432
MANUFACTURES.
Manufac- serves to let out the steam, but will not admit any con-tures. densed water to enter. The steam raised in the lower— > boiler rushes through this opening in the iron partition,and acts upon the upper boiler so as to heat it and eva-porate it to a certain degree, and this steam being con-densed falls down upon the cover of the sloping coverof the lower boiler, and runs off through the waste pipese to the drain, as shown in the figure.
The waste water being warm, imparts heat to thebrine as it is conducted along the pipe p, which is thepipe of a force-pump for forcing the raw brine from thebrine well to the upper boiler, and which is laid along thewaste drain f for this purpose : n n are rakes with ironhandles working through air-tight stuffing-boxes b;these are for the pupose of raking the salt to the forepart of the boiler where it is taken out at the manhole m.
The lower boiler must be provided with a safety
valve in the usual way. Alderson on. the Steam, En- Mechanical
gine Processes.
The following Table shows the result of a course ofexperiments to determine the amount of impurities in Dr.Henry®different descriptions of salt, by Dr. Henry, and published anal 7 sis 'by him in the Philosophical Transactions for 1810.
These experiments were undertaken principally with aview of ascertaining the comparative qualities of differentforeign and British salts.
From an examination of the results in the last twocolumns, the total amount of impurities, and the quan-tity of muriate of soda contained in each variety of com-mon salt, may be immediately seen; and from these itappears that the Toreign bay salt is purer, generallyspeaking, than salt which is prepared by the rapid eva-poration of sea water, but that it is contaminated morethan twice as much as the stoned and common salt ofthe Cheshire district.
r St. Ube’s.
< St. Martin’s.
lOleron ..
(■Scotch (common) ,
from < ® cotc ^ (Sunday).
saltsea water.
1000 parts of which consisting of
Inso-
luble
matter.
Muriateof lime.
Muriateof mag-nesia.
Total
earthy
muri-
ates.
Sulphateof lime.
Sulphateof mag-nesia.
Total
sul-
phates.
Total
impuri-
ties.
Puremuriateof soda.
9
a trace
3
3
23*
4*
28
40
960
12
do.
3*
3*
19
6
25
40*
959*
10
do.
2
2
m
4*
23|
354
9641
4
28
28
15
17*
32*
64*
935*
1
.,
H*
1U
12
4*
16*
29
971
2
,,
11
11
15
35
50
63
937
1
5
5
1
5
6
12
988
10
_3_
i
6L
. .
6*
16f
9831
1
i
3
1
Hi
. .
Hi
131
986f
1
i
f
1
14A
. .
14*
16*
983*
1
4
1
■4
1
15*
15*
17*
982*
Salt duty.
(618.) Table showing the Amount of the Salt Duty perAnnum from 1820 to 1825, when the Duty was re-pealed.
Amount.
£1,529,862
1,553,841
1,490,007
385,325
220,098
8,895
Years.
Duty
per Bushel.
1820
15s.
1821
15
1822
15
1823
2
1824
2
1825
2
1826 Duty repealed.
(619.) Epsom Salts , or sulphate of magnesia, wouldhardly have been thought of sufficient general interest asa British product to be introduced in this place; but it isso intimately connected with the preceding article, that afew lines descriptive of the process of its manufacturewill not, we trust, be considered misplaced. In orderto illustrate this, it will be necessary to describe a littlemore particularly than we have done, the process fol-lowed at Lymington , in Hampshire , in the formation ofcommon salt. As the climate there is warmer than inmost other parts of our coast, advantage is taken ofthis circumstance to concentrate the sea water by spon-taneous evaporation to about one-sixth of its bulk,before admitting it into the boilers; and one differencein the subsequent process is, that the salt is not therefished out of the boilers and drained, as we have before
described, but the water is entirely evaporated, as by thepatent apparatus, and taken out once every eight hoursand removed into troughs having holes in their bottoms.Through these it drains into pits made under ground,which receive the liquor called bittern or bitter liquor.Under the troughs, and in a line with the holes, arefixed upright stakes, on which a portion of salt, thatwould otherwise have escaped, crystallizes, and forms, inthe course of ten or twelve days, on each stake, a massof sixty or eighty pounds. These lumps are calledsalt cats. They bear the proportion to the common saltmade from the same brine of one ton to one hundred.
From the mother-brine or bitter liquor, which hasdrained into pits, the sulphate of magnesia is madeduring the winter season, when the manufacture of saltis suspended, in consequent of the want of the tempera-ture required for the spontaneous evaporation of thesea water. The process is a very simple one. Thebitter liquor from the pits is boiled for some hours in thepans which are used in summer to prepare commonsalt, and the impurities, which rise to the surface, areremoved by skimming. During the evaporation, a por-tion of common salt separates; and this, as it is too im-pure for use, is reserved for the purpose of concentrat-ing the brine in summer. The evaporated bitterliquor is then removed into wooden coolers, eight feetlong, five feet wide, and one foot deep. In these itremains twenty-four hours, during which time, it the