to a vertical discharge of from 60 to 70 feet. These figures are given as a guide, but may be modified by circumstances. The length of horizontal suction and discharge is not very material if sufficient size of pipe be employed to obviate the friction.

The steam pressure at the pump for lifts from 20 to 40 feet should not be less than from 20 to 30 lbs. per square inch, and for lifts from 40 to 80 feet not less than from 30 to 50 lbs.; for higher lifts greater steam pressure is necessary. For low lifts the pulsometer can be worked with exhaust steam.

The Pulsometer may render most useful service in draining the underground workings of water, of a very dirty or gritty nature, as shown in Fig. 314. For this purpose it is mounted on a frame running on wheels to suit the gauge of roadway. The steam-pipe is laid from the boilers to it, which may be at the surface. The discharge pipe is taken to the pit sump, or if that be at too great a vertical height, to an intermediate lodge-room or into the suction pipe of an upper pulsometer from which it is afterwards pumped on. The absence of exhaust steam, and the regularity of its working without constant attention, are strong recommendations to its use.

In the simple pulsometer it is impossible to obtain an expansive action of the steam, because the upper valve, whether a ball or other contrivance, must, from its construction, be allowing steam to pass into one or other chamber during the whole time the pump is at work. Where the work is constant, and there is a good margin between the pressure of steam and the pressure of water in the column, pulsometers (more particularly those above No. 4 size) may have the "Grel" automatic cut-off arrangement, which is patented by the Pulsometer Engineering Company. An economy of from 40 to 50 per cent. of the total steam consumption is said to be effected by this arrangement, which depends on the employment of a secondary cut-off valve, in addition to the distributing valve, so that a long interval may intervene between each pulsation, during which no steam can pass through the steam-pipe, although the work of pumping is going on continuously.

Question 78. Suppose a sinking pit to be 200 yards deep and a barrel in the form of a frustum of cone, whose inner dimensions are 4 feet deep, 42 inches diameter at bottom, and 51 inches diameter at top, making its ascent and descent every 60 seconds, coming up full every time; what quantity of water in imperial gallons and in tons will be drawn in 24 hours? And, further, supposing another barrel, whose inner dimensions are 6.75 feet deep, 57 inches diameter at bottom and 45 inches diameter at top, making the same descents in the same time, the pit being the same depth as the one above described; what quantity of water would be drawn in one week from the pit in imperial gallons and tons?

Let D= diameter of water-barrel at top in feet.

d=
h = height

C =

capacity

in cubic feet.

Then c = · { (D2+d2) + (D. d)} h ×·2618 (1)

if we denote the capacity of the barrel in imperial gallons by "g" then Hence is obtained

g = 6.24 x C.

g = {(D2 + d2) + (D. d) } h × 1·632 (2)

Again, to find the weight of water contained in the barrel, let "w" denote the weight in cwts.; then

Applying (2)

W =

{(D2 + d2) + (D. d) } h× 14571 (3)

8 = {(4·252 + 3'5o) + (4°25 × 3′5) } 4'5 × 1·632 = 331:85

As the capacity of the barrel is 33185 gallons there would be wound in 24 hours, 33185 x 24 x 60 = 477,864 gallons, or expressed in tons. 477,864 =2,133 32 tons, which might have been found by formula (3). Applying (2) to the second example

224

g=

{(3.75 +4'75) + (3'75 × 4'75)} 6.75 × 1632 599'68 gallons as the capacity of the barrel : therefore, in a week of 6 days there would be hauled 599'68 × 24 × 60 × 6 = 5,181,235 2 gallons or expressed in tons 5,181,235 2 23,1305 tons, or the same result may be got by applying formula (3).

224

Question 79.-The water in a pit is hauled up the shaft 350 yards deep in two tanks each holding 350 gallons, one ascending, the other descending; what horse-power is the engine which delivers a tank of water every three minutes at the surface not including the time of stoppage?

The speed of the load is 350 feet per minute and its weight 350 × 10 =

3,500 lbs. ... 350 x 3,500 = 37i2 effective horse-power according to the work

33,000

done, and assuming the engine yields 50 per cent. of effective work the horsepower of the engine would be as 50: 100 :: 37′iż: 74° 24 or 74°24 horse-power.

Question 80.-What are the special advantages and disadvantages of steam pumping-engines placed underground?

The principal advantages are,-a great saving of cost and maintenance, less room is taken up in the shaft, simplicity in construction, and an equal flow of water in the pipes. The disadvantages are, danger of flooding arising from a breakdown of the engine and access to it thus prevented, and it is not suitable for depths below 150 or 160 fathoms.

