128 On Aerial Navigation. 



and intensity of the ambei'-coloured liquid whicli the indigo 

 produces, and this is found independently of any valuation of 

 the oxymuriate of lime. 



Some of the samples I have tried, and the results are as , 

 under : 



1. — Precipitated and sublimed indigo, each one grain, gave 

 neai'ly the same results. Each of these rec[uired 140 grains 

 of the oxymuriate of lime solution, corresponding to 25 parts 

 of a grain of oxj'gen. The yellow liquid obtained was 3G00 

 grains. 



2. — Flora mdigo, one grain, required 70 of the oxymuriate 

 = *125 parts of a grain of oxygen, or one half of the other. 



The same result from a sample marked J. R. best. 



3. — Indigoes marked 1 P and 3 P required about 60 of the 

 oxymuriate. 



4. — Those marked J. R. middle, J. R. •worst, and 4 P, re- 

 quired about 50 oxymuriate. 



5. — That marked Wood was rather inferior to the above, 

 but required above 40 oxymuriate. 



6. — Those marked 2 P and 1194 were the lowest I have 

 examined ; one grain of each did not require more than 30 

 oxymuriate, or 35 at the most. A poor turbid yellow liquor 

 was produced. The sample 2 P, when burned, yielded about 

 30 per cent of fine sand. 



Upon a review of these experiments, I am persuaded that 

 to destroy Indigo by oxymuriatic acid, twice the quantity of 

 oxygen is necessary that is required to revive it from the lime 

 solution. 



I hope the subject here taken up will not be considered as 

 unimportant, when we are informed that the article indigo 

 imported into this country annually, about fifteen years ago, 

 amounted in value to upwards of two millions of pounds ster- 

 ling; and it much exceeds that sum in all probability at the 

 present time. 



XXI. On Aerial Navigation. By A Correspondent. 

 To the Editors of the Philosophical Magazine and Jour 7ial. 

 Gentlemen, 



THE late passion for balloons has subsided without pro- 

 ducing any improvement, except a sensible hint in 

 one of the newspapers, that the aeronaut should carry with 

 him a long line having a great number of ropes attached, so 

 as to increase the chance of assistance from below. Yet I 

 think it will appear that the direction of tliese machines, 

 . . ■ thouoh 



