IRON AND WOOD ROOFS FOR STOVES, &c. 
63 
little trouble, when 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 boiling, considerable 
quantities of 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 when this impor- 
tant particular had been properly attended to, there has scarcely been any 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 causes a sediment on the boiler ; by the 
use of rain, or, if convenient, filtered water, all this difficulty is overcome. There is 
also another difficulty attending the use of hot water, which, if properly attended to 
in the first place, would not be such a perpetual inconvenience, viz., when water 
has to descend under doorways, &c, or to dip below the bottom of the boiler, I have 
frequently known several 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 where it was necessary to descend and rise 
again : all this might have been avoided by giving the flow-pipe a proper 
ascension when leaving the boiler, and by placing the reservoir 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 Kent, which could never be made to act under the door, and I suc- 
ceeded, very much to the lady's satisfaction, in causing the water to descend in 
both flow and return pipes to more than two feet below the level of the bottom of 
the boiler, after which it had to rise again to above the level of the top of the 
boiler. The lady's name I have permission and authority to communicate to any 
person wishing to inspect the apparatus, and being so perfectly satisfied with its 
working now, she has kindly offered to answer any inquiries. In concluding these 
few practical instructions or observations on the relative properties of common 
flues, steam, and hot water, I shall merely state that during my practice I have 
always considered hot water a much more congenial heat for plants and 
all other organised bodies, whether belonging to the vegetable or animal kingdoms, 
from their close analogy, and the circumstance of its containing less of the noxious 
gases, which escape not only from the surface of the flue but from all the fissures, 
however well the flues may be built, for it is impossible to confine this light and 
subtle fluid. Again, as the temperature of hot- water pipes is more equal than 
a flue at both extremities, and rarely exceeds 200° of heat, there is not that 
exhaustion of the aqueous or humid gases, which are so essentially necessary to the 
very existence, much more to the health and fruitfulness of all plants, whether 
