Mr. Dalion on Indiga. 885 
the alterations of atmospherical pressure in any accessible 
part of the Himalayah and Calcutta are cotemporaneous? 
It were vain to attempt describing the enthusiasm and de- 
light experienced by the admirers of nature, on first entering 
these districts. Inhabitants of the north, long exiled from the 
place of their birth, and contending with the fiery atmosphere 
of the tropical regions, can alone conceive the pleasure which 
many derived from the approach to a northern climate, and 
the gradual appearance of the features of a northern land- 
scape, which the pines, more than any other vegetable, con- 
tributed to give the wooded heights, while the streams were 
‘more animated and cheerful, from their clearness, rapidity, 
and pebbled beds, so different from the sluggish and muddy 
waters of the plains, their unvaried surface and monotonong 
productions. 
23. Mr. Dalton’s process for determining the value of Tn~ 
digo.* In order to find the value of any sample of indigo, 
Mr. Dalton directs us to take one grain carefully weighed 
_. from a mass finely pulverized. Put this into a wine-glass, 
: and drop two or three drops of concentrated sulpburic acid 
upon it. Having triturated them well, pour in water. and 
transfer the coloured liquid into a tall cylindrical jar, about 
one inch inside diameter. When the mixture is diluted with 
water so as to show the flame of a candle through it, mix the 
liquid solution of oxy-muriate of lime with it, agitating it slow- 
ly, and never putting any more in till the smell of the pre- 
ceding portion has vanished. The liquid soon becomes trans- 
parent, and of a beautiful greenish yellow appearance. After 
the dross has subsided, the clear liquid may be passed off, and 
a little more water put into the sediment, with a few drops of 
oxy-muriate of lime, anda drop of dilute sulphuric acid; if 
mere yellow liquid is produced, it arises from particles of 
indigo which have escaped the action of the oxy-muriate be- 
fore, and must be added to the rest. The value of the indigo, 
r. Dalton considers to be in proportion to the quantity of 
real oxy-muriate of lime necessary to destroy its colour. He 
is of opinion, also, that the value may be well estimated by 
the quantity and intensity of the amber-coloured liquid which 
the indigo produces, which is found independently of any va- 
* This article, and the five next succeeding, are copied from Dr. 
Brewster’s Edin. Journal of Seience, Vol. II. 
Vou. IX. No. 2. An 
