HYDRATES 



2885 



HYDRAULIC PRESS 



produce bluish blossoms. The common hy- 

 drangea is a native of China, and was intro- 

 duced into England in 1790. The wild, or 

 American, hydrangea was brought into Euro- 

 pean cultivation from Virginia in 1796. The 

 hardier cultivated species are used in orna- 

 mental borders. The Hortensia, or Otoska, is 

 a dwarfed variety which is grown in hothouses, 

 and is popular for Easter decorations. See 

 SAXIFRAGE. 



HYDRATES, hi' dray ts. In chemistry com- 

 pounds are usually divided into three chief 

 groups, according to some characteristic prop- 

 erties they possess. These groups are known 

 as acids, bases and salts. The bases are also 

 known as hydrates, or hydroxides. A base or 

 an hydroxide contains a metal in combination 

 with oxygen and hydrogen. The oxygen and 

 hydrogen form a group called hydroxyl (sym- 

 bol OH), which in many chemical changes acts 

 like an atom. An hydroxyl contains one atom 

 of oxygen and one of hydrogen, instead of the 

 two atoms of hydrogen that enter with the 

 one of oxygen into the composition of water. 

 Hydroxyl does not exist free in nature, like 

 the elements or the compounds, but it enters 

 into many combinations. It forms part of the 

 large group of organic compounds known as 

 alcohols. 



Typical hydrates are the alkalies (see AL- 

 KALI). The name alkali refers specially to the 

 properties of these compounds, and not to their 

 chemical composition. The principal alkalies 

 are caustic soda, which is sodium hydroxide; 

 caustic potash, or potassium hydroxide; lime- 

 water, or calcium hydroxide; ammonia water, 

 or ammonia, or ammonium hydroxide. 



HYDRAULIC, hi drawl' ik, ENGINE, a ma- 

 chine to utilize the power of falling water for 

 the purpose of driving machinery, was first 

 designed by Sir William Armstrong. It is 

 most efficient when working under a full load, 

 the effectiveness decreasing with the load. 

 Three types are in use: (1) water-pressure 

 engines or motors; (2) water wheels; (3) tur- 

 bines (see WATER WHEEL; TURBINE WHEEL). 

 Strictly speaking, only the first is a true hy- 

 draulic engine. It is similar to a steam engine, 

 water under pressure being used instead of 

 steam. The water is forced into a cylinder, 

 pushing back the piston head until a sliding 

 valve is opened by which it flows out. As 

 only a small part of the water pressure is 

 used in driving the piston, there is great loss 

 of energy and these engines are relatively 

 inefficient, save when considerable power is 



wanted at low speed. These machines have 

 been largely displaced by electric motors, but 

 are still used occasionally for elevators and for 

 pumping air for pipe organs. C.R.M. 



HYDRAULIC PRESS. For one man to lift 

 hundreds of tons would seem an impossibility, 

 or at least to be a task requiring very compli- 

 cated machinery. In truth, however, a mech- 

 anism scarcely more intricate than a pump 



ONE FORM OP HYDRAULIC PRESS 

 The explanatory letters are referred to in the 

 text. 



can transform the power of the human arm into 

 enormous pressure. This mechanism is the 

 hydraulic press. Until the invention of more 

 rapidly-acting machinery it was in general use 

 for pressing cotton, paper or hay into bales; 

 for squeezing oil from cotton seeds ; for punch- 

 ing holes in steel plates and for other opera- 

 tions requiring unusual power of compression. 

 Its principle is also utilized for the hydraulic 

 elevator, in which the ordinary pressure of 

 water in city mains lifts the weight of a 

 number of people. 



A hand-power hydraulic press is shown in the 

 illustration. That part of the apparatus which 

 contains the small piston is really a force 

 pump (see PUMP) ; when the handle is pressed 

 down water or oil is forced past the valve w, 

 and the piston p is raised. Back in the seven- 

 teenth century the great physicist, Pascal, 

 whose biography will be found in these books, 

 discovered that if you exert pressure upon any 

 part of a liquid enclosed in a vessel an equal 

 pressure will be exerted upon everything which 

 the liquid touches, that is, the pressure is 

 transmitted equally in all directions. If the 

 area of the bottom of the smaller piston is 

 one square inch and the larger piston has a 

 diameter twenty-four times that of the smaller, 



