6’SO 
S L U 
S M E 
SMI 
stone, earth, &c. serving to retain and rais$ 
the wafer ot ilie sea, a river, &c. and on oc- 
casion to let it pass ; such is the sluice of a 
mill, which stops and collects the water of a 
rivulet, &e. in order to discharge it at length, 
nn greater plenty, upon the mill-wheel ; such 
also are those used in chains,- to discharge 
water oft lands; and such are the sluices of 
! landers, &c which serve to prevent the wa- 
ters of the sea overflowing the lower lands, 
except when there is occasion to drown, 
them. See Canal. ■ 
Construction of sluices. The construction 
of sluices ought to be conducted by an able 
engineer, who is well acquainted with the 
action ot fluids in general; and particularly 
with the situation of the place, the nature of 
the soil, &c. where the sluice is to be erect- 
ed ; if on the sea-shore, he ought to be per- 
fectly well acquainted with the effects of the 
sea on that coast, and the seasons when it is 
• calm or stormy, that he may be able to pre- 
vent the fatal accidents thence arising ; and 
it in a river, it is necessary to know whether 
it usually overflows its banks, and at what sea- 
' sons ot the year its waters are highest and 
lowest. The machines for driving the piles 
should be placed about forty yards from the 
side ot the sluice, above and below it. As to 
the depth ot sluices, it must be regulated by 
•the uses for which they are designed; thus, 
it a sluice is to be erected at the entrance of 
a base'll for shipping, its depth must corre- 
spond with tiie draught of water of the lar- 
gest ship that may, at any time, have occasion 
to enter by it. The rule usually observed, 
is to make the surface of the bottom of the 
canal on a level with the low-water mark ; 
but if the bottom ol the harbpur or canal is 
such as to be capable ot becoming deeper 
by the action of the water, Belidor very justly 
observes, that the bottom of the sluice-work 
should be made deeper than either. 
When a sluice is to be placed at the bottom 
of a harbour, in order to" wash away the tilth 
ihat may gather in it, by means of the waters 
of a river or canal ; in this case the bottom of 
the sluice- work should be two feet or eigh- 
teen inches higher than the bottom of the 
harbour, that the water may run with the 
greater violence. 
An engineer ought always to have in his 
view, that the faults committed in the con- 
struction of sluices are almost always ir- 
reparable. We shall therefore lay down 
some rules, from Belidor, for avoiding any 
oversights of this kind: 1. In order to ad- 
just the level of the sluice-work with tiie ut- 
most exactness, the engineer ought to deter- 
mine how much deeper it must be than a 
fixed point ; and this he should mark down 
in his draught, in the most precise terms 
possible. 2. When the proper depth is set- 
tled. the foundation is next to be examined ; 
ana here the engineer cannot be too cauti- 
ous, lest the apparent goodness of the soil 
deceive him ; if the foundation is judged bad, 
or insufficient to bear the superstructure, it 
must be secured by driving piles, or a grate- 
work of carpentry. 3. There should be en- 
gines enough provided for draining the water; 
and these should be entirely under the di- 
rection of the engineer, who is to take care 
that they are so placed as not to be an ob- 
stacle to the work ; and also cause proper 
trenches to be cut, to convey the water clear 
•if from the foundation. 4. When the sluice 
is to be built in a place where the workmen 
will be unavoidably incommoded by the wa- 
ters of the sea, &c. all the stones for the ma- 
son-work, as well as the timbers for- that of 
carpentry, should be prepared bdorenafid ; 
so that when a proper season offers for be- 
ginning the work, there remains nothing to 
be done, but to lix-every thing in its place. 
Sluices are made different ways, according 
to the uses they are intended for ; when they 
serve for navigation, they are shut with two 
gates, presenting an angle towards the stream ; 
but when made near the sea, there are two 
pair of gates, one to keep the water out, and 
the other to keep it in, as occasion requires ; 
the pair of gates next the sea present an 
angle that way, and the other pair the con- 
trary way ; the space inclosed by these gates 
is called a chamber. 
When sluices are designed to detain the 
water in some parts of the ditch of a fortress, 
they are made with shutters to slide up and 
down in grooves; and when they are made 
to cause an inundation, they are then shut 
by means of square timbers let down into 
cullises, so as to iie close and firm. 
SMALT, a kind of glass of a dark-blue 
colour, which, when- levigated, appears of 
a most beautiful colour ; and if it could 
be made sufficiently line, would be an 
excellent succedaneum for ultramarine, as 
not only resisting all kinds of weather, but 
even the most violent fires. It is prepared 
by melting one part of oxide of cobalt with 
two of flint-powder, and one of potass. At 
the bottoms of tiie crucibles in which the 
smalt is manufactured, we generally And a 
regulus of a whitish colour inclining to red, 
and extremely brittle. This is melted afresh, 
and when cold, separates into two parts ; that 
at the bottom is the cobaltic regulus, which 
is employed to make more of the smalt ; the 
other is bismuth. 
