Mr, Daiion on Indigo. ^QH 



Ifie 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 regetable, con- 

 tributed to give the wooded heights, while the streams were 

 more animated and cheerful, from their clearaess, rapidity, 

 and pebbled beds, so different from the sluggish and muddy 

 waters of the plains, their unvaried surface and monotonous 

 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 inio a wine-gla^s, 

 and drop two or three drops of concentrated sulphuric acid 

 upon it. Having triturated them well, pour in water, and 

 transfer the coloured liquad 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 af oxy-muriate of iime 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 trjan?- 

 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, and a drop of dilute sulphuric acid; if 

 more 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, 

 Mr. 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. 

 Vol. IX. No. 2, 49 



