184 MR. B. 8CHUNCK ON THE 



groat 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 the shelf g and thus confine the current within a narrow 

 space. The current of air which I employed, and which was 

 sufficiently rapid 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 products 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 



* In the course of the investigation I had an opportunity of confirming a state- 

 ment made by the authors, who have described the cultivation of the woad plant 

 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 preceding one. This 

 may perhaps be ascribed to the lower temperature prevailing during the latter 

 part of the year. Nevertheless if the roots be left in the ground through the 



