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ciety, discusses the principles of them so well, 
that we cannot do better than copy a consider- 
able portion of his paper. “ Experience,” says 
he, “led to enquiry as to the best means of con- 
structing large tanks; and here it appeared, in 
the first place, that failures had occurred in con- 
sequence of projectors of tanks having adopted 
methods that promised great economy in the 
construction, but which eventually proved fail- 
ures. In some cases the defects had arisen from 
the tank being incapable of retaining the liquid 
collected therein, while, in others, it arose from 
an opposite cause—the incapacity of preventing 
the circumjacent water from entering the tank 
and too much diluting the manure; hence, in 
place of an economical result, such tanks were 
rendered useless, unless a double expense was in- 
curred to reconstruct them. It appeared also 
that some of those failures had been, in some 
measure, the result of neglecting, on the part of 
the constructor, the laws of hydrostatics. Thus, 
in the case of tanks being formed like wells— 
that is, their depth being considerable—in which 
case the counteraction necessary to resist the 
hydrostatic pressure becomes greatly more diffi- 
cult, whether from the liquid within or from the 
circumjacent water pressing from without. For 
this reason alone it became a fixed point, in the 
views of the writer, that, in all cases, there is 
safety in avoiding the construction of deep wells 
to serve as tanks.—Still further consideration of 
the subject led to the inquiry as to the best form 
of a tank, and this was found to involve another 
question—the nature of the ground and substrata 
in which the tank is to be formed. It is, in the 
first place, evident, from the case of well-tanks 
already stated, and from due consideration of the 
effects of hydrostatic pressure, that the diffi- 
culties and even the expense of construction, 
especially as regards tightness, will always be 
diminished in proportion to the decrease in depth 
of the tank; and in no case should the depth ex- 
ceed eight or nine feet. In most cases it will be 
advisable to limit this to six or seven feet, or 
even less, where the ground may be unfavourable. 
It being essential also that tanks should be close- 
ly covered, both for safety and preserving the 
ammonia, it follows that arching with stone or 
brick, as being more durable than timber, should 
in all cases be resorted to; but since arching 
becomes more expensive as the extent of the span 
increases, it becomes necessary again, with a view 
to economy, that the width of the tank be limited 
to six or eight feet, and from this it follows that 
capacity must be always obtained, principally by 
extending the length; or, when circumstances 
require that.a tank must be limited in its length, 
| capacity may be obtained by extending the width 
to two or even three times the limit here pre- 
scribed, and then subdividing it into three cham- 
bers or vaults, by division walls, in which requi- 
site openings are formed to give the effect of one 
reservoir. Upon these and the boundary walls, 
TANK. 
two or three arches, as the case may be, are to 
be thrown, covering in the whole area. This 
last form of tank, while it may appear more ex- 
pensive, will, in fact, be rather less so than the 
single one. 
“The actual construction of tanks will always 
be, in some degree, modified by the strata in 
which they are placed, and, from the different 
nature of the strata, may be divided into three | 
kinds, viz., clay, rock, and gravel, but in each of 
these there will be varieties. Tanks formed on 
the first kind of strata, especially on the moun- 
tain or boulder clay, will be done with little 
difficulty, such clay being generally highly im- 
pervious, and will require only the requisite ex- 
cavation, and lining the same with walls of rubble 
masonry to carry the arched covering. In the 
alluvial clays, in which pervious strata sometimes 
occur, it may be necessary to treat the con- 
struction in the same manner as will be required 
in the more pervious gravels and rocks, that is, — 
by careful puddling ; but there are many localities 
where this variety of clay is quite impervious, 
and hence nothing but excavation and building 
are necessary. In the second kind—rocks—the 
same variety of circumstances may occur; they 
may be perfectly dry, or they may contain springs 
of water. In the first case nothing more is ne- 
cessary than to excavate and build; but, in the 
second, every precaution is required, both to pre- 
vent entrance of spring water and the escape of 
the manure. To puddle only, in such a situation, 
would be endless; for, whenever the tank might 
be emptied of the manure, the circumjacent 
water would press upward against the bottom 
puddle, which, if not pervious, would be broken 
up, and so admit water, and in either case the 
destruction of the tank must follow. To secure 
a tank in such a position, the certain method is 
to carry a drain from the lowest point of the 
excavation to the nearest outlet—this being done, 
all danger of pressure from without is removed, 
and the tank may be completed with a layer of 
puddle all over the bottom and sides, upon and 
against which the rubble walls are built, with 
the certainty of a successful result. In the class 
of gravels, artificial drainage will seldom if ever 
be required, there being seldom any danger of 
hydrostatic pressure from circumjacent water— 
the construction of a tank here will therefore 
proceed, as last described, by puddling and 
building. But, should it so happen that water 
is found to stand in the excavation, then draining 
must be resorted to; for it is incompatible with 
the nature of such a structure that it can both 
hold in and hold out water; for, though the 
sides might stand, the bottom would ultimately 
be forced upward, unless recourse is had to the 
expensive alternative of an inverted arch of stone 
or brick, laid over the bottom puddle. Localities 
may indeed occur where such an expedient might 
be advisable, but such a case must be the ex- 
ception and not the rule. In the construction 
a 
