32 Transactions. — Miscellaneous. 
under double the pressure of a cold blast. From the increased diffusibility of 
these gases, it follows that the boiler tubes can be reduced in diameter, and 
consequently made thinner with safety ; and, as combustion is rendered 
complete, there will be no smoke to deposit soot in them. 
The advantage to be derived from the use of a hot, in place of a cold, blast 
. is clearly proved in a series of blow-pipe experiments made at the laboratory 
of the Geological Survey of New Zealand, and published in Vol. II. of the 
“Transactions,” where it is shown that such refractory substances as platinum, 
fire-clay, flint, pipe-clay, agate, and opal, were fusible if air at a temperature 
of 500° F. be employed. And with an exalted intensity of heat in the 
furnace, we are enabled to avail ourselves to a still greater extent of the 
economy arising from both the super-heating of the steam and its subsequent 
expansion in the cylinders of the steam engine. 
DESCRIPTION OF PLATE. 
A The air tube, the top of which supplies the blower Е. 
B The tube containing the gases of combustion. 
C Ash pan, containing water. 
D A door which can drop and close the tube В. 
G A tube, or space, the full width of the thermo-convector, through which the waste 
and cooled gases can be discharged upwards to the funnel. 
E The blowing apparatus supplied with the fresh heated air from the top of the 
tube A, by means of a space similar to G, and which fills in the front of the convector, 
but is removed in the figure in order that the interior can be seen. 
H Reservoir of hot air. 
J Water space of boiler perforated by the air tubes. 
K Fire doors, enclosing space holding a charge of fuel. 
Авт. V.—On the most Economic Mode of Felting Steam Boilers. 
By J. C. Fiera. 
(PL V. бов. 1 and 2.) 
[Read before the Auckland Institute, 6th October, 1873.] 
During the period when low-pressure condensing steam engines were in 
general use, various plans were adopted to prevent waste of steam and heat in 
boilers by condensation or radiation. With boilers at 1UIbs. to 15168. pressure, 
a simple covering of felt, protected by wood or canvas, answered sufficiently 
wel. But when steam boilers are run, as at present, at bOlbs. 751s., 
or 1001s. per inch, for working steam expansively, or for working 
compound engines, it has become much more important that the surface of а 
LJ 
