the main in order to make the repair complete and permanent.

Ans. The main having been uncovered and the break located, the escape of the gas should be stopped temporarily, by pressing either clay or soap into the crack. The further procedure depends upon whether the break runs around the pipe so as to be all included within not over four or five inches in length, or extends longitudinally for a greater distance than this. In the first case the repair can be made with a split sleeve; in the second, the cracked piece must be cut out and a new piece inserted.

When a split sleeve is to be used, all dirt and rust must be scraped off the pipe for a distance of a foot on each side of the break, and if the pipe has settled it must be brought back to the proper grade and alignment. A strip of unbleached

muslin, wide enough to cover the break with a margin of three or four inches on each side and long enough to wind completely around the pipe several times, is smeared with a putty made of white lead, or equal parts of white and red lead, and linseed oil and wrapped tightly around the pipe over the break. This serves to entirely prevent the escape of gas while the job is being completed. A split sleeve, that is a sleeve made. in two pieces, each of them similar in size and shape to the pieces that would be obtained by splitting a solid sleeve along a plane containing both its axis and a diameter and provided with longitudinal flanges by which they can be bolted together, is then applied so as to cover the pipe at the break and for at least three or four inches on each side of it. The joint between the split sleeve and the pipe can be satisfactorily made in various ways.

One method is to plaster the inside of each half of the sleeve with a layer of Portland cement, mixed neat, of sufficient thickness to insure the complete filling of the joint and the compacting of the cement without allowing the flanges to come face to face when the two parts are put over the pipe and drawn together by means of the bolts. Enough cement should squeeze out through the spaces between the flanges to fill them thoroughly, but if this does not occur any unfilled places can be pointed up, so that, when the job is completed and the cement has set, the two halves of the sleeves are joined together with a gas tight joint by the cement between the flanges.

Another method is to make the joints between the flanges gas tight by using strips of millboard that have been soaked in hot water until they have become soft enough to be squeezed into all the roughnesses of the faces of the flanges when the two halves of the sleeves are put in place, surrounding the pipe, and bolted together. The joint between the sleeve and the pipe is then made exactly as would be done in the case of a solid sleeve, using either lead or cement. The latter is preferable, unless the conditions are very much against its use, since making lead joints involves the carrying to every repair job of a furnace, lead pot and ladle. Drawings of two styles of split sleeves, showing their dimensions and the number of

bolts used, can be found in the Proceedings of the American Gas Light Association, Vol. XV, page 88, and on page XIV of the appendix, and also in the American Gas Light Journal, Vol. LXIX, page 712, and Progressive Age, Vol. XVI. page 529. When the break runs too far along the pipe to be properly covered by a split sleeve it is necessary to cut out the damaged portion of the pipe, making the cuts at least three or four inches beyond the furthest point reached by the crack at each end, and replace it by a new piece. To do this the main must be uncovered for a sufficient distance to enable bag holes of the proper size to be drilled and tapped far enough apart not to interfere with the work of putting in the new piece. The gas having been shut off, by means of the bags inserted in these holes, the pipe is cut at the proper points, either with a pipe cutter or by the use of diamond points and cold chisels, and a new piece of pipe of the required length cut and put in, a solid sleeve being used to make the joint where the two spigot ends come together. Before sliding the sleeve into place, the opening between the two spigot ends is covered by wrapping the pipe with unbleached muslin prepared and used as is done in connection with the repair by means of a split sleeve. Either lead or cement joints can be made in the bell and in the sleeve, but the use of cement is generally preferable for the reasons stated above. (Trustees.)

II. What are the conditions leading to efficiency of working. in a gas engine?

Ans. The essential conditions for efficiency in a gas engine

are:

1. The largest volume of cylinder with the smallest circumferential surface; in other words, the largest diameter of cylinder.

2. Maximum speed of piston.

3. Greatest possible expansion.

4. Highest possible pressure at the beginning of the explosion.

These conditions were first laid down by Beau de Rochas in 1862. They all tend to insure the least possible loss of heat from the cooling effect of the walls of the cylinder and through

the exhaust, and consequently tend to secure the greatest possible utilization of the heat produced by the combustion of the gas and therefore the greatest possible efficiency of the gas engine. (Trustees.)

12. What are the precautions that should be taken in laying fire bricks and fire clay blocks to secure for the finished work strength and ability to resist heat?

Ans. The principal precautions to be taken in laying up fire bricks or fire clay blocks are that the bricks, or blocks, should be well wetted just before they are laid in place, and that each brick, or block, should be rubbed into place in such a way as to bring its faces almost into contact with the faces of the adjacent bricks, or blocks, in the wall, the joints being made as thin as it is possible to have them, and at the same time have the fire clay fill all the interstices, so as to give a uniform bearing over the whole surface. This is especially important in the case of arches, which should be laid as nearly as possible with the blocks face to face. Bricks and small blocks can be wet by dipping them into water in a bucket, kept filled and at hand for the purpose, each piece being dipped by the mason as he picks it up for the purpose of laying it in place in the wall. The surfaces of large blocks should be wet by having water sprinkled on them, a convenient method being to employ for the sprinkling a whisk broom which is wet by being dipped into the water in the bucket. The portion of the work previously laid, upon which the bricks, or blocks, are to be placed, should also be wet in the same way.

To secure thinness of joints, those surfaces of the blocks which come together should be smooth plane surfaces, being dressed to this condition if they do not originally possess it, and the fire clay must be mixed thin rather than stiff, care being taken not to get it so thin that it will run out of the joint, nor so stiff that any excess will not be squeezed out when the block is worked into place. If the joints are not made thin, the fire clay will soften and run out of them when the work is subjected to heat, or even if it does not do this it

will shrink under the action of the heat and cause a settlement of the upper part of the brick work.

Another precaution which should be observed is that when it is necessary to cut bricks or blocks, the cut surfaces should never be exposed to the direct heat of the fire, the face so exposed being always one which has not been cut. (Trustees.)

FOURTH SERIES OF QUESTIONS-SECTION OF 1908-PRACTICAL CLASS-AMERICAN GAS LIGHT ASSOCIATION.

1. What conditions, other than the size, would determine your choice in selecting one of several kinds of anthracite coal offered for use as the generator fuel in a carburetted water gas apparatus?

2.

How do you determine when the checker brick in a carburetted water gas apparatus needs cleaning?

3. Give a description, illustrated with sketches, of one or more forms of the condensers used for cooling illuminating gas during the process of manufacture.

4. Why is it important that all tar and oily matter should. be removed from the gas before it enters the scrubbers and purifiers?

5. A two lift gas holder, the upper section of which is 140 feet in diameter, gives a pressure of 3.2 inches when uncupped, and one of 4.8 inches when cupped. What is the weight of each of the sections? Give your calculations.

6.

A gas with a specific gravity of .630 is supplied to a building 57 feet high. The gas is at rest for the time. The pressure at the ground level, as shown by a syphon gauge, is 1.5 inches. What will be the pressure shown by a guage attached to the riser pipe at the top of the building. Give your calculations. 7. In the answer to Question No. 7 of the Third Series the yield of ammoniacal liquor per net ton of coal is given