HYDRATES are substances in which a definite quantity of water is chemically com bined with a definite quantity of some other constituent. Although water is a per fectly indifferent substance, possessing neither acid nor basic properties, yet it enters into combination both with acids and with bases, and thus forms the bodies termed hydrates. Thus, when an acid has once been allowed to combine with water, the entire separation of the water can usually only be effected by the presence of some strong base, which displaces the water. If, for example, we distill diluted sulphuric acid,water is expelled up to a certain point, when both acid and water are distilled together. The liquid now contains one equivalent of water, and one of acid (HO,S03), and is termed hydrated sulpfitirie acid, and this equivalent of water can only be displaced by an equivalent of potash, or some other base. Hydrate of baryta (13a0,H0), hydrate of lime or slaked lime (CaO,H0), hydrate of sesquioxide of iron (Fe 03,3H0), and hydrate of oxide of copper (Cu0,H0), are similar cases, except that here the water is displaced by an acid instead of a base. The above are examples of hydrates of acids and bases or oxides. Gypsum is an example of a hydrate of a salt.
extensive use within the past few years. worked near each other, water-pressure is by far the most manageable, CCODOIlli cal, and convenient mode of working them. Sir W. Armstrong &Co., of New castle, have taken the lead in introducing this kind of machinery. They have fitted up a great many railway goods stations with complete systems of hydraulic cranes.
The figure represents one of the simplest forms of hydraulic cranes, such as are in use for loading goods in a railway sta tion. It is made entirely of iron, and consists of two upright cheeks, A, be tween which there is fixed a hydraulic ram (similar to that used in the hydraulic press), occupying the lower half of the upright frame A. The upper end of this ram carries a pulley 13. A similar pul ley is fixed to the upright frame at A. chain is secured to a bracket, D, on the upright frame. This chain passes up over the pulley 13, down and under the pulley C, and then over tile pulley E, on the end of the jib of the crane. It is obvious that the rising and falling of the ram will cause the chain, F, to ascend and descend with its load G.
The ram is forced to ascend by the admission of water under great pressure by the handle II, which serves also to allow the water to flow out after it has done its work, and the ram descends by its own weight, allowing the chain, F, to run down with or without a load 011 it.
The pressure usually employed in working hydraulic cranes is greatly in excess of the pressure admissible in the case of steam. Six or seven hundred pounds to the sq.in.
is usually employed as the working-pressure. It is got up to this great pressure by means of an arrangement called an accumulator, which consists of a large hydraulic ram of 16 or 18 in. in diameter, carrying a wrought-iron cylinder. This 'cylinder is filled with stones or gravel to the weight of 60 or 70 tons. A powerful horizontal steam engine forces water into a cylinder and slowly raises the ram with its enormous load. Pipes lend away from the cylinder to the cranes in the different parts of the station, and are thus supplied with water under the great pressure caused by the load forcing the ram into the cylinder. The load is constantly rising and falling a little as the cranes draw their supplies from the cylinder. If the cranes were supplied direct from the force pumps of the steam-engine, without the intervention of this accumulator, their action would be jerky and unsteady. The accumulator acts as a reservoir of power, and when it happens that a great number of cranes are drawing off water at the same moment, and in excess of what the engine force-pumps can supply, the ram descends, keeping up the while the full 700 lbs. pressure; and then, when the cranes are demanding less abun dant supplies, the engine overtakes its work, and sends the ram up again. When it arrives at the top it touches a lever communicating with the throttle-valve of the engine, and thus slows or stops the engine when the accumulator has mounted to its maximum height. The moment it •begins to descend, the lever is relieved, the throttle-valve opens, and the engine goes on again with such speed as the work demands.
It'is easily seen that when the pulley rises any given distance, the weight will, at the same time, rise double that distance, because it raises a double length of chain; and, in the same way, by passing the chain twice, thrice, or any greater number of times over the pulleys, the weight can be made to travel any number of times further than the ram. It is, in fact, the reverse action of a block and tackle. If the block is made to move, the fall will move further than the block in proportion to the number of times the rope passes over the sheaves. This kind of arrangement is adopted when it is desired to lift anything to a considerable height, such as, grain to upper floors of a warehouse. There is. of course, a diminution in the weight the machine can hoist, in proportion to the excess of travel of the load to that .of the ram.
The lifts, or ascending rooms, now in use in inilby large hotels, are con