Question 81.-Upon what principle does the action of the lifting pump depend, and which is the proper position for the bucket to be placed in? The action of the pump depends upon atmospheric pressure which is equal to the weight of a perpendicular column of water 34 feet high. On the bucket being drawn up in the working barrel its tendency is to form a vacuum beneath it. But the atmospheric pressure causes the water to fill such vacuum and follow the bucket for a distance not exceeding 34 feet. In practice the bucket must never be raised more than 32 feet above the surface of the water, the usual distance from the windbore to the bottom of the working barrel is from 9 to 12 feet, and lifting or forcing pumps are arranged so that the suction shall not exceed 20 feet in height. This allows a bucket having a 12-foot stroke (which is not often exceeded) to be as effective at the top of its stroke as at the bottom when it is close to the suction pipes.

CHAPTER X.

THE GASES MET WITH IN MINES: VENTILATION.

The Atmosphere-Specific Gravity-The Symbols of Gases-Atomic Weight-OxygenNitrogen-Carbonic Acid, or Carbonic Anhydride-Carbonic Oxide-Sulphuretted Hydrogen or Hydrogen Sulphide-Proto-carburetted Hydrogen-Blowers-Outbursts-Pressure of Firedamp in the Solid Coal-Effect of Earthquakes in Liberating Gas-Afterdamp -Explosions of Firedamp-The Diffusion of Gases-Natural Ventilation-The FurnaceThe Waterfall-The Steam Jet-The Struvé Ventilator-Nixon's Ventilator-The Fabry Ventilator-The Lemielle Ventilator-Cook's Ventilator-Root's Ventilator-Guibal FanWaddle Fan-The Schiele Fan-The Capell Fan-The Medium Fan-Fan Arrangement for a Winding Shaft-Two Separate Engines to Drive Fan-Duplicate Fan and Engine -Ascensional Ventilation-Stoppings to Direct the Underground Air-currents-Advantages of Air-splitting-Regulators-Doors on Travelling Roads-Air-crossings-BratticeVelocities of Air-currents in the Roads and Shafts-Relative Sizes of Downcast and Upcast Shafts-Anemometer and Measuring the Volumes of Air-Thermometer-Barometer-Effect of Diminished Atmospheric Pressure in Seams yielding Firedamp-Barometric Rules-Water-gauge--Motive Column and Rule to ascertain it-Horse-power of Ventilation-Useful Effect of Ventilating Fans-Theoretical Quantities of Air displaced by Fans-Rules for Total Volumes of Air required at Collieries.

THE atmosphere which surrounds our globe is a mixture of certain gases, chiefly oxygen and nitrogen; these gases are not chemically combined, but are

merely a mechanical mixture, nevertheless the atmosphere is exceedingly uniform in constitution.

A chemical combination occurs when two substances unite to form something_distinctly new in character. This is not the case with atmospheric air, for, as will be shown later, after the oxygen has been eliminated from it by means of phosphorus, the nitrogen left is not affected by the operation.

The same two gases, viz., oxygen and nitrogen, may be made to combine chemically, and as a result the product is totally different from either. Fig. 315 shows this. The flask B contains a small portion of the white salt known as nitrate of ammonia, which is a combination of nitrogen, oxygen, and hydrogen in certain proportions. On applying heat the hydrogen and part of the oxygen combine to form water which runs into the test-tube A. The remainder of the oxygen combines with the nitrogen and passes off as gas to the pneumatic

Fig. 315.-EXPERIMENT FOR OBTAINING LAUGhing Gas.

trough. This is nitrous oxide or laughing-gas, as it is commonly called. It is largely used by dentists and in minor surgical operations as a safe and convenient anæsthetic. So that while a mechanical union of two elements supplies the air we breathe, a chemical union of the same elements produces an intoxicating gas, which unless used with discretion is an actual poison.

The mixture forming air consists almost entirely of the two gases, oxygen and nitrogen, in the proportion of about 4 volumes of nitrogen to 1 of oxygen, the chief use of the nitrogen being to dilute the oxygen. The composition of air is

but it slightly varies in composition; still it is usual to consider the proportion of oxygen as th and that of nitrogen as ths of the volume of the air. Besides these two gases, watery vapour and carbonic acid gas form part of the atmosphere, the former being a very variable quantity, dependent upon temperature, so that it is influenced by season, latitude, &c.; the latter is generally present in the proportion of Too of the whole volume of the atmosphere. Very minute quantities of ammonia and nitric acid are present in the atmosphere, as well as traces of light carburetted hydrogen and the different volatile compounds which are evolved at the earth's surface, and in towns traces of sulphuretted hydrogen and sulphurous acid also.

