31 1 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. [December ?5, 1871. 
oxygen, and "becomes insoluble blue indigo. The prin¬ 
cipal class of goods to which this chemical reaction is 
-.applied is to the vegetable fibres, linen and especially 
cotton. As far as dyeing is concerned, the processes can 
be classed under two heads, hot and cold. The hot pro¬ 
cess is principally applied to wool, the cold to vegetable 
fibres, especially cotton. 
The oldest and still most generally employed method 
•of preparing cold vats consists of putting into a vat 
containing about two thousand gallons of water, sixty 
pounds of indigo, very finely powdered, one hundred and 
eighty pounds of slaked lime, and one hundred and 
twenty pounds of sulphate of protoxide of iron or green 
vitriol (free from any trace of copper salt), the two 
latter substances being added from time to time. The 
greater part of the lime used unites with the sulphuric 
acid of the iron salt, to produce sulphate of lime or 
.gypsum, and the liberated protoxide of iron removes 
the oxygen from the indigo, becoming converted into 
saline oxide, whilst the reduced indigo dissolves in the 
excess of lime employed. 
Messrs. R. Schloesser and Co., of Manchester, have 
introduced within the last year or two a marked im¬ 
provement in the preparation of cold vats, which re¬ 
moves the great objections of the bulky precipitate of 
.sulphate of lime, the formation of an oxide of iron, and 
the loss of indigo by its combination with the oxide of 
iron referred to in the previous part of the lecture. The 
bath remaining much more fluid, the pieces are less apt 
to be spotted, and a better class of work is produced. 
To carry out their process, they add to the ordinary two 
thousand gallon vat twenty pounds of ground indigo, 
thirty pounds of iron borings, thirty pounds of their 
remarkable powdered zinc, and thirty-five pounds of 
■quick lime; the whole is stirred up from time to time 
for twenty-four hours, when it is ready for use. If the 
~bath is not considered sufficiently strong, a little more 
lime and zinc are introduced. 
The chemical theory of the process is, that the zinc, 
Tinder the influence of the lime, decomposes water, com¬ 
bining with its oxygen, and the hydrogen thus liberated 
removes oxygen from the indigo, which then dissolves 
in the lime. 
To dye cotton yarn in the above vats, it is simply 
necessary to dip it for a few minutes in the dye-bath, 
-and expose it to the atmosphere, when the green hue it 
has acquired passes rapidly into blue. This operation is 
repeated until the yarn has attained the required depth 
■of shade, when it is passed into weak vitriol, washed, 
and is ready for market. 
To dye calicos, the pieces are hooked on frames, passed 
through a bath of weak milk of lime, and then dipped 
into the reduced indigo vat. After fifteen minutes, the 
•frame is taken out and the cloth exposed to the air for 
about the same length of time. It is again dipped, the 
process being repeated until the required depth of tint 
is attained. It is then passed through weak vitriol, and 
washed. The cold vats are especially used when it is 
wished to obtain white and yellow designs on a blue 
.ground; but when the object in view is to produce a 
•self-colour, a more rapid process is adopted. This 
consists in passing the pieces through a dye-beck, then 
through an acid liquor, and lastly in water, by means of 
rollers fixed in the vat. The bath is composed of lime, 
sulphate of iron and indigo, but is kept hot, instead of 
■cold, as in the former case. 
There is still another process, which is now used to a 
limited extent only, but was at one time very extensively 
•employed. It produces on the cloth a pale blue, which 
bas a great similarity of tint to that seen on the china 
porcelain, from which it derives its name of china-blue. 
To produce it the pieces are printed with a mixture con¬ 
taining very finely-powdered indigo and a little acetate 
■of iron, and are made to pass through six successive 
vats. The first two contain lime, the third sulphate of 
iron, the fourth a solution of caustic soda, the fifth a 
dilute solution of sulphuric acid, and the sixth water. 
When the design has acquired t ie required depth of 
blue, the pieces are washed, passe 1 once more through 
weak sulphuric acid, and again washed. The chemical 
reactions are exactly similar to those in the cold vat 
process. 
For dyeing wool, a modification of the old woad vat 
is employed. The use of woad being now almost entirely 
discontinued, I shall merely call your attention to the 
process in which indigo has been substituted for woad. 
It bears the name of Indian vat, doubtless from the pro¬ 
cess having been practised in India and imported from 
thence. It is as follows:—Eight pounds of powdered 
indigo is added to a bath containing 3| pounds of bran, 
3 ^ pounds of madder, and 12 pounds of potash, which is 
maintained for several hours at a temperature of 200° 
F. It is then allowed to cool to 100° F., when fermenta¬ 
tion ensues. After about forty-eight hours, the indigo 
is rendered soluble, being reduced by the decomposition 
of the sugar and other products contained in the bran 
and the madder-root during the process of fermentation. 
The bath should have a greenish-yellow appearance, 
having a frothy scum of a blue coppery hue. 
Of late years, improvements have been made in this 
class of vats, by which the expense of using madder is 
avoided. They are now prepared by adding to water, 
at a temperature of 200° F., twenty buckets of bran, 
twenty-six pounds of soda crystals, twelve pounds of 
indigo, and five pounds of slaked lime. After five hours, 
the bath is allowed to cool to 100° F., when fermenta¬ 
tion ensues, and the indigo is dissolved in the alkali. The 
management of these vats requires great experience and 
care, for if the fermentation is too slow the indigo is not 
properly reduced, whilst if too active large quantities of 
indigo may be lost. The researches of Dr. Schunck, 
already referred to, not only show the method of avoid¬ 
ing this loss, but explain why it occurs. The remarks 
which I made as to the causes of failure in the manufac¬ 
ture of indigo are applicable here, namely, that if the 
fermentation becomes alcoholic and acetic, the non- 
oxidizable indigo compounds described by Dr. Schunck 
are generated. 
I cannot leave the subject of indigo without bringing 
before you a most curious source of its production, 
namely, the human body. Medical men had observed 
from time to time that urine, secreted under certain 
pathological conditions, became brown, and sometimes 
even blue, when exposed to the atmosphere. The late 
Dr. Hassel discovered that in some instances the colour¬ 
ing matter was indigo, but here, again, we are indebted 
to Dr. Schunck for much information on the subject. 
In three papers presented to the Royal Society, he has 
proved that urine, in cases similar to those examined by 
Dr. Hassel, contained the glucoside of indigo, or indican. 
He also observed that indican was a very frequent con¬ 
stituent of urine secreted by persons in a healthy state, 
and, in fact, that it is produced generally when persons 
do not take sufficient exercise, and he has on several 
occasions succeeded in producing it by taking in his food 
a rather large excess of sugar. 
Orchil , Cudbear , Litmus .—I shall now call your atten¬ 
tion to a colour which was discovered in 1300, by an 
Italian named Federigo, who, during his travels in the 
East, observed the tinctorial powers of a certain class of 
weeds called lichens , and he introduced the colour into 
Florence under the name of orchil. By this discovery 
he and his family made a very large fortune. 
Lichens are small plants which live either in the stems 
or leaves of trees, or on rocks, or damp soils. To this 
class belongs all the vegetation found in the Arctic 
circle, but the species growing there are not employed 
to produce the colouring matter orchil, the varieties used 
for this purpose being found in warmer, and especially 
in tropical climates. These latter can be divided into 
two classes; the first and most abundant, which grow on 
rocks near the seaside, includes the species Eoccella tine - 
