168 HEATING BY HOT WATER, HOT AIR, AND STEAM. 



2. Comparison of heat in water and steam. The heating of 

 horticultural buildings by steam had its day and its admirers, 

 though both are now numbered among the things that were. 

 Even if the original outlay were equal, the additional outlay for 

 fuel, the risk of explosion from neglect, and the want of perma- 

 nency in the apparatus to maintain the heat for any length of 

 time, are insuperable objections to its adoption. Among many 

 instances that could be given of this method of warming large 

 houses, we might mention the large Palm house, in the Royal 

 Botanic Garden of Edinburgh, which was erected when heating 

 by steam was in the height of its fame. This house is about 

 fifty feet high and seventy-five feet wide, in the form of an 

 octagon ; the pipes are laid around the side of the wall. There 

 is a contrivance, however, resorted to here, in connection with 

 the system, to which its success in heating the house may be 

 somewhat, if not entirely, attributed. The steam is thrown into 

 large iron boxes, loosely filled with stones and pieces of brick, 

 for the retention and absorption of the heat. These iron boxes 

 are placed underneath the shelf that surrounds the house, and 

 close by the side of the wall, and at regular distances from 

 each other. By this contrivance, the temperature .of the house 

 is kept up for a considerable time longer than would be by the 

 circulation of the steam alone. Indeed, we believe it was found 

 perfectly impracticable to maintain the proper temperature, dur- 

 ing cold nights, until this expedient was adopted, viz., of filling 

 the boxes with absorbing materials. 



We have known conservatories, in which steam apparatuses 

 had been erected, taken down, and their place supplied with 

 others of hot water, merely in consideration of the consumption 

 of fuel and extra attention required by a steam apparatus, keep- 

 ing the danger of explosion out of the question. 



It seldom happens that the pipes of a hot-water apparatus can 

 be raised to so high a temperature as 212 ; in fact, it is not 

 desirable to do so, because it is unnecessary to generate steam, 

 which would only escape by the air vent, without affording any 

 available heat. Steam pipes, on the contrary, must always be 

 above the temperature of 212, otherwise steam will not be gen- 

 erated ; and here the grand point to be attended to in artificial 