SMARAGDITE, in mineralogy. This 
stone was called smaragdite by M. Saussure, 
from some resemblance which it has to the 
emerald. Never crystallized. Its texture is 
foliated. Easily divided into plates. The 
laminae are inflexible. Fracture even. “Spe- 
cific gravity 3. Colour in some cases line 
green ; in others it has the grey colour and 
metallic lustre of mica ; it assumes all the 
shades of colour between these two extremes. 
According to the analysis of Vauquelin, 
it is composed of 
50.0 silica 
13.0 lime 
11.0 alumina 
7.5 oxide of chromium 
6.0 magnesia 
5.5 oxide of iron 
1.5 oxide of copper 
94.5 
SMELT. See Salmo. 
SMELTING, in metallurgy, the fusion or 
melting of the ores of metals, in order to se- 
parate the metalline part from the earthy, 
stony, and other parts. 
Smelting, or the art of fusing the ores 
after roasting, is the principal and most im- 
portant of metallurgic operations, all the 
other being preliminary or preparative to this. 
The whole attention of the miner is directed 
towards this process ; to this all his efforts 
are applied, because it affords the truly useful 
product to which his hopes are directed’ 
Though it consists in general in fusing the 
roasted ore to extract the metal, and in 
this point of view it seems to present a simple 
and uniform operation, Ur ere is, nevertheless, 
no operation which differs so much in its cir- 
cumstances, according to the nature of the 
metal and the ore required to be treated, and 
according to the furnaces made use of, the 
nature and quantity of the combustible em- 
ployed, the energy, duration, and adminis- 
tration of the fire., the addition of an appro- 
priate flux, the heat being applied in the 
midst of tiie coal or in crucibles, the pe- 
riod, the length of time, and the mode of 
casting the fused metal ; every thing, even, 
the form of the metal which flows out, varies, 
and presents to the observer very remarkable 
differences. 
When the ore is smelted, and the metal 
obtained, the whole process is not yet finish- 
ed. 1 his metal is scarcely ever pure. It is 
either altered. by certain substances foreign to 
its metallic nature; or it contains a portion of 
another metal, which alters the properties of 
this which is desired in a pure state ; or else 
it contains a portion of a metal more valu- 
able than all the rest of the mass, which it is 
necessary therefore to extract ; or, lastly, 
it is an alloy, in large proportions of several 
metals, which are required to be separated 
from each other. All the operations subse- 
quent to tiie smelting, are comprehended 
under the general name of refining, because 
the effect is always to obtain a pure metal. 
See Metallurgy. 
SMI LAX, rough bindweed ; a genus of 
plants belonging to the class of dicecia and 
order of hexandria; and in the natural sys- 
tem ranging under the 1 !th order, sarmen- 
tac a;. 1 he male calyx is hexaphyllous, and 
there is no corolla; the female calyx is also 
hexaphyllous, without any corolla ; there are 
three styles, a trilocular berry, and tw'o seeds. 
I here are 22 species; of these, the sniilax 
sarsaparilla, which affords the sarsaparilla 
root, is the most valuable. This is well de- 
scribed in the London Medical Journal by 
Dr. Wright, who, during a long' residence 
in Jamaica, made botany his peculiar study. 
“ I hi i species (says he) has stem-; of the 
thickness ot a man’s huger ; they are jointed, 
triangular, and beset with crooked spines. 
Tiie leaves are alternate, smooth and shining- 
on the upper side : on the other side are 
three nerves or costae, with sundry small 
crooked spines. 'Tiie flower is yellow, mix- 
ed with red . Tiie fruit is a black berry, con- 
taining several brown seed . 
“ Sarsaparilla delights in low moist grounds 
and near the banks ot rivers. The roots run 
superficially under the surface of the ground. 
1 he gatherers have only to loosen the soil a 
little, and to draw out the long libres with a 
wooden hook. In tins manner they proceed 
till the whole root is got out. It is then 
cleared ol the mud, dried, and made into 
bundles. 
“ I he sensible qualities of sarsaparilla are 
mucilaginous and farinaceous, with a slight 
degree ot acrimony. The latter, however, 
is so slight as not to be perceived by many ; 
and l am apt to believe that its medicinal 
powers may fairly be ascribed to its demul- 
cent and farinaceous qualities.” 
The china, or oriental species of China 
