106 



top of the tank is covered with large slabs of slate, 

 cemented together, to prevent the excessive escape of 

 steam. Around this is a frame sufficiently high to 

 retain the hark, in which the pots are plunged. The 

 boiler and tank are filled with water, and this circu- 

 lates, when the fire is lighted under the former, by 

 means of two pipes, one from the top of the boiler, 

 and the other returning nearer to its bottom. The 

 expense of piping, and danger of its freezing, is 

 avoided ; the fire only requires to be kept lighted for 

 two hours at night, and again for the same period in 

 the morning ; the water, when once heated, retaining 

 its temperature for a long time. In a small house the 

 apparatus can be constructed for £5 ; and in all, for 

 less than half the cost of hot water pipes. The 

 saving in tan and labour is also very great ; in some 

 places tan costs 19s. per cart load, and where it is 

 cheaper, the trouble and litter incident to its employ- 

 ment, and the dangers of loss from fungi and insects, 

 of which it is the peculiarly fertile foster-parent, ren- 

 der it objectionable as a source of heat. And when- 

 ever the tan has to be renewed, the trouble and de- 

 struction of plants is always great. 



" In the following sketch, for which we are in- 

 debted to Mr. Eendle — A is a transverse section of 

 Roger's conical boiler; B is the fireplace; g, the 

 tank ; c, the flow-pipe ; d, the pipe by which the 

 water returns to the boiler ; e, is the hole for the 



