40 



HOT TVATER APPARATUS. 



the bars both in length and breadth, and the coals which are placed on 

 this blank part of the furnace, in consequence of recei^ing no air from 

 below, -will burn very slowly, and will only enter into complete combustion 

 when the coal which hes directly on the bars have burned away." 



It has been laid down as an invariable rule by a very competent judge, 

 that no pipes should be used for this purpose of a greater diameter than 

 four inches, nor less than three inches, unless in the case of pits or any 

 small houses, when a very moderate temperature is to be kept up; in such 

 a case, pipes of less diameter may be used. Larger pipes will of course, 

 when once heated, continue to give out their heat longer than small ones, 

 after the fire is extinguished, but they require an equal length of time 

 and consumption of fuel to heat them. Besides, the friction is much 

 greater in small pipes than in large ones, arising from the circumstance of 

 the increased surface with which a given quantity of water comes in contact 

 when passing through a smaU pipe, and also the greater velocit}- with 

 which the circulation goes on. 



Pipes should be of a uniform size throughout their whole length, unless 

 circumstances occur subjecting that rule to deviation ; this will some- 

 times occur when two or more departments are to be heated from the same 

 boiler, and these are at a distance from each other. In such cases, the 

 pipe, which is merely intended to connect the more distant parts, may be 

 smaller in diameter, as for example, if a boiler were to be placed equi- 

 distant from four pits, a smaller pipe might be laid under ground, or 

 otherwise, to convey the water to the pipe within the pit, which latter 

 is to give off heat ; the smaller pipe from the increased velocity of the 

 water passing through it, would loose but httle of its heat during its 

 passage. All alterations in the size of pipes, either by enlai'ging or con- 

 tracting theu' diameter, effects the velocity of the circulation in a greater 

 or less degi'ee. Yentmi, discovered that the velocity of a given quantity 

 of water would be effected by enlargements in the pipes to the following 

 extent. 



A straight pipe in 109 " 



A pipe T^-ith one enlai'gement required 147" 

 „ three „ ,, „ . 192'' 

 „ five „ „ „ 240" 



In regard to the quantity of pipe required to heat hot houses, ^Ir. 

 Hood has laid down the following scale : — For greenhouses, conserva- 

 tories, and such like buildings where the temperatm*e is required to 



