THE TROPICAL A&MCULTURIST. [July 1, 1903. 
simple organic bodies, and simple organic bodies 
Uitially more so than inorganic bodies, and this, is 
one of the reafons vshich is likely to canfe the 
inorganic chrome tanning to supersede the old organic 
tanning. 
For a long time it was expected that chromate 
salts would prove the best ingredients for tanning, 
for they have a strorgly oxidizing power in them- 
selves, and organic matter has a strongly deoxidizing 
power on Ihem ; but for a very long time atternpts 
to utilize them were unsuccessful. Dr. Heinzerling, 
a German chemist, appears to have been the first 
to work them successfully ; and it is probable that 
the present American chrome-tanning is nearly a 
modification of his process. Thst process consisted 
in the use of bichromate of potash, chloride of 
potash or soda, and sulphate of alumina, mixed 
together in a large stock tank, and drawn off as 
required by a system of piping communicating with 
each pit. As in ordinary tanning, the solution is 
at first made very weak, but is strengthened syste- 
matically every few days according to the thickness 
of the hides to be tanned ; the quantity of chromic 
acid used being from 2| to 5 per cent of the weight 
of the leather produced, and the cost from one to 
three shillings per 100 lb. of leather. The skins 
thus prepared are of a yellowish colour; and, at 
this stage, are dipped into chloride of barium which 
converts the soluble chromates into insoluble chro- 
mate of barium, and adds to their weight and 
solidity. They can then be coloured to any suitable 
colour, after which they are allowed to nearly dry 
and are then immersed in pure paraffin wax and 
resins which tend to make them waterproof. It 
is alleged that the use of paraffin and fatty matters 
reduces chromic acid to chromic oxide, the oxygen 
liberated iu the bide oxidizes the fatty into acid 
bodies, and these acid bodies unite with the chrome 
oxide to form a third insoluble compound mordanted 
in the fibre of the leather, making it at once supple 
and waterproof. 
It is an open question as to whether chrome 
tanning will ultimately supersede ordinary tanning 
or not. There are many points in its favour ; the 
most important, as pointed out above, being that 
the inorganic compounds are more stable than the 
organic compound. Another point that is usually 
put forward in its favour is the rapidity of the 
operation, about as many days being required for 
chrome tanning as weeks are necessary for ordinary 
tanning ; at the same time it is doubtful whether 
the short period of preparation is really as good 
as the longer older process, by which the skins 
become seasoned from the very length of the process. 
Then again the skins in the chrome process are 
artificially weighted by using the salts of the very 
heavy metal barium, and it is doubtful whether this 
is a real benefit. Again, bichromate of potash is 
at present cheap, but considering that some four 
to five hundred thousand tons of tanning material 
are used annually in Great Britain alone, and con- 
sidering that there is a large demand of bichromate- 
of potaeh for pigments as well, it is doubtful 
whether such demand would not raise the prices 
to an unprofitable extent. 
If the chrome tanning does supersede the ordinary 
tanning, it will be a serious matter for India, not 
only in respect of the tanned skins that are exported 
in such large quantities, but also in respect of tanning 
materials themselves, for it is only recently that 
the tanning substances are being taken in hand 
and studied sj stematically. There are upwards of 
200 Indian trees which produce tannin in some of 
their parts ; the bulk of these tannins are produced 
by barks, and belocg to the catechol class; they 
are mostly high coloured, and in the form of bark 
are far too bulky for export remuneratively, but 
there is not the slightest reason why as extracts a 
very much larger trade might not be carried on. 
Ab previously pointed out, the great desiderata for 
good tanning material are, high percentage of tannin, 
low percentage of non-tannin, and good, or but little 
colour. Bark, as bark, seldom contains more than 
20 per cent of tannin, but as extract often con- 
tains 50 per cent, and in some cases rises as high 
as 70 or 80 per cent. Many attempts have been 
made to decolourise extracts, and the operation has 
met with a fair amount of success ; perhaps one 
of the best methods is by the use of alkaloids, for 
it has been found that the alkaloidal residue in 
quinine manufacture, a waste product, will serve the 
purpose ; if added in very small quantity at first 
the colouring matter is removed, and for the ad- 
dition of the alkaloid completely precipitates the 
tannin. Casein, and ferrocyanide of potassium and 
other processes have also been adopted. 
The various tanning materials used in Europe 
and America have each their peculiar quality 
with respect to firmness and solidity, softness 
colour, scent, toughness, or power of resisting 
moisture and decay. It will be as well to review 
them and the Indian materials together in the 
following categories : (1) Barks, (2) fruits, (3) leaves, 
(4) galls, and (5) extracts. 
(l^ Ilat-Jes.- The most important are the oak 
barks, used chiefly for sale leather as they contain 
quercitannic acid and phlobaphen which give solid 
deposits, some 200 to 300 thousand tons (tannin 
about 10 per cent) being consumed annually in 
Great Britain. In America the chestnut oak. Quer- 
citron oak, red oak, and white oak are used for 
the same purpose, and in Northern India there are 
four good oak barks, one — Quercus in cana — having 
22 per cent of tannin. The everygreeu or holm 
oak of Southern Europe ia used to give sofffness, 
"Wattles, or mimosas, are the produce of Australian 
acacias, whish yield from 18 to 34 per cent of 
tannin, and are imported to the extent of some 
30,000 tons, but they are not so much appreciated 
as the oaks, as they are said to produce a dark 
hard and somewhat brittle leather. To the same 
genus belong the Indian Black babnl with 30 per 
cent of tannin, white babul with from 9 to 21 per 
cent, and a troublesome climber of most open forests 
that have been fired {A, pennata ) with about 9 per 
cent of tannin. To the same family belong the 
cassias, two of which ( C. auriculata and Fistula) 
are perhaps the most commonly used tanning barks 
of Southern India, the former being the Tangedu 
or Avaram; also in the same family are Albizsias, 
Bauhmias, Butea, Dalhergias, JEryihiina, Entada, 
Hardwichia, Ougeinia, Prosopis, Pterocarpus and Xylia, 
common trees with a very fair proportion of Cate- 
chol tannin. Most of the nim or margosa family 
produce tannin barks, the most important being 
perhaps the Carapa with 35 per cent of tannin, whilst 
Soymida (13 p. c.) is largely used in Southern India 
and gives a light coloured leather, Toon ( Cedrela) 
giving a purple leather. Many of the niango family 
also are important in this respect, mango itself giving 
17 per cent, but perhaps the most valuable being 
Bhusmysorensis, a common shrub in Mysore and 
the Coimbatore hills, which gives 16 per cent and 
furnishes a splendid brown or buff-coloured leather. 
The next important group are the mangroves that 
grow in tidal creeks, which are said to make most 
durable sole-leather, even better than oak, but 
there appears to be a prejudice against this tannin 
in England. Associated with the mangroves are 
often found Heritiera, Someratia, and Avicen7iia, all 
tan producers; and on the sandy stretches near 
them are frequently Tamarisks. Most of the Ter- 
minalia species, the producers of myrabolans, furnish 
tan-barks, and Auogeissas in the same family, a 
most plentiful tree in Southern India gives 32^ per 
cent. The Blue-Plums (Eugenia) are tanniferous, 
as are many other members of the same family, 
e.g., Guava, Oareya, Barringtonia, Myrtle, and 
Hill Guava. Casnariua givesj from 7 to 18 per cent. 
