On Indigo. 437 
agitated repeatedly, letting in water each 
time, instead of oxymuriate of lime, because 
T was aware that the 100 measures already 
in the tube were not saturated. Soon after, 
the process was at an end, no more nitrous 
gas being absorbed. The 100 measures of 
the oxymuriate took 168 measures of nitrous 
gas to saturate them. Now deducting ., of 
this for the nitrous gas impregnating the 
liquid, and for loss occasioned by the free 
oxygen gas in the water which the nitrous 
gas had to combine with, there will remain 
157 nitrous gas = .2 grain weight, which 
was converted into nitric acid; but if we 
deduct + part froin the weight of nitrous gas, 
we shall have the weight of oxygen requisite 
to convert it into nitric acid = .175 parts of 
a grain; only differing -2,, from the other 
valuation by sulphate of iron. 
To find the value of any sample of Indigo, 
I take one grain carefully weighed, from a 
mass finely pulverized. I put this into a 
small glass, a wine-glass for example; then 
by a dropping tube I put 2 or 3 grains of 
concentrated sulphuric acid upon it. The 
two principles are next well mixed together 
by trituration with the end of a small glass 
rod. Water is then poured in and the co- 
louring matter fully diffused through it. 
