Page:The American Cyclopædia (1879) Volume IX.djvu/116

 108 HYDRAULIC RAM The expenditure of force in this machine is obtained by multiplying the amount of water discharged at A into the head, or height of water in the cistern above the valve A. The economy of force is found by multiplying the amount of water delivered by the pipe E into the height to which it is raised. The proportion in good rams is from GO to 70 per cent. The head of water should be from 4 to 6 ft. for rais- ing water vertically 30 ft. There is a differ- ence of opinion in regard to the proportional increase of head to increase in height of the delivery pipe, and machines of different modes of construction will require variation in this particular. The height of head is, however, practically restricted in consequence of the wear and strain produced by the shock when the head is great. A practical difficulty in the machine is to preserve the necessary quantity of air in the air chamber. This is constantly being absorbed by the water, so that in time its volume becomes too small to yield sufficient elasticity. The difficulty is obviated to a great degree by the application of what is called a shifting valve, opening inward at G. There is a moment of time after the shutting of the im- pulse valve when there is in certain parts of the machine a diminution of internal pressure to a degree below that of the pressure of the atmosphere. During this moment a bubble of air will enter at G and ascend into the air chamber, but it is difficult so to regulate the supply that it will not be necessary to remove the air chamber and introduce a fresh supply of air. In large European machines there is often placed at B an inner air chamber with two valves at its base, suspended by hinges and opening laterally. The impulse pipe may be straight, and inclined as shown in the fig- ure, or have a vertical and a horizontal limb ; or it may be curved. There are several prac- tical points in regard to its size and length which should be observed in the erection -of the ram. In general, it may be stated that if the impulse pipe is very wide and short, it will not maintain a sufficient impulse to lift the water against great pressure in a long delivery Fio. 2. Wlitehurst's Machine. pipe, because of the tendency to a reactionary movement of its contents, which is prevent- ed by the resistance offered by a longer and smaller pipe. The invention of the hydraulic ram is ascribed to the elder Montgolfier, and its improvements to his son. The principle, HYDROCHLORIC ACID however, was previously employed by John Whitehurst of Cheapside in a machine con- structed by him in 1772, an account of which was published in the " Philosophical Transac- tions " in 1775. Fig. 2 is a representation of Whitehurst's machine, and it will be seen that the principal difference between it and Mont- golfler's ram is that it has a stopcock in place of the automatic impulse valve. Leading from the cistern H is a long pipe, A E, much longer in proportion than is represented in the figure, which is the impulse pipe. Its contents re- ceive momentum from the opening of the cock B, which is several feet below E. When suf- ficient force has been obtained the cock is shut, and the column of water in A B is urged by its momentum along the direct branch of the pipe G, through its depressed extremity D, into the bottom of the air chamber C. This part of the pipe contains a valve opening toward the air chamber, corresponding to the one in Mont- golfier's machine. F is the lower section of the delivery pipe. The principle of action is precisely the same in the two machines, and the explanation of the ram will answer for that of Whitehurst's machine. HYDRAULICS. See HYDROMECHANICS. HYDROCEPHALUS. See BKAIN, DISEASES OF THE, vol. Hi., p. 197. HYDROCHLORIC ACID, or Chlorohydrie Acid, a gaseous compound of one equivalent of chlo- rine and one of hydrogen (HC1), of combining proportion 36'5, long known in its aqueous solution by the names of muriatic acid, ma- rine salt, and spirit of salt, in reference to its being prepared from sea salt (murias). Priest- ley first obtained it as a gas in 1772, and Gay- Lussac, Thenard, and Davy long afterward showed that it consists of equal volumes of chlorine and hydrogen, and occupies the same space as the gases which produce it. Its ele- ments mixed together slowly combine by the action of the light, but instantly with explo- sion if exposed to the direct rays of the sun, or if an electric spark is passed through the mixture, or a lighted taper is brought in con- tact with it. The gas is obtained by adding concentrated sulphuric acid to common salt placed in a retort, and collecting over mer- cury. The chlorine of the salt (chloride of sodium) unites with the hydrogen of the sul- phuric acid, producing hydrochloric acid and acid sulphate of soda; or, by symbols, NaCl + H 3 SO4 = HCl + NaHSO,. The gas is col- orless, but escaping in the air it instantly unites with moisture present, and forms a white cloud. It has a strongly acid taste and a pungent odor. Taken into the lungs it is irrespirable, but when diluted with air is not so irritating as chlorine. It neither supports combustion nor is itself inflammable. Under a pressure of 40 atmospheres, at 50 F., it is condensed into a liquid of specific gravity T27, which dissolves bitumen. The density of the gas is 12fi9'5,'air being 1000. Its affinity for water is such that it can be kept only in jars