March r, 1898.] THE TROPICAL AGRICULTURIST. 593 
bark, a system which occupied from one to two 
years before the leather was ready, has been rapidly 
giving place to tanning with liquid extracts, which 
have the great advantage of penetrating the hides 
quickly and shortening the process down to a few 
weeks. The question, therefore, is to turn to account 
the enormous quantities of bark and wood which 
at present go to pure waste in our Indian forests 
and to convert them into tannin extracts for export 
to Europe and even for use in the country. Under 
the old system of tanning, Europe had in her cold 
climate an advantage which forbade all Indian 
competition in the preparation of leather. The 
native system of sewing each hide into a bag and 
filling it with tan, besides not giving the hide enough 
time to absorb the tannin thoroughly is much too 
slow, cumbrous and space-demanding to have ever 
had any chance of producing an article fit to compete 
against the European one. But now that the use 
of liquid extracts has shortened the process of tan- 
ning so considerably, it seems absurd that India should 
export raw hides and not leather. 
Professor Henry of the Nancy Forest School has 
shown, as the result of careful and repeated analyses, 
that in the common European oak the bark contains 
most tannin, heartwood coming next, with the sap- 
wood a very bad third — so bad, indeed, that it would 
be an advantage if the sapwood could be got rid of 
by some cheap process when preparing the extract. 
The bark of the root stock is richest in tannin, the 
butt-end of the trunk being only a little behind it, 
while at the top of the trunk the bark contains 
hardly more tannin than the outer layers of heart- 
wood. As regards the heartwood, the richest portion 
is that in the butt-end ; moreover, the quantity of 
tannin diminishes from outside towards the centre 
of the tree. The heartwood of the larger branches 
contains more tannin than that of the top of the 
trunk. The very small branches and twigs, being 
nearly all bark, contain as much as the heartwood 
of the base of the trunk. The wood of coppice-grown 
oak is richer in tannin than that of high-forest grown 
oak, and generally the broader the annual rings 
are, the larger is the quantity of tannin. Alco oak grown 
on limestone soils yields more tannin than oak 
from a soil deficient in limestone. 
Another interesting result of Professor Henry’s 
experiments shows that the tannin in the bark and 
sapwood deteriorates and disappears much more rapidly 
than that in the heartwood ; in the first two it exists 
in the form of amorphous granules, which, in contact 
with water, first of all break up into minute globules 
and form an opaque mass, and finally become 
completely dissolved, whereas in the heartwood the 
tannin is found as a homogeneous deposit impregnating 
the membranes not only of the medullary rays, but 
also of all the fibrous tissues, and in this condition 
is better preserved. Even fossil oak wood contains 
some tannin, but fungi destroy the tannin completely, 
wood suffering from red rot containing no tannin 
at all. 
It is very desirable to have similar analysis made 
of our Indian trees, which contain sufficient tannin 
for the leather industry, but in the meantime we 
may presume that what M. Henry has found out 
for the common European oak is more or less true 
of all trees. 
I will now proceed to describe, first, the process 
of extraction treated in a general manner, and then 
briefly some of the more usual processes employed. 
Method of Extraction. 
I. — Generalities. 
Whatever the special method employed, the follow- 
ing is the order of the processes to be gone through ; — 
(1.) The wood or bark must be chopped up or 
shaved fine transverse to the grain, so that the fibres 
and vessels may be cut across. 
(2.) The chips or shavings, as the case may be, 
must be macerated or subjected to the action of 
hot- water or steam, so as to yield an infusion or 
decoction. As all natural waters contain lime, and 
lime diminishes the yield of tannin, either distilled 
Vrater must be used (expensive) or the water should 
be mixed with a small quantity of sulphuric or oxalic 
acid, in order that the lime may be precipitated, 
excess of acid being afterwards got rid of by the 
addition of an alkali in the form of a carbonate or 
caustic. 
(3.) The extract should next be cleared of the 
colouring pectosio and other matters in suspension. 
This is done either by treating with blood or any 
other albuminous substance, such as the coagulum 
of casein (blood has hitherto given the best results), 
or by filtering through animal charcoal (very wasteful, 
as the charcoal absorbs a large proportion of the 
tannin ), or by the addition of metallic salts, or 
by centrifugal force (on the same principle as that 
of the cream separator). Each and every system 
necessarily involves some loss of tannin. 
(4.) Mechanical filtration, preceded, if necessary, 
by decantation. 
(5.) Concentration to the degree required, if a 
liquid is wanted, or reduction to an earthy form 
like cutch. In either case the pneumatic process 
should be used. 
II. — Special Processes. 
It will suffice to describe here five processes, all 
of which "may be easily employed in India and 
require no expensive or special plant that cannot 
be made in the country itself. 
1. Gondola’s Process. 
The chips or shavings are macerated, with or without 
the application of heat, in water, to which sulphuric 
acid has been added at the rate of 6 grammes to a 
litre. The extraction of the tannin being complete, 
the infusion is treated with sodium carbonate, Z 
gramme for every G grammes of acid used. A 
precipitate forms which is got rid of by decantation. 
The extract thus obtained is not highly coloured • 
but in case a- lighter coloured and perfectly limpid 
fluid IS required, clarification must be undertaken 
with a coagulating substance. This latter must be 
mixed with the infusion at a temperature not exceed- 
ing 45° C. The temperature should then be quickly 
raised, the mixture being constantly and energeti- 
cally stirred. Caro must, however, be taken not to 
allow the temperature to exceed that necessary for 
coagulation, otherwise the albumen will remain in 
suspension and fail to absorb the colouriug mat- 
ters. As soon as coagulation is complete, the liquid 
must be allowed to cool. After a rest of about an 
hour it is drawn off and filtered and theu concen- 
trated to 30 to 45° Baum6, according to require- 
ments. The extract is very rich in tannin, is ex- 
tremely soluble, and is of the colour of honey. 
2. Another Process. 
When the wood or bark used is of a very deep 
colour, a slightly different process has to be employed. 
Macerate in water, adding at any time 20 grms,' 
blood for every kilog. of bark and wood and keeping 
the temperature well below 80° C. When the macer- 
ation is complete, the temperature of the liquid is 
to be brought down to about 55°C., and 1 grm. of 
carbonate of soda or of another alkaline salt and 
15 grms. of blood added to every litre of the liquid 
The temperature should now be raised, whilst con- 
stantly stirring and gradually adding 6 decigrammes 
of sulphuric acid for every litre of the infusion. The 
result is that a flocculent mass at once forms in the 
liquid, consisting of lime salts and colouring matters 
with the albumen. 
Cool, decant and concentrate as before. 
3. A Third Process. 
This is a slight modification of the preceding a 
sulphite or bisulphite being substituted for the sul- 
phuric acid and added duniuj, not after, the maceration. 
The salt is decomposed, tannates and free sulphurous 
acid being produced, the latter of which acts as a 
decoloriser, becoming thereby changed into sulphuric 
acid, which precipitates the lime salts in the water 
and prevents their alkaline action on the tannin The 
tannates or free sulphite or bisulphite, as the case 
may be, that still remain unused in the liquor are 
got rid of by tho addition of sufficient sulphuri^j 
