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JOUENAL OF THE EOYAL HORTICULTUKAL SOCIETY. 



cause of this. If these plants be treated with boiling water the enzyme 

 is destroyed and indican solution is obtained, which, if microbes be 

 excluded, will keep undecomposed ; but the addition of this indigo enzyme 

 and certain yeascs, as well as boiling vdth. acids, convert it into indoxyl 

 and sugar. 



Woad, on the other hand, is an indoxyl plant which always yields an 

 indoxyl solution either to hot or cold water, but it is necessary to keep the 

 air excluded, as this indoxyl is so easily oxidised and the indigo-blue lost. 

 For the extraction of indoxyl, he recommends that a wide-mouthed 

 stoppered bottle be filled with "Woad leaves and hot water poured in, the 

 leaves are then pressed down so that all the air is expelled and the stopper 

 put in, in such a manner that no air bubble is left between the top of 

 that water and the stopper. In the course of a few hours a clear pale 

 yellow liquid can be decanted which is rich in indoxyl ; the addition of an 

 alkali and blowing through the liquid causes the precipitation of indigo- 

 blue. The addition of one of the stronger acids, in a diluted state, acts, 

 however, more rapidly than the carbonic anhydride. The infusion is 

 yellow with a green fliiorescence. The result of this experiment with 

 Parson Drove Woad was eminently successful, the infusion was beautifully 

 fluorescent ; by transmitted light it was pale sherry coloured, but pale 

 green by reflected light. On the addition of an alkali it tiu-ned greenish 

 yellow, and when a few drops of dilute hydrochloric acid were let fall 

 into it an abundant precipitate of the long-looked-for indigo-blue took 

 place. So that after all the extraction of the blue colour of Woad is 

 absurdly simple, if one knows how to do it and goes the right way to 

 work ! One must, however, be very careful in several particulars, or 

 instead of a blue, a black precipitate will result. In the first place the 

 Woad leaves must be fresh ; in the second place they must be young, or 

 rather they must be actively growing. It is useless to manipulate old 

 leaves. In English Woad culture, the details of which are given in Mr. 

 Darwin's paper previously referred to, and even more fully in that by Mr. 

 Corder * (together Avith much other highly interesting information), the 

 method of gathering the crop consists in wrenching off the leaves by a 

 grasp of the hand, so that not only the old but a few of the growing 

 leaves are included ; hence an infusion of the cropped plant yields more 

 or less indigo, although if a larger percentage be desired only the youngest 

 leaves must be used. Then, as to the temperature of the water ; I find 

 that not quite boiling answers best, say about 80^-90° C. There is no 

 need to follow the elaborate details of excluding the air entirely, but if 

 the nearly boiling water be poured on the leaves so that they are quite 

 covered by it, the result will be perfectly satisfactory — provided the 

 infusion be not left too long. Half an hour to five or six hours is quite 

 long enough : after that you get the annoying black deposit which is the 

 bete noire of the Woad experimenter. If the water be left some hours on 

 the leaves it acquires a reddish tinge. The infusion is best when it is a 

 pale yellow as above described. If to this be added, when it is cold but 

 .before it has stood too long, an alkali, either lime-water or caustic potash 

 or soda or