a height equal to the difference in elevation between the two ends of the pipe and that of a column of gas of the same area and height by the weight of a cubic inch of water.

In this case the difference in elevation between the ends of the pipe is 57' and the specific gravity is given as .63. A column of air one square inch in area and 57′ high will contain 57 X 12 X 1684 cubic inches, and, since the weight of a cubic inch of air is .00004418 pound, the weight of this column will be 684 X .00004418 = .0302 pound. Since the gas has a specific gravity of .63, the weight of a column of gas will be .63 times the weight of the column of air, and the difference between the weight of the column of air and that of the gas will be .37 times the weight of the column of air.

This difference will therefore be .0302 X .37 = .011174pound. The weight of a cubic inch of water is .036 pound, and the increase in pressure will be .011174 ÷ .036 = .31′′, and the pressure at the top of the pipe will be equal to the pressure at the bottom plus this difference, or to 1.5 + .3 =1.8". (Trustees.)

7. In answer to Question No. 7 of the third Series, the yield of ammoniacal liquor per net ton of coal is given at 27 gallons of from 8 to 10 ounce strength. How many pounds of pure ammonia gas, NH, does this amount of liquor represent?

Ans. Since the term ounce as used in designating the strength of ammoniacal liquor means that a gallon of the liquor contains for each ounce strength the quantity of pureammonia that will neutralize one ounce of pure monohydrated sulphuric acid (H,SO,) with a specific gravity of 1.84, each. gallon of 8 to 10 ounce liquor will contain an amount of ammonia that will neutralize 8 to 10 ounces of sulphuric acid.

The reaction between ammonia (NH ̧) and sulphuric acid (H,SO,) takes place according to the following equation, 2NH3+H2SO, = (NH,),SO,. The proportions by weight in which substances combine with each other can be determined from the molecular weights shown by the equation to enter into the reaction according to which the combination

takes place. As the atomic weight of Nitrogen (N) is 14, that of Hydrogen (H) 1, that of Sulphur (S) 32 and that of Oxygen (O) 16, the proportion by weight in which ammonia and sulphuric acid combine will be 2(14+3)=34 parts of ammonia and (2 X 1) +32 + (16 X 4) = 2 +32 + 6498 parts of sulphuric acid. One ounce of the latter will therefore combine with = 0.3469 ounce of the former, and ammoniacal liquor will contain 0.3469 ounce of ammonia per gallon for each ounce of its strength. Or in other words, the number of ounces of ammonia contained in a given number of gallons of ammoniacal liquor of a given strength is equal to the continued product of the number of gallons, the strength in ounces and 0.3469.

=

=

27 gallons of 8 ounce liquor will therefore contain 27 × 8 X 0.3469 216 X 0.3469 74.93 ounces or 4.68 pounds of ammonia, while 27 gallons of 10 ounce liquor will contain 27 X 10 X 0.3469 = 270 X 0.3469 pounds. (Trustees.)

93.66 ounces or 5.85

8. Give a description-illustrated with a sketch of a longitudinal section of both spigot and hub showing outside diameter of spigot, all dimensions of the hub or bell, the shape of the lead groove in the bell, and the depth and finished shape of the lead-the making of a lead joint in a 4 inch cast iron main. Give also the amount of lead and packing used and the length of time that should be required to do the work.

Ans. In making a lead joint in a 4" cast iron main, the first step in the operation, after the spigot end of one length has been inserted in the bell of the other and the length driven home, lined up and fixed in place by the tamping of a little dirt around the middle of it, is to fill solidly with packing, a portion of the joint space between the spigot and bell, the amount of space so filled being determined by the depth of lead which it is desired to have. For ordinary straight work with 4" pipe the depth of lead may be taken at 11⁄2", and the joint space will therefore be filled with packing to a point 11⁄2" back from the face of the bell.

Jute packing, either plain or tarred, is usually employed.

Packing which has been allowed to absorb a small quantity of tar can be driven tighter than plain packing; but, tar being cheaper than jute, it is hard to obtain tarred packing without more than the proper amount of tar, and for this reason plain packing is often given the preference.

A sufficient number of strands of packing should be twisted to form a rope of a diameter a trifle larger than the width of the joint space, and this should be cut into pieces of such length that the ends will come into close contact when a piece is placed around the outside of the spigot end of the pipe and pulled up tight. One of these pieces is used to lift the spigot end as it is inserted into the bell of the pipe previously laid, and is sent home with it, thus keeping the spigot central in the bell and avoiding the necessity of wedging it up after it is in place. This piece of packing is driven solidly into place in the bottom of the joint space by means of a caulking hammer and packing iron, and other pieces are inserted one at a time, the joint in each ring being put, say, one-fourth of the circumference away from the joint in the preceding ring, and each driven home, a sufficient number being used to fill the joint space to the required depth, leaving 11⁄2" for the lead. The packing must be driven hard, and the finished layer must be of uniform depth, so that the lead space will be uniform all around the pipe.

A clay roll or other form of joint runner is then placed around the spigot end of the pipe, being brought tight against the face of the bell, and so set as to leave a triangular space having its base on the pipe and its apex on the face of the bell slightly above the inside edge, which the lead can fill and thus make it certain that, when driven, the joint will be of the shape shown on the cut. Molten lead is run into the joint and this space until both are completely filled and the lead stands above the highest point on the inside edge of the bell, the lead being poured in through an opening, or "gate" left on top of the pipe. When the lead has hardened, the joint runner is removed and the "gate" or lump of lead where the opening for pouring was made is cut off. The lead is then chiseled all around the pipe with a cold chisel and caulking hammer. This separates the lead from the surface of the pipe

and makes a groove in which the first caulking tool, the face of which is about" thick, can fit. The lead is driven all around with this tool and then with tools successively increas

Section of 4in. Bell, Spigot and Lead Joint,

American Gas Light Associciation Standard,

NOTE-Cut shows standard in use at time answer was prepared.

ing in thickness about " until the full width of the joint has been reached. The work with each tool should be begun at

the bottom of the pipe and carried around each way finishing up at the top. The thickness of the last tool used should not be greater than the width of the joint, and the driving with this tool should cut the lead off sharp with the inside edge of the bell, otherwise there is danger that the force of the blows will be expended against the face of the bell instead of doing the full amount of work that it should do in compressing the lead in the joint. In order to have the tools fit the joints exactly, it is well to have them made in sizes varying in thickness", though it is only necessary to use on any joint tools varying by %", the proper sizes being selected. The position in which the tools are naturally held when caulking the joint will give it the finished shape shown on the cut, if the joint runner has been put on properly and sufficient lead is used.

There will be required for making a 4′′ lead joint about 4 to 5 pounds of lead, and 7 to 9 oz. of jute packing, unavoidable waste being included in each case. A good workman should be able to average nearly 5 joints an hour for a day's work.

The cut shows the spigot and bell of the standard dimensions adopted by the American Gas Light Association in 1898. (Trustees.)

9. What is a Holophane globe and how does it affect the useful light given by the source of light over which it is used?

Ans. The Holophane globe is a globe which diffuses the light from a light source enclosed by it in such a way as to make the whole surface of the globe appear luminous and at the same time changes the distribution of light in vertical planes and throws a larger proportion of the total light in the direction which will prove the most useful for any particular

case.

The diffusion of the light is effected by the combination of vertical corrugations on the interior of the globe, the effect of which is to spread the light horizontally, with horizontal prismatic mouldings on the exterior surface which spread the light vertically. The shapes of both the corrugations and the mouldings are carefully designed to secure the transmission of the largest possible percentage of the light through the glass,