Page:Library Construction, Architecture, Fittings, and Furniture.djvu/57

Rh maintenance of a definite proportion between the warmth of the internal and external air, which demanded a reduction of the temperature to about 45° F. The attendant replied that his theory might be excellent, but he was sure that if he reduced the temperature to that point he* would have his readers at boiling point!

In heating by hot water on the high-pressure system, small wrought iron tubes of ⅞-inch bore are carried through the room from the furnace boiler. When the fire is lit the small quantity of water is soon heated, and a very rapid circulation, giving out great heat, is speedily obtained. This system is often adopted by architects, as the pipes are small and neater in appearance than those used in low-pressure systems. Its disadvantages are the danger of bursting, as the pressure will vary from 50 to 500 lbs. on the square inch; a great liability of obstruction in the pipes through the water freezing during cold weather, when an explosion is sure to take place; and the over-heating of the air in contact with the pipes nearest the furnace, and the consequent liability to fire, if by accident wood or other inflammable substances are in contact with them.

For the low-pressure system of heating by water, pipes of from 2 to 4 inches inside diameter are used. The water leaves the furnace boiler, which is placed at the lowest part of the apparatus, at boiling point, and circulates until it returns to the boiler, where it is heated again. The advantages of the system are that the risk