A proof of the fact that air is not a chemical compound lies in the fact that if 4 volumes of nitrogen and 1 of oxygen be mixed, there will be as a result 5 volumes of air without any alteration in temperature. In all cases where chemical combination takes place, there is as a result either an alteration in volume or temperature, or both. It is the oxygen of the air that supports the respiration of animals. The height of the atmosphere is about 45 miles, that is, our globe is enclosed by a covering of air which is uniformly 45 miles thick. Some authorities take it at 50 miles and some maintain that even that is not the limit; the point is therefore not definitely defined and it is not a material one to consider here. The density of the air diminishes as we recede from the earth, the lower strata being compressed by those above them, so that they contain within the same volume a much greater weight of air. The air is not warmed by the passage of the sun's rays through it, but when the rays reach the ground they are absorbed and raise its temperature, and this heat is radiated into the lower strata of air resting on the earth. The specific gravity of air, taken as 1 or 1,000, is employed as a standard of comparison for the specific gravities of gases and vapours. It is 815 times lighter than water and 11,000 times lighter than mercury. Its pressure at the level of the sea is equal in amount to 14'73 pounds on each square inch, or to the weight of a column of mercury 30 inches high, or one of water nearly 34 feet high. This pressure varies even at the same levels and the barometer is used to measure these variations. A cubic inch of mercury weighs 491 lb., from which we get 30 x 491 = 14'73 lbs., the atmospheric pressure.

There is no difference in the composition of the air in one part of the world as compared with another, nor in that obtained from the greatest elevations reached by balloons compared with the lowest valley.

Air is an elastic body. If it or any gas (as they have the same physical properties) be confined in a vessel, it exerts a pressure against the sides altogether apart from its weight, and the pressure is exerted on the upper part of the vessel as well as the lower. If the volume occupied by it be in any way diminished,

that is, if the same quantity is made to occupy a smaller space, the pressure will be increased, or if the space occupied remain the same, and the temperature be raised, the pressure will also be increased.

Air is compressible. Boyle and Mariotte's law of compression is:-The temperature remaining the same, the volume of a given quantity of gas varies inversely as the pressure which it bears. The law showing the relation between the temperature and the volume of any gas was discovered by Charles and may be stated as follows:-If any gas be allowed to expand freely under a constant pressure, its increase of volume when raised from 32° F. to 212° F. will be equal to o 366 of its original volume, and this law of increase holds true in the same proportion for intermediate temperatures. From this it follows that as the difference between 212 and 32 is 180, then th of 366 or about, (strictly 1 or 00203) is the expansion for each degree, and this fraction is taken as the co-efficient of expansion. In other words a gas expands of its volume at 320, or of its volume at o° for each degree that it is raised above that point. Supposing such a question as the following be given:-A quantity of gas is measured at a temperature of 70° and is found to occupy 400 cubic inches, what is its volume at 60°? To find the proportion between the space a gas occupies at 60° and 70° of Fahrenheit's thermometer, 492 cubic inches at 32° occupy 520 at 60° and 530 at 70°. The volumes therefore for any other quantity must be in this proportion, and therefore 400 cubic inches at 70° will occupy a volume at 60° in proportion as 530 is to 520. As 530: 520 :: 400: 392 4 cubic 70 60 inches; or say that of the volume at 60° = 400 at 70°, and there460 + 60 fore 400 ÷ 110% = 392'4. But this is assuming the pressure to be the same in each case; if not, a correction must be made for it. For instance, if in the above example the barometer stood at 30 inches when the 400 cubic inches of gas were at a temperature of 70° but at 29 inches when at 60°, the correction for the difference in pressure would be made thus:-As 29: 30: 392'4: 406; or it may be expressed thus, 400 x 30 x (60 + 460) =406. Or, expressing these rules 29 × (70 + 460) as formulæ; if v be the volume of any given weight of elastic fluid under any pressure and at 32° F., the volume v1 which it will occupy under the same pressure and at any other temperature of F. will be v1 = v + v × •00203 (t This will be true if the ratio of the relative volumes be put u and u1 instead of the ratio of the absolute volumes v and v1,

1

น

thus :

น

=

32).

1+00203 (32) I +00203 (1-32)

1 + 00203 (70 32) and u = 9814 X 400 = 392'5.

The formula to find the relative volumes when both temperature and pressure change at the same time is:

1 + ·00203 († — 32), and applying this to the question in

1 + ·00203 (12 — 32)

30

1 + 00203 (60 — 32)

29 I+00203 (70-32)

u = 4138 × 9814 = 406.

When the atmosphere is charged with moisture the mercury falls, because the pressure on the exposed surface is reduced. At first, to the student who remembers that water is about 815 times heavier than air, it will appear strange that air saturated with moisture should weigh less than air in a dry state.

Dry air is heavier than air impregnated with vapours, because of the extreme