Experiments on Ind'ujo. 275 



At length, by adding a little caustic potash to absorb the 

 carbonic acid which might be generated, the diminution of 

 oxygen became apparent, and in a few minutes all the oxygen 

 contained in the eudiometer tube disappeared, the tube being 

 too small to supply enough for saturation. 



As the employment of potash was on some accounts objec- 

 tionable, I also tried and succeeded in another method of 

 obviating the presence of carbonic acid. 



In a glass balloon, furnished with a stopcock, a vacuum was 

 made, into which the liquid was suddenly introduced by a con- 

 necting tube. By this means a great deal of gas was separated, 

 and, by repeating the action of the air-pump, much of what 

 remained was withdrawn. 



To the vacuum above the liquid, pure oxygen was admitted 

 from a mercurial gasometer, its quantity being measured ; and 

 the air in the balloon was further analyzed by withdrawing a 

 small portion. The balloon was then agitated, and water from 

 time to time admitted to replace the oxygen which had been 

 absorbed. The residual gas was again analyzed, to find whether 

 the carbonic acid or azote had altered in quantity during the 

 experiment, and the weight of the oxygen absorbed was ascer- 

 tained from that of the water which had entered the balloon. 



Four experiments conducted in this manner, yielded the 

 following results : — 



1 Expt. 2 Expt. 3 Expt. 4 Expt. 



Weight of liquid grains, 8455 5500 5166 6478 



Weight of oxygen absorbed, 2.00 0.82 0.84 1.22 



Weight of Indigo collected, 6.8 2.9 3.9 4.9 



Proportion of oxygen in the] 



29.4 28.2 21.5 25.0 



Indigo per cent. 



\ 



Making an average of 26 per cent, of oxygen absorbed ; a 

 quantity nearly double what Crum supposes to exist in pure 

 indigo, and an average between that which he ascribes to 

 cerulin and phenicin. It is, however, little more than the 

 half of what Thomson states in his analysis. 



There is hardly any occasion to seek a nearer concurrence 

 between experiments made in the manner just described on 

 the liquid of the vats ; because the indigo forms but a very 

 small proportion of the matter held in solution therein, and it is 



