HYDRASTIS HYDRAULIC RAM 107 and producing on a single clump more than 1.000 heads or corymbs of flowers. In the linked States, even so far north as Boston, it will survive the winter if slightly protected by the stems being covered. Tho wild hydran- gea (H. arborescent, Linn.) is a shrub 4 to 6 Oak-leaved Hydrangea (II. quercifoUa). ft. high ; its flowers, which are borne on flat cymes, are white or yellowish, and usually all fertile, but sometimes with a row of sterile ones around the margin; the species ranges from Pennsylvania southward. The oak-leaved hydrangea (H. quercifoUa) was first discovered by Bartram in Georgia ; it was carried to Eng- land in 1803, and is the finest North American species; it has deeply lobed, oak-like leaves, and fine large corymbs of nearly white flowers, which change afterward to purple. In the gar- dens at the north is often seen the snowy-leaved hydrangea (ff. rivea, MX.), a shrub from f> to 8 ft. high, with large leaves of a silvery white- ness beneath, and flowers in terminal cymes, having a few showy, white, sterile florets en- closing many small, green, fertile ones ; it grows in the upper part of Georgia and the Caroli- nas. Within a few years several fine hydran- geas have been introduced from Japan, some of which, though they have received specific names, are varieties of ff. ffortensia-, while others are distinct; preeminent among these is ff. paniculata grandiflora (sometimes called H. deutzifolia), which is one of the finest hardy shrubs in cultivation ; it produces an oblong panicle, often a foot long, of sterile flowers, which are at first white, then gradually turn pink, and by the time frost comes they are brownish red. in DRASTIS. See PUCCOON. HYDRATES (Gr. Map, water), compounds con- taining water, or its elements in the proportion to form water. Thus lime (oxide of calcium) slaked with water forms a chemical combina- tion with a portion of this, and falls to a white powder, which is a hydrate of lime. Hydrate of potassa is a combination of potassa and water, and is permanent even when exposed to high temperature. Common oil of vitriol is also a chemical combination of water and sul- phuric anhydride. HYDRAULIC RAM, a machine for raising water by employing its own momentum, acquired by a fall, a portion of the water only being raised. The accompanying diagram, fig. 1, will serve to explain its action. An impulse pipe, H, leads from a cistern or reservoir, C, and has a fall depending on the amount of impulse re- quired, and corresponding with the other parts of the machine, and on the height the water is required to be raised. The lower end of this impulse pipe turns up at A, where there is a large valve, usually conical and opening down- ward. This valve is of such a weight that the simple pressure of the water in the cistern and pipe, or the head, will not raise it, a certain degree of momentum being required for that purpose. When the valve is open the water rushes through it and soon attains this required momentum, and the valve rises and shuts against its seat. The motion of the water in the end at A is arrested, but not entirely so in that portion of the pipe between H and the cistern, for the impulse opens the valve B and forces water into the bell-shaped chamber D, and eventually into the delivery pipe E. When the impulse of the water flowing through the valve B becomes less than the pressure upon it, the valve closes and prevents the water which has passed through from returning. The time of this flow is very short, because the ar- rest of motion of the water in the end of the impulse pipe so reduces the force exerted against the impulse valve that it falls after a brief interval, when the water again rushes out and relieves the pressure at B. But it soon acquires sufficient momentum to again raise the impulse valve, when the shock is repeated, and the acquired momentum again expends it- self principally against the valve B, and the Fio. 1. Hydraulic Earn. water ascends into the air chamber and deliv- ery pipe. The use of the air chamber is obvi- ously to produce a constant pressure in the pipe E, as nearly as practicable, and to relieve it from the sudden shock which would other- wise be caused by the shutting of the valve B.
