Acid of Indigo. " 233 | 
was wanted, I believe, to decompose for the manufacture of car- 
bonate of soda. ) 
On showing him some that had lain many months in a large 
old wrought-iron boiler (which formerly belonged to a steam- 
engine) he was delighted with a beautiful white effloresence which 
appeared on the sides of the boiler nearest in contact with the 
refuse, and which he ascertained afterwards to be a carbonate of 
soda combined with a very small portion of iron. 
Last week I was much pleased to hear from him that he had 
succeeded in obtaining this carbonate, by placing some scraps of 
jron in contact with crystals of sulphate of soda for six weeks. 
“Tt is well known that the bleacher’s refuse is principally a sul- 
phate of soda and manganese.” 
I hear with very considerable pleasure that Mr. Jephson is pre- 
paring for publication a work entitled ** The Elements of Che- 
mical Analysis ;” and if my expectations are realized, it will do 
him much credit. 
Quere. Could a manufactory of carbonate of soda be con- 
ducted by the above process ? 
ACID OF INDIGO. BY PROFESSOR VAN MONS. 
It has been hitherto believed that in the blue tub the indigo 
loses its colour by becoming deoxidized; and resumes it on ex- 
posure to the air by being reoxidized. M. Doebereiner has as- 
certained that it experiences this effect by becoming hydroge- 
nated in the tub, by the combined reaction of oxidulate of iron, 
lime and water, and by being dehydrogenized on exposure to 
the air, and more rapidly by a weak solution of chlorine. Indigo, 
which has the same constituents as animal charcoal, viz. thirty- 
six parts of carbon with three parts and a half of azote, forms in 
becoming hydrogenized a colourless acid soluble in water. This 
acid combines in the tub with the lime, and separates itself 
anew under its ordinary form of indigo, when by the oxygen of 
the air, or that of the chlorine,its hydrogen is resolved into water. 
M. Doebereiner has named the acid of indigo isatanic, and its 
combination with lime zsatinate. 
M. Holt has subsequently observed that the filings of iron or 
of zine, being put into a solution of indigo in sulphuric acid, dis- 
colour that solution; and he thinks that this effect is caused by 
the hydrogen which these metals detach from the water. It is 
already known that sulphurated acid, also prussiarated hydrogen, 
effects a similar discoloration. The indigo here manifests with 
the hydrogen a stronger affinity than with the sulphuric acid ; 
and this affinity cannot be weak, since it counterbalances that 
which at the degree of heat which excites it the hydrogen never 
fails to exercise upon the oxygen of sulphuric acid. 
NEW 
