12'2 Mr. J. Dalton on llw Nature and Pi-opertics of indigo. 



of Ticsan wliich I liave made known, leaves no further doubt 

 respecting the existence of sulphur in the primitive districts. 

 It has also been lately found in Brazil, that the chloritic 

 quartz formation which covers, in the Capitania de Minas 

 Geraes, the primitive clay-slate, contains both gold and sul- 

 phur. Laminae of this rock strongly heated burn with a 

 blue flame. Near to Villarica, in the district called Antonio 

 Pereira, a schist, of the same age as that on which is super- 

 posed the itacolumite or chloritic quartz, contains a calca- 

 reous betl traversed by veins of quartz, which the Baron d'Esch- 

 wege (director of the gold and diamond mines of these coun- 

 tries) has found filled with little nodules of pulverulent sulphur. 

 All these phaenomena increase in interest, when we reflect that 

 this learned geologist, and also another German traveller 

 (M. Pohl) incline to the opinicm that gold, micaceous iron, dia- 

 monds, euclases, platina, and palladium, which are peculiar 

 to the alluvial districts of Brazil, have been derived either from 

 the destruction of the great formation of chloritic quartz, or 

 from that of a ferruginous bed {itabarite) which is placed above 

 this formation. 



XX. On the Nature a?id Pro^jerties of Indigo ,- xvith Directions 

 for the Valuation of different Samples. By John Dalton, 

 Esq. F.B.S. S,r.* 



Vl/^E owe the first good approximation to die chemical ana- 

 Ij'sis of the indigo of commerce to Bergman. Accord- 

 ing to his experiments, the best samples of indigo yielded, by 

 analysis, the following principles : 

 47 pure indigo 

 12 gum 

 6 resin 

 22 earth 

 1 :i oxide of Iron 

 100 

 A subsequent analysis of indigo made by Chevreul [Annal. 

 de Chimie, t. 68), gives 45 percent oi" pure indigo in the best 

 Guatimala indigo, and the foreign matters much the same as 

 by Bergman, but diffeiing considerably in the proportions. 

 Indeed it is most probable that the foreign matters will be 

 found to differ materially, both in quantity and kind, from the 

 various modes and circumstances of the manufacture as prac- 

 tised in different places, and perhaps from the various species 



* From thf Mciiiniis of the Mterary and Phildsopliiral Sodclv of Man- 

 chester. 



of 



