On the Manufacturing of Indigo in this Country. 239 



er is the most difficult point in the whole process of making indigo ; 

 for should not the fermentation be carried far enough, a considerable 

 loss of coloring matter will be the result. It is necessary, therefore, 

 to carry it on to a certain point, and to draw it off tlie instant it ar- 

 rives at that point ; and this can be known only by a skilful observer 

 who has obtained his knowledge by practice. 



There is no chemical operation so difficult to describe as that of 

 fermentation, and I almost despair of making myself clearly under- 

 stood by practical workmen in the following description of the steep- 

 ing process. 



Fermentation has been divided by chemists into four kinds, the 

 panary, vinous, acetic and putrefactive. The kind of fermentation 

 given in the indigo steeper is evidently of that kind called panary, or 

 the first stage of fermentation. It is known to be the panary by the 

 large quantity of carbonic gas given out, which rising to the surface, 

 floats on the top, covered with a thin pellicle of the liquid. The 

 difficult point for the operator to distinguish is when it arrives at that 

 degree of fermentation, and begins to assume the acetic. The same 

 difficulty occurs with the woollen blue dyer, and the losses so fre- 

 quently complained of, by the vats being out of order, and often irre- 

 vocably lost, arise from the fermentation being permitted to proceed 

 too far. 



The following directions are given as a guide for those who may 

 be engaged in the making of indigo. Whilst the plant is in steep, draw 

 off a little of the water, and with a pen dipped in it make a few 

 strokes on white paper. The first will probably be high colored, 

 in which case the indigo is not sufficiently fermented. This opera- 

 tion is to be repeated every quarter of an hour, until it loses its color, 

 when it will have arrived at its true point of fermentation. 



Let a small hole be made in the stopper, six or eight inches from 

 the bottom, exclusive of the opening or aperture, for drawing off the 

 impregnated water. Let this hole be stopped with a plug, yet not so 

 firmly but that a small stream may be permitted to ooze through it. 

 After the plants have been steeped some hours, the fluid oozing out, 

 will appear beautifully green, and at the lower edge of the cistern, 

 from whence it drops into the battery, it will turn of a copperish col- 

 or. This copperish hue as the fermentation continues, will gradually 

 ascend upwards to the plug, and when that circumstance is perceived, 

 it is proper to stop the fermentation. 



