=e 
TANNIC ACID. 
of tanks it should be kept steadily in view, that 
where puddling is required it becomes the es- 
sential means of rendering the work perfect ; 
and, therefore, the greatest care should be be- 
stowed upon it. The kind of puddling required 
for the purpose is what may be named dry pud- 
dle. It is well tempered pure clay brought to 
| such a firm consistence as will just allow of any 
two pieces, on being pressed together, to unite 
into a solid mass. It is made up into irregular 
balls or lumps and thrown with force into its 
place. A succession of such balls are laid all over 
the bottom of the excavation to the depth of at 
least one foot, they are thrown down, pressed, 
and beaten firmly together till the whole forms 
one solid mass. When the stratum of bottom 
puddle has been sufficiently consolidated, the 
side walls are founded upon the puddle with 
broad flat stones. The bottom puddle must ex- 
tend to at least one foot in breadth beyond the 
foundation of the walls, and upon this extension 
the wall puddle is founded, being first well in- 
corporated with that of the bottom, and after- 
wards carried up regularly with the stone walls. 
The walls and arch may be built in rubble ma- 
sonry as already stated, or of brick-work. To- 
wards each end of the arch a hatchway or man- 
hole should be formed, for the purpose of gaining 
access to the tank, and for ventilation when re- 
quired ; but these are usually closed with a cover, 
and a third opening is required for the pump. 
The floor of a tank, puddled as here described, 
must be paved with rough flagstones regularly 
jointed, or with brick laid on edge, to prevent 
the waste of the puddle. It is necessary also 
that the floor have a small declivity towards the 
point where the pump is to stand. There remains 
to be noticed that, in choosing a site for a tank, 
it should be so placed that the surface of the li- 
quid in the tank, when full, shall be sufficiently 
below the level of all the sources of supply, as to 
give a free current from them through the drains 
or conduits to the tank. It is advisable also that 
the conduits should be water-tight, for which 
purpose burnt-clay pipes, of three to four inches 
_ bore, properly jointed, are the most eligible; and, 
to prevent choking of the conduits, their eyes 
should be defended by a grating, besides having 
a water-trap or cess-pool immediately under it, 
to intercept any grosser substances that might 
enter, and which in time tend to close up the 
conduits. It is also worthy of notice that, on 
some farms, the position of the steading, if on 
sloping ground, may allow of the tank being so 
| placed. as to admit of its contents being drawn 
off by a pipe and stop-cock, and thus delivered 
| into the manure-cart without the intervention 
See the articles Lrqurp Manus | 
of a pump.” 
and Liguip Manure Carr. 
TANNER’S- BARK. See Tan, Bark, and 
TANNIN. 
TANN IC ACID. The peculiar vegetable prin- 
ciple which combines with the gelatine of skins 
mm 
TANNIN. 399 
and converts them into leather. See the article 
LeatuEr. It can be separated from the vegetable 
substances which most abundantly contain it, 
and especially from gall-nuts, by any one of seve- 
ral chemical processes; and, when separated and 
purified and dried, it is a white, odourless, fiercely 
astringent, uncrystallizable powder, very soluble 
in water and alcohol. A solution of it reddens 
litmus paper; and, when exposed to the air, be- 
comes yellow, yellowish-brown, and dark-brown ; 
and when evaporated to the consistence of an 
extract, is rendered partially insoluble. It de- 
if up in its own astringency; and is decomposed 
by nitric acid and by chlorine in a very obscure 
or complicated manner; and is precipitated by 
the carbonates of potash and ammonia, by alumi- 
na, by the alkaline earths, and by many of the 
oxides of the common metals. It forms with 
the peroxide of iron, or still better with a mixture 
of the peroxide and the protoxide, a black-col- 
oured compound which, together with gallate of 
iron, constitutes the basis of writing ink and of 
the black dyes; and it combines with gelatine in 
solution to form a yellowish flocculent precipitate 
which is insoluble in water, and powerfully resists 
putrefaction, and becomes hard and tough when 
dry. This precipitate bears the name of tanno- 
gelatine, and is the essential basis of leather, and 
is always formed and deposited within the sub- 
stance of skins when they are macerated in an 
infusion of bark. The ultimate composition of 
tannic acid, according to Berzelius, is 52°69 per 
cent. of carbon, 43°45 of oxygen, and 3°86 of 
hydrogen. 
TANNIN. Impure tannic acid. Yet the 
names tannin and tannic acid are very often 
used as strictly synonymous, by the former being 
put instead of the latter. Tannin occurs in the 
bark of most trees, in the excrescences or gall- 
nuts of several species of oak, in some inspissated 
juices, such as kino and catechu, in the leaves of 
such plants as tea, sumach, and whortleberry, 
and in general in all astringent parts of all 
astringent plants. It is in fact the chief princi- 
ple of vegetable astringency; but it varies some- 
what in character in different plants, somewhat 
in quantity at different seasons in the same plant, 
and very greatly in proportion or relative amount 
in the corresponding parts of different plants. 
For example, the tannin of some plants strikes a 
green colour with salts of iron, while that of 
most strikes a black or a bluish-black colour; 
the tannin of any tree is generally more abundant 
in the inner cortical layers of the bark than in 
other parts, and much larger in quantity at the 
budding period of spring than in any period of 
autumn and especially of winter; and the per- 
centage of tannin in a few of the principal sub- 
stances which contain it is as follows,—2°2 in 
willow bark, 2'7 in elm bark, 4 in the inner 
coloured bark of the oak, 4°3 in chestnut bark, 
| 6°3 in ordinary oak bark, 8°5 in green tea, 10 in 
stroys the acidity of acids, or completely swallows | 
