Di". Schunck on the Formation of Indigo-blue. 81 



grooves fixed to the sides, which in a great measure prevents 

 the dust which is carried along by the current of air from being 

 conveyed into the liquid. The apparatus is now placed so as to 

 make the back fit as closely as possible to the wall, q r, fig. 2, in 

 which there is an opening, s, communicating with a steam-boiler 

 flue ; or the back of the box may be closed with a piece of wood, 

 having an opening communicating by means of a pipe with the 

 flue. The section, fig. 2, shows the direction taken by the air in 

 passing over the surface of the liquid. As the liquid evaporates, 

 the dish is raised by means of additional supports so as again to 

 bring the surface of the former close to tlie shelf g, and thus 

 confine the current within a narrow space. The current of air 

 which I employed, and which was sufficiently I'apid to cause a 

 constant ripple on the surface of the liquid, was produced by 

 the draught of a steam-boiler flue, which carried away the pro- 

 ducts of combustion from several large fires. I think it probable, 

 however, that the same effect might be produced by causing the 

 whole of the air necessary for the supply of an ordinary stove or 

 close fireplace to pass through the apparatus. By means of the 

 current of air at my disposal, I was enabled to evaporate in this 

 apparatus about one pint of water in the course of twenty-four 

 hours at a temperature not exceeding 10° C, the temperature of 

 the water being kept by means of the rapid evaporation rather 

 lower than that of the atmosphere. The evaporation of a gallon 

 of spirits of wine by the same means occupied only a few hours. 

 In preparing indican, the course of proceeding which I adopt 

 is as follows*. The dried woad leaves are reduced to a powder, 



* In the course of the investigation I had an opportunity of confirming 

 a statement made by the authors «ho have described the cultivation of the 

 woad jilant and the preparation of the dye made from it, viz. that the first 

 crop of leaves obtained during the first year's growth of the plant is richest 

 in colouring matter, and that each successive crop yields less than the jirc- 

 ceding one. This may perhaps be ascribed to the lower temperature pre- 

 vailing during the latter part of the year. Nevertheless if the roots be left 

 in the ground through the winter, though the plant in the ensuing year 

 seems to have lost none of its vigour, as may be seen by the size aud abun- 

 dance of rich glaucous leaves which it puts forth, and the quantity of flower- 

 stems bearing numbers of flowers, and then of seeds which it sends up, 

 still the leaves arc as jioor in colouring matter as those of the preceding 

 autumn. The inferior (piality of the dye produced from the second year's 

 leaves, which in Thuringia went by the name of " Komjjts-waid " (see 

 Schreber's Bcschreibuiiy des H'aids), was well known to the growers of 

 woad in fonner times. 



Woad is still em|)loyed by the woollen-dyers in tiiis country, but what 

 useful purpose it answers in preference to an e(iuivalent quantity of indigo, 

 I am unable to say. A specimen of tlie drug, as used by a wr)()llen-<lyer. 

 which I examined, contained no trace of indigo-blue. If its use be merely 

 to act as a ferment and reducing agent on the indigo em])!oyed at tiu' same 

 time, as is very probable, its ])lace might be sup])lied by rotten cabbage- 

 leaves or decaying vegetable matter of any kind. 



