Notices respecting New Books. 295 
reverberatory furnaces, at page 302 of this volume :—“ In rever- 
beratory furnaces for the decomposition of neutral salts and the 
manufacture of alkalies, ash-pit-doors are of no use, as it is never 
necessary to check the fire suddenly, as in other operations. On 
the contrary, [ have found it advantageous to have the ash-pits 
as deep, and the chimneys as high, as possible, in order to occa- 
sion a strong and uninterrupted draught. I cannot suffer this 
opportunity to pass without remarking, that the proprietors of 
reverberatory furnaces should contrive to continue their processes 
night and day; or, if that be impracticable, they should rake up 
the fire and stop the passage to the chimney so as to prevent the 
furnace from cooling during the night. Furnaces thus worked 
will last six or seven times as long as those do which frequently 
stand idle. The contraction of the materials during the time of 
cooling, and the subsequent expansion, wear them out rapidly.” 
But in our estimation the most important part of this essay is 
that where the author urges the necessity of attending to fempe- 
vature in the conduct of manufacturing processes. A great num- 
ber of cases in corroboration of this advice are adduced, which 
are well deserving of the perusal of all practical men: see page 
341—382. The detail of the facts above alluded to is concluded 
in the following manner :—* I trust enough has now been offered 
to induce every manufacturer who may peruse these loose hints, 
to apply them to his own business, and to consider whether some 
of his own peculiar processes might not be very materially im- 
proved by a variation of the temperature at which they have 
usually been conducted. This is the chief object I had in view 
in composing this essay; and as all the principal observations are 
founded upon experience and the best information | could procure, 
I entertain some confidence that it will be acceptable, and prove 
highly useful—especially to the British manufacturer.” 
“© The superior knowledge of our manufacturers has been the 
great source of our excellence as a commercial nation ; but there 
is a danger, amid the growing intelligence of the age, of our losing 
this proud pre-eminence, unless some spirited individuals, in every 
elass of society, aim at informing the public mind, and exciting 
that emulation among our respective artists, which is sure to 
stimulate their exertions and lead them on to perfection.”’ ‘These 
remarks are closed by some spirited national observations, which 
will be read with considerable interest. 
The third essay in these volumes is entitled SpeciFic GRAVITY; 
aud as we do not recollect ever to have seen any treatise express- 
ly on this subject, we deem it as important as any which the work 
contains. It is well calculated to instruct young people in all the 
different modes of ascertaining the specific gravity of gasses, fluids 
and solids. It contains some original tables for the calculation of 
T 4 specifie 
