the steam condenses, and in so doing absorbs the ammonia gas in greater and greater quantity as the temperature falls, until at the outlet of the last cooler most of the ammonia has been absorbed and the concentrated liquor so formed is drawn off to the storage tank. As it is not advisable to have the temperature at the outlet of the coolers reduced to too low a point, some of the ammonia gas is still unabsorbed at this point, but is caught by the water in the absorber, this water being kept cool by circulating cold water through the coil with which the absorber is provided. The liquor thus formed in the absorber should be drawn off and replaced by fresh water as soon as it reaches a strength of 2° Twaddell.

The strength of the concentrated liquor is tested occasionally and kept at the proper point by adjusting the flow of liquor and of steam. The more steam used for the same amount of liquor the weaker is the concentrated liquor. The more weak liquor used for the same amount of steam the stronger is the concentrated liquor. If too much weak liquor, or too little steam is used, all the ammonia will not be driven off from the spent liquor, which will carry some of the ammonia out with it from the still. When this is the case, the spent liquor running off will smell of ammonia.

Some hints as to the points to be watched in starting up, operating and letting down an ammonia concentrating apparatus will be found in a paper read before the Michigan Gas Association, at its Seventh Annual Meeting, by Mr. George Osius, and published in Progressive Age, Vol. XVIII, page 90, and the American Gas Light Journal, Vol. LXXII, page 449.

The principal condition rendering it advisable to concentrate ammoniacal liquor is remoteness from a market in which this liquor can be sold. In this case the reduction in cost of transportation owing to the concentration becomes an important item in permitting the ammonia to be sold at a price that renders it worth handling. It has been stated that a works carbonizing as low as 750 tons of coal per annum can net a profit from concentrated ammonia that will pay at least 15% interest on the cost of the necessary apparatus. Of course, this figure depends somewhat on the location of the works

and upon the amount of money put into the apparatus. (Trustees.)

8. A cylindrical oil tank of the "cheese-box" type is 22' 6" in diameter and 16' o" high. How many gallons of oil will it hold for each inch and each foot of its height and what will be its total contents when full?

Ans. The area of a circle 22′ 6′′ or 270" in diameter is, as obtained from the tables of circumferences and areas of circles, 57,256 square inches, and therefore the tank will contain a volume of 57,256 cubic inches for each inch of its height. An American gallon has a volume of 231 cubic inches. 57,256÷231 247.86 or each inch in height of the tank will contain 247.86 gallons of oil.

=

Each foot in height will contain 247.86 X 12 = 2974.32 gallons, and the total contents of the tank when full will be 2974.32 X 1647,589 gallons.

Using the contents per inch and per foot, determined as above, a table should be prepared for each oil tank at a gas works, showing the total contents for any height to which it is filled with oil from 1" to the full height. (Trustees.)

9. Describe some form of calorimeter by the use of which the calorific value of gas can be determined by observation.

Ans. The calorimeter that is most commonly used in this country for determining by observation, the calorific value of gases, is an improved form of the Hartley Calorimeter, designed by Hugo Junker, and known as the Junker Calorimeter. It acts by transferring the heat developed by the combustion of a measured quantity of gas to a measured quantity of water which flows at a constant rate through the apparatus.

The calorimeter itself is an annular vessel made of two concentric copper cylinders, the outer cylinder having a diameter of about seven inches and the inner one' a diameter of about four inches. To the top of the outer cylinder is fitted a conical hood which closes the whole top of the vessel, except for a circular opening left at the apex of the cone. A smaller hood which begins as a frustrum of a cone with its base

upwards and then changes to a cone with its apex upwards, is attached to the inner cylinder so that the annular space is continued up between the two hoods and the space within the inner cylinder is shut off at the top from this annular space. The bottom of the inner cylinder is left open and the bottom of the annular space is closed by a ring. At a distance of four or five inches above this ring is fastened another ring forming a water-tight partition which divides the annular space into two compartments. Through the upper one of these two compartments pass a number of small copper tubes, the upper ends of which are fastened to the diverging cone of the inner hood while the lower ends are fastened to the partition described above. The joints between the tubes and the hood and partition must be water-tight.

Into one side of the outer cylinder, just above the bottom of the upper compartment, opens a copper pipe set at a right angle to the axis of the cylinders. This pipe enters the side outlet of a tee piece set with its run vertical and about two inches from the cylinder. From the lower outlet of the tee the pipe is dropped a short distance and then passing around a U-shaped turn rises to a height of about 20" above the top of the annular vessel and ends in a small cistern or cup formed inside of a larger one, both cups having a common support by the pipe. To the part of this bottom covered by the small cup is attached a corrugated nipple, over which a rubber tube can be slipped, and a similar nipple is fastened in the space outside of the small cup. The upper outlet of the tee is closed by a rubber cork pierced for the insertion of a thermometer. A stop cock provided with an arrow-shaped handle, moving over a graduated quadrant, is placed between the tee and the bend. Opposite the opening of the pipe in the outer cylinder is placed a baffle plate forming a small annular space extending completely around the cylinder, the object of which is to cause the water entering through the pipe to be uniformly distributed all around the annular chamber.

To the circular opening left, as described above, at the apex of the outer hood is fitted a copper tube provided with several baffle rings with centre openings. This tube ends in a tee piece, the upper end of which is closed by a cork pierced for

4

Cold Water Overflow

Cold Water Inlet

a thermometer, and from the side outlet of this tee runs a pipe which ends in and supports by its side a cup. Inside the cup is a funnel ending in a nipple for tubing, which passes through and is fastened with a water-tight joint to the bottom of the cup.

Vertical Section.

On one side of the lower compartment of the annular space is an elliptical opening leading into a tube of the same cross section. Provision is made for the insertion of a thermometer into this tube as close as possible to the outer cylinder, and it is also fitted with an ordinary stove pipe damper. At a point diametrically opposite to this tube a small tube is tapped into the bottom ring, and directly under it is tapped in a rod which serves to support the burner through which the gas is consumed.

To prevent loss of heat by radiation the whole of the body of the calorimeter above a point an inch or two below the bottom of the upper compartment is jacketed by a highly polished nickle-plated copper cylinder made sufficiently large to leave an annular air space one half inch wide between it and the calorimeter.

When set up, the apparatus stands on three removable legs provided with leveling screws. Reference to the accompanying sections of the calorimeter will, in connection with the above description, enable the construction of the apparatus to be fully understood.

Two measuring glasses are provided with the calorimeter. The larger one will hold two litres and is graduated in intervals of five cubic centimetres. The other is an ordinary Ico cubic centimetre glass, graduated to one-half of a centimetre. (A litre is 1,000 cubic centimetres and a litre of water weighs one kilogram.)

When it is desired to make a determination of the calorific value of a gas, the apparatus is set up on a firm base in such a position that it can be readily supplied with the gas to be tested and with flowing water. The thermometers provided for the purpose, which are graduated in tenths of degrees Centigrade from o° to 50°, should be inserted in the proper openings, as described above. Connection is then made to the water supply by means of rubber tubing slipped over the nipple on the bottom of the smaller inside cup, of the two supported by the pipe which enters the calorimeter at the bottom of the upper compartment. A rubber tube leading to a drain is slipped over the nipple opening from the larger cup in the space outside the small one, and another pipe is slipped.