240 
THE ACTION OF SULPHURIC ACID ON INDIGO. 
leather or other material of the ordinary 
kind and may be carried by the sieve roller, 
mandril, blanket, or principal carrying wheel. 
The advantage to be derived by my plan, is, 
that I can make the work completely perfect 
with a surface pattern roll of any circum- 
ference without regard to the size of the man- 
dril or principal carrying wheel, and if a sur- 
face pattern has become untrue it may be put 
into the lathe and turned true, turning at 
the same time either or both ends of the pat- 
tern roll which the belt or belts pass over ; 
the spoiled rolls, which were formerly a com- 
plete loss, may thus be put again into working 
order, and the large expense for new rolls is 
entirely saved ; also by this mode of printing 
the immense expense of copper rolls used in 
cylinder printing may be saved, the improved 
surface-machine being rendered capable of 
executing the work equally well, and some 
styles and patterns much better, and at one 
fourth of the cost for rolls and patterns ; 
this invention also enables me to work any 
number of rolls upon the surface-machine, 
each roll printing a separate colour at the 
same time, by which method a full chintz may 
be produced at one printing. 
(To be continued.) 
EXPERIMENTS ON INDIGO. 
(Continued from page 192.^ 
The best radiators do not appear to belong 
to any particular class of bodies.; litmus blue 
and Prussian blue are side by side, while sul- 
phuret of lead, and the bi-sulphuret of tin, are 
fifteen numbers apart. 
If the results be admitted as decisive of the 
radiating powers of the bodies used, they show 
that each substance has a specific power not 
depending upon chemical composition, nor 
upon colour. I do not claim to found such a 
conclusion upon the experiments ; their ob- 
ject has been before 'Stated, and if they shall 
prevent the introduction of an inference from 
an imperfect induction, as a law of science, 
the labour bestowed upon them will be am- 
ply recompensed.* 
The action of sulphuric acid on indigo was 
very incorrectly described by the older che- 
mists. In the year 1776, Bergman observed 
that when indigo in powder was sprinkled 
upon concentrated oil of vitriol, sulphurous 
vapours were evolved, clouds of a green co- 
lour formed in the liquor, and at the same 
time great heat produced. Berthollet, in his 
excellent work on Dyeing ( Hamilton’s trans- 
lation, vol. ii. p. 66), considers the change 
which takes place to be caused by a species 
of combustion, the acid furnishing the indigo 
with oxygen. Dr. Bancroft conceived the 
solution to be oxygenated indigo in combina- 
tion with sulphuric acid, the acid becoming 
first yellow and then green, owing to the union 
* The scientific reader need not be reminded 
that these remarks do not bear upon the ra- 
diation or absorption of heat accompanying 
light. 
of part of the oxygen of the indigo with 
part of its hydrogen determining the formation 
of water ; he supposed that when it is there- 
by rendered soluble, it enters into a triple 
combination with the oxygen and sulphur 
composing the acid, regaining its blue colour 
witli additional brightness either from its union 
with an increased proportion of oxygen, or 
from some effect resulting from the sulphur 
which had not been combined with it origi- 
nally. Dr. Bancroft also observed, that after 
being dissolved by sulphuric acid, the indigo 
can never be restored to its origina 1 state ; he, 
therefore, calls the whole sulphate of indigo. 
This was all that was known on the subject, 
when Mr. Crum commenced his researches, 
which may be found in the Philosophical 
Transactions for January, 1823. Having 
carefully repeated his experiments, together 
with the more recent ones of Berzelius, and 
having made a few observations myself on the 
various attendant phenomena, I propose to 
lay them before your readers. 
It is only when impure indigo is employed 
that sulphurous acid is generated during the 
solution of that substance in sulphuric acid 
with either precipitated or sublimed indigo ; 
although there is probably a decomposition of 
the acid, there is no indication of it ; heat is 
invariably produced, and I think it is pretty 
evident that water is formed, and that the 
oxygen and hydrogen gases are furnished by 
the indigo, because the blue colour is always 
restored by the addition of water. The in- 
digo during solution undergoes a change 
which is more or less complete, according to 
the time the substances ,are left together and 
the degree of temperature to which they are 
exposed. In about 24 hours, at the ordinary 
heat of summer, the indigo is converted into 
a new substance, for which Mr. Crum has 
proposed the name of cerulin. 
To produce cerulin, I digested precipitated 
indigo for six hours in very highly concentra- 
ted sulphuric acid, and then poured the thick 
blue liquor into distilled water, sulphate of 
potash* precipitated a dark blue substance, 
which was thrown on a filter, and washed 
with a solution of acetate of potash, t and sub- 
sequently with alcohol ; while wet, the new 
substance had a dark blue colour, but when 
dry it was copper colour. Mr. Crum calls it 
coeruleo-sulphate of potash. W hen a portion 
was burnt, no purple fumes were formed, but 
a considerable quantity of ashes remained ; 
it was highly deliquescent, 3 grains acquired 
in 5 hours, by exposure to the air, nearly |^th 
of a grain in weight. I made a great many 
experiments to ascertain by what salts it was 
precipitated when dissolved in water, the so- 
♦ Potash itself and some other neutral salts 
have the same eflFect. 
t Mr. Crum ascertained that cerulin is not 
soluble in any salt of potash, although it is al- 
most to any extent in hot water; he recom- 
mends the acetate as possessing the advantage 
over the muriate or sulphate of not beiu« pre- 
cipitated by alcohol from a weak solution in 
water as they are. It may consequently be 
afterwards removed by washings with alcohol. 
—See note DD to the 2d volume of Uie’s Trans- 
lation of Berthollet on Dyeing. 
