158 Report on the Geological Survey of Connecticut. 
About 900 tons of ore go annually from the Salisbury beds to the 
Ancram iron works, and 800 tons of the Kent ore are consumed near 
the ore bed. 
The annual produce of cast iron from the hematite of the aes 
may therefore be estimated at 4500 tons. 
Mr. Shepard has the following valuable remarks and citations on 
the subject of the manufacture of iron. 
‘Tn the fabrication of cast-iron it must be obvious, that a certain 
temperature is necessary to secure the favorable working of the fur- 
nace. If this is not reached, all the stock added, is (in the language 
of the furnace-men) “cut to pieces”’ without any reduction of the 
metal. ‘The manner in which the hot-blast secures the heat required, 
is at once understood if we reflect upon the ascertained fact, that in 
a furnace whose charges of stock amount to two tons per hour, the 
weight of air driven in, is six tons for the same time. . The differ- 
ence between the admission of this prodigious weight of air at 50° 
and 600° is most apparent, especially when it is considered that it 
enters the hottest part of the furnace. In both cases, the effect it 
produces to support combustion is the same; in the latter, however, 
it does not rob the combustion of the heat it produces. But before 
quoting the verification of the rationale given, and which experience 
has furnished, it is proper to allude to the method by which the air 
is heated, and to state how it is forced into the furnace. A number 
of arrangements have been adopted in Scotland for heating the air, 
but no one in particular seems hitherto to have proved itself superior 
to the rest. In general, the method may be described to consist, in 
“maintaining at a red heat, the cast-iron tubes through which the air 
from the blowing apparatus to the furnace is conveyed. But as the 
temperature of the furnace near the nozzles becomes so much ele- 
vated, it is necessary in order to prevent the melting of the cast-iron 
lining to employ the water-tweer ; which consists of an iron lining, 
cast hollow instead of solid, so as to contain water within, which is 
admitted by means of one pipe, and allowed to escape by another 
as it becomes heated. It thus becomes practicable to lute up the 
space between the blowpipe nozzle and the tweers, whereby all loss 
of air is prevented, and the bellowing noise formerly juice ee com- 
pletely suppressed. 
“To exhibit in a satisfactory point of view the operation of this . 
arrangement, the results obtained at the Clyde iron-works, in Scot- 
land, may be instanced. 
