76 OBSERVATIONS ON HEATING A PIT. 



the fir* goes out, a counter current takes place, till the water in the 

 reservoir is all cold again. 



The following particulars may prove useful to those who wish to 

 employ such apparatus. 



PROPORTIONS IN INCHES FOR BOILERS OF DIFFERENT SIZES. 



The first of these, will be sufficient for a pit containing from an hun- 

 dred to an hundred and fifty square feet of glass, the last probably suf- 

 ficient for a greenhouse of from; six hundred to eight hundred or 

 more, 'f he reservoir should contain not less than three times as much 

 as the pipes. 



The expence of the smallest boiler is about six pounds; in tin, conical 

 not curvilinear, about one pound fifteen shillings. The larger 

 boiler in copper, may be each about one pound to one pound five shil- 

 lings dearer than the other. 



The ex peace of setting, from the small size of the boiler is very 

 trifling. The best plan is a slight case, either of wood, slate, or 

 brick work, packed with saw dust, and covered from the wet. The 

 reservoir also should be similarly packed in saw dust, that no heat may 

 be wasted. 



Fig. 5. The annexed sketch exhibits the mode of arranging the 

 apparatus as applied to a pit . F. is the furnace surrounded by the 

 boiler a, the lead delivery pipe from the. top of the boiler to the cast 

 iron pipe A; BB the other cast iron pipe ; b b the return lead pipe 

 communicating with the top of the reservoir ; c the return from the 

 b ittom of the reservoir to the boiler. The boiler and reservoir are 

 outside the pit, enclosed in a small chamber of four and a half inch 

 biickwork. The lowest point of A' A viz. A' must be higher than the 



