of ammonia, and what are the chemical reactions that occur in the process?

8. What are the products of the complete combustion of of each of the following substances?

Give in each case the weights of the products produced by the combustion of one pound of the substance, and in the case of gases give also the volumes of those produced from one cubic foot.

9. Give the heating power, in British Thermal Units, of a pound, and in the case of gases also that of a cubic foot, of each of the substances named in Question No. 8, and tell what you understand this expression "heating power" to mean.

10. How should a gas works be situated with reference to the level of the district to be supplied?

II. Give the ordinary formula for the rate of flow of gas through pipes, and calculate by means of this formula the amount of gas that can be delivered per hour through one-half mile of 8" pipe with a loss of pressure of", the specific gravity of the gas being 0.65.

12. Describe the proper method of laying bricks in cement

mortar.

(Answers to these questions are due July 1, 1906.)

ANSWERS TO SIXTH SERIES OF QUESTIOns Section OF 1908-PRACTICAL CLASS-AMERICAN GAS LIGHT ASSOCIATION.

The answer to Question No. 2 is included among the answers to the Eighth Series of Questions for the Section of 1907, and can be found on page 149 of this volume.

The answers to the other questions are as follows:

I. Is there any reason why gas coal that has been put into the coal shed of a gas works should not be left there indefinitely, if the supply is maintained so that it is not necessary to use it?

Answer. For any given gas works the answer to this question depends upon the character and qualities of the coal used. Some gas coals break up very badly when stored, the lumps becoming gradually converted into slack, and as this breaking up exposes fresh surfaces, as well as a greater surface in proportion to the volume, to the action of the air, and thus makes it easier for slow oxidation of the coal to take place, a comparatively rapid deterioration sets in and may continue until the value of the coal is practically destroyed. Under these conditions it is not advisable to keep coal in stock for any length of time, and a practice should be made of working out the oldest stock at regular and short intervals.

However, many of the gas coals used in this country, particularly those from Western Pennsylvania, do not depreciate to any great extent when stored, except on the surface of the pile, and even in this portion the loss is very small after the end of the first six months, so that such coal when stored in fairly deep piles, protected from the weather, will, even when stored for many years, suffer only a small total depreciation, the larger part of which takes place in the first year. When using coal of this kind, any stock that it is not necessary to use can be left in store indefinitely as far as loss in gas making value is concerned, since after having been stored for a year, the future depreciation on it will be much less than would be suffered by fresh coal stored in its place, and it is better to use the fresh coal, even if it is not possible to also make a saving

in cost of handling by working the fresh coal directly into the retort house instead of having to put it into and take it out of the shed.

But even when the coal does not depreciate sufficiently to call for working out old stock, it is advisable to do this every few years and clean out the shed, for the purpose of checking

the accuracy of the coal account as carried on the books, since in most coal sheds it is impossible to secure an accurate check in any other way. If, however, the coal is stored in pockets, into one of which a known quantity has been put and allowed to remain undisturbed, or if the stock pile is kept entirely separate from the rest of the coal and not drawn upon, there will be no reason for not keeping indefinitely a stock of coal of the character spoken of in the preceding paragraph, except an emergency when no other coal can be obtained. (Trustees.)

3. What is a by-pass? Give a description, illustrated with sketches, of a by-pass for two vertical, multitubular condensers.

Ans. A by-pass to any part of the apparatus of a gas works is a system of pipes and valves so arranged that by opening one or more valves, and closing others, the gas flowing may be directed either through, or past, that part of the apparatus concerned.

The preceding cut shows a by-pass for two vertical, multitubular condensers, so arranged that either one or both of them may be thrown out of action at any time without interfering with the working of any of the rest of the apparatus. When both condensers are in action, valves Nos. 1, 3, 4 and 6 are open and valves Nos. 2 and 5 are closed. To throw condenser No. 1 out of action while leaving No. 2 at work, valve No. 2 must be opened and Nos. 1 and 3 closed. Again, starting with both condensers at work, to leave No. 1 in action and throw out No. 2, valve No. 5 must be opened and Nos. 4 and 6 closed. When both condensers are to be thrown out at the same time, valves Nos. 2 and 5 must be opened and Nos. 1, 3, 4 and 6 closed. (Trustees.)

4. Give a description, illustrated by sketches, of the ordinary dry centre valve for four purifying boxes, built to put three in action at one time. Show on the sketches the divisions of the seat and cover, and describe the action of the valve.

Ans. The centre valve is a device whereby a set of four purifying boxes may be so operated that one box is thrown out of use for cleaning, the other three being in use, and the