790 SODA.— Sulphate Roasters.

form of a cupola of half a brick’s thickness. In

from 12 to 18 inches in diameter; these pipes rise

the latter case it is impossible that the arch should

perpendicularly to such a height that from thence

be damaged by the boiling over in the pan without

there is a continuous fall towards the first condensing

its being noticed, and in no case is it possible that

cistern, or towards the condenser itself, if there are

any gaseous hydrochloric acid can find its way un-

no such cisterns provided. The pipes are made of

perceived into the fire flues, and thus escape reach-

very carefully-prepared fire clay and are well boiled

ing the condensers. To be sure, the arch must be

in tar; latterly they have been also made of glass.

renewed every time a new pan has to be put in; but

Lastly, there is beside each pan a gauging cistern

this can be done in a few hours’ time, during which

for the sulphuric acid. This is usually of cast

time the furnace may be heating up again. Plate

iron lined with lead, is heated from underneath

I. also shows an excellent way of arranging the

by the waste heat of the pan flue, or otherwise,

fire underneath the pan, about which there are many

and is provided with a gauge float or other means

opinions. Very much depends upon this arrange-

of accurately measuring the acid; and with a self-

ment, both for the amount of work to be got out of

acting syphon, which discharges itself into a cast-

the pan, and for the time it will last. The setting

iron pipe leading through the pan arch into its

as shown will allow of the greatest possible produc-

interior, not quite on its margin, but a little way in,

tion of salt cake by the pan, without preventing it

so that the acid runs on to the salt, not on to the

from being worked at a slower rate, if necessary.

metal, which would very soon wear away in this

Sometimes the decomposing pan is heated by the

place. These cast-iron pipes wear out very soon,

waste heat from the muffle furnace ; but this arrange-

and must be replaced from time to time.

ment is quite erroneous when anything like a large

The calcining furnace itself, as mentioned above,

and regular production is required. In a few

maybe either an “open drier” or a “close roaster.”

cases, again, the fire is carried, not only under,

An excellent form of open drier, such as used on the

but also over the decomposing pan. If divided

Tyne, is shown in the diagrams on Plate I., which

from it by an arch, it is intended to prevent a

render any further explanation almost superfluous.

condensation of hydrochloric acid, which, however,

The fire-places, the connection with the pan, the

in any case does not take place in or near the pan. If

working-doors, which likewise serve for discharging

the fire is directed over the pan itself, as is done in

(“ drawing”) the sulphate, the escape flue for the

a few cases by means of the flame of an adjoining

gas, &c., are clearly visible. These furnaces go a

“ open drier,” it hastens the work, but dilutes the

long time without any essential repairs, provided

acid gas so much that the condensers do not yield

that they are lined with very hard, well-burned fire-

anything but weak acid. Neither arrangement is

bricks, capable of resisting the acid, which is of far

adopted in any large number of works.

greater importance in this case than mere resistance

In every case there is a working or charging hole

against heat. The whole arrangement shown on the

provided in front of the pan, generally shut during

plate (pan and drier together) represents essentially

the operations by a leaden door, with a round opening

the plans used in all Tyneside works, although of

for the handle of a rake to pass through; through

course there are differences in unimportant details

this door the salt is thrown in and the charge

in "every factory.

worked. Another opening leads out of the pan into

The “close roaster” is shown in Plate II.; the

the furnace, known as the “shoving hole” or the

arrangements of the pans and fltfes explain them-

“gangway.” This is either opposite the charging

selves. These furnaces are subject to more repairs

door, in which case the charge is pushed through by

than open driers; they must be built with extraordi-

means of a rake, and the pan then forms a continua-

nary care to begin with, since otherwise the acid

tion of the length of the furnace; this is called

gas soon finds its way through cracks in the arch

“ shoving. ” Or the second opening is placed at

and in the beds, and what is almost worse, the

right angles to the charging door; the pan is then

melted sulphate itself runs through any chinks in the

called a “casting” pan, and the charge is removed

bed and stops up the flues underneath. Such cracks

by means of a large shovel (“casting shovel”) with

are often only discovered after the gas has escaped

a long iron handle, worked through the charging

through them into the fire-flue for some considerable

door. In this case the pan is fixed at one side of

time; and in the opinion of the Tyneside ash makers

the furnace. Local convenience must decide which

it is far more difficult to insure a complete conden-

arrangement is to be preferred; the engravings show

sation of the muriatic acid when using close roasters

the former. In any case the shoving hole is pro-

than with open driers, where such escapes are im-

vided with a cast-iron damper, which is only lifted

possible, as the acid gas goes into the condensers at

during the time of shoving or casting; and as these

the same time with the fire gas. The great advantage

dampers are soon acted upon by the acid and do

of close roasters is the greater concentration of the

not then shut tight, it is a great improvement to

acid gas, which certainly not only allows it to be

use a double damper — one modification of which

condensed more easily, that is, with smaller con-

is shown in Plate I.—the space between the

densers, but also to make more highly concentrated

dampers being filled with salt. Salt is also heaped

muriatic acid from them; and formerly it was

round the top of the damper, and in front of the

assumed that this would insure a more complete

working door, to keep the gas in. Each pan has

condensation than with open roasters, but the

further an exit pipe for the hydrochloric acid gas,

above-mentioned difficulty of keeping the real muffle

J