Year: 1870

Two kinds Of experiment are now and
have been for some time in progress, having
for their common object the Improvement Of
steam boilers These experiments are con
Quoted by two sets of inventors, and have
each done much to educuate the steam con-
suming public. The FIRST has for its aim
the increase Of the factor Of safety to its
highest point the other aims at the increase
of economy in the production of steam.


1t is, perhaps. little singular that those
who aim at greatest safety, as well as those
who aim at maximum economy, should have
for the most part adopted tubular construc-
ton, with the distinction that the greater
economy part use the tubes as Hues through
which to transmit the gases Of combustion,
and thus enlarge the heating surface while
I<hs safes1 S.ssky p 4ssaese eisso The suaEz,
and apply the hsAt outside. thereby secur-
ing great heating surface. while accumulated
system, though safe, is uneconomical.
Notwithstanding this, the number of
boilers constructed so as to make safety the
principal point secured, are multiplying in
the market, and are finding ready sale in
many instances. There is without doubt a
mean between these extremes, mean that
gives both maximum economy with maxi
mum safety, so far as these can be stimuli
taneously attained. and we believe we have
seen boilers in which this mean is attained !;
but il is not our purpose to commend any
particular boiler, however much it might
serve us in illustrating our views upon this
subject.


Most of these boilers in which the attain
ment Of maximum safety is made the para
mount object, are subject to the great defect
of foaming, or priming, as It is called, 50
that the amount of water passed through
them by the action Of beat is no index Of
their true evaporative power. And as the
economy Of a boiler is entirely dependant
upon its evaporative power, or the amount
of water it can truly convert into steam
per given weight Of coal consumed, it may
well be doubted whether the factor of safety
is not too dearly purchased in this class Of
boilers.


Some recent experiments, to which we
may refer more particularly at future
timer seem to show that in their ordinary
mode of estimating the quality Of steam BY
the hand. and its appearance when discharg-
ed into the air, very great errors in judg-
ment are committed and it is probable
that many boilers claimed to evaporate from
IL to 8 lbs. Of water per ID. of coal con-
sumed, do not really do more than half that.
1t is further probable, that absolute nor
NAL steam. from working boilers is much
more rarely delivered to steam engines
than is at present supposed.


The experiments referred to have also
rendered it almost certain that the proper
ton of priming within certain limits is
exactly as the rate at which the steam is
delivered al other things being equal
and that there is limit to rapid delivery
beyond which almost any boiler will prime,
more or less no matter how well it is con-
structed; and still another limit below
which no boiler will prime, no matter what
its form may be. And further, these ex-
periments indicate that boilers deemed safe
when delivering wet steam may be unsafe
when this delivery is 50 reduced as to force
them to deliver dry steam although Of
course, no boiler composed Of small pipes,
their equivalent, can produce such havoc by
explosion, as one in which the water and
steam are massed, and disruptive pressure
accumulated upon an outside shell.