106 ON THK MERITS OF IRON AND WOOD FOR ROOFS 



an inch to two inches in* diameter, for in the first place on no 

 account should dirty water be used, as it causes a settlement or 

 accumulation of mud, which in time not only 'injures the boiler, 

 but lessens its power, by not only preventing the fire from acting 

 immediately on the water, but also because the accumulated de- 

 posit impedes the circulation of the fluid by diminishing the 

 calibre of the water way, and ultimately forms a hard incrustation 

 similar to what is seen on the bottom of steam boilers, and it fre- 

 quently ends by burning a hole in the bottom or other parts of 

 the boiler. 



Some times in order to save a little trouble, where hard water 

 is more conveniently obtained than soft or rain water, the boiler 

 is filled with hard water which is as injurious as mud, for in the 

 decomposition of the water, consequent on the process of boil- 

 ing, earthy particles are] deposited , at the bottom, but if rain 

 water is used, all this injury is prevented: as, I have-on several 

 occasions examined boilers that had been taken down after being 

 in use for ten or more years, and where this important part had 

 been properly attended to, there has scarcely been an appearance 

 of incrustation. Moreover, in all plans of boilers, there should 

 be a small cock so placed as to draw the whole of the water off 

 occasionally, for the purpose of cleaning the boiler, &c, as it is 

 well known that water when heated, "not only evolves or gives out 

 its component gases, but by mechanical deposition any matter, 

 held in solution in the water, falls to the bottom, and this causes a 

 sediment on the boiler, but by the use of rain or if convenient, 

 filtered water, all this difficulty is overcome. 



There is also another difficulty attending hot water, which if 

 properly attended to in the first place, would not be such a per- 

 petual source of inconvenience, namely, when water has to de- 

 scend under door ways, &c, or to dip below the bottom of the 

 boiler; I have frequently known in small plans of hot water which 

 are admitted to be good in themselves, prove of no service in the 

 cases described ; nay, it has even been found necessary to remove 

 them in consequence of the water not circulating under the paths, 

 and other situations when it was necessary to descend and rise 

 again, all this might have been avoided by giving the flow pipes a 

 proper ascension when leaving the boiler, and by placing the re- 

 servoir, or cistern sufficiently high so as to counteract the power 

 of the water in the return pipes: I was sent for last spring to 

 remove an apparatus in a lady*s greenhouse at Westerham, in 



