FinTH.—On Felting Steam Boilers. 33 
boiler working at these high pressures should be so protected that heat and 
steam may not be wasted by radiation or condensation. 
lt is true that common felt cased with bricks will prevent much conden- 
sation and radiation, but with the serious disadvantage that a leakage from a 
rivet, or otherwise, causes rapid corrosion when running unobserved under the 
brick casing, and with the further disadvantage that the felt is destroyed in a 
very short time. 
Various materials, such as asbestos, cloth, or fabrics saturated with 
chemical preparations, have been tried, but, so far as my investigations have 
gone, much the best material yet discovered is common felt. 
The proper application of felt has been, and I believe still is, the real 
difficulty. Applied in contact with the surface of a steam boiler at even 
50lbs. pressure, felt will need replacing about once in six months, About 
two years ago, to lessen this destruction of felt, I made a species of hurdles or 
gridirons of common hoop-iron, with wooden battens of 1 in. thick rivetted to 
the hoop-iron. These were placed upon the boiler, and the sheets of felt laid 
upon them, the upper surface of the felt being protected by canvas. This 
plan secured a small space between the boiler and the felt, but, though a great 
improvement upon the old plan, I found that in the course of about fifteen 
months the wooden battens had become charred and the felt a stratum of dust, 
slightly adhering, indeed, to the canvas back if undisturbed, but practically 
useless. Both substances had simply been destroyed, as before, by too close a 
contact with the boiler. 
A very simple contrivance now presented itself to my mind, which I 
immediately put in operation. I constructed an iron grid as before, but with 
one important difference. I placed pieces of hoop-iron aa (Figs. 1 and 2) at 
10in. distance, to lay on the circumference of the exposed portion of the 
boiler. I then prepared transverse pieces of hoop-iron BBB (Figs. 1 and 2), 
putting two double cranks in each cc (Fig. 1) 2}in. highx21in. wide. 
I placed these transverse pieces at 10 in. distance, and rivetted each of the 
cranks at D (Fig. 1) to the pieces of hoop-iron intended to lay on the circum- 
ference of the boiler. When cranked, the transverse pieces were 21 in. long, 
about the width of an ordinary sheet of felt. Upon these cranked pieces I 
placed wooden battens 2 in. broad by 1} in. thick ЕЕ (Figs. 1 and 2), screwing 
them together at rrr (Fig. 1). This completed the hurdle, or grid, 21 in. 
wide, and of sufficient length to lay across the boiler from side to side. 
I next provided sheets of felt long enough to cover each grid, sewing each 
sheet to strong canvas 24 in. wide, thus leaving at one side a margin of canvas 
to lay over the sheet of felt on the adjoining grid. The 4 in. air space (which 
may be increased at pleasure by increasing size of cranks) between the boiler 
and felt, besides preventing all charring of wood or felt, is an excellent 
E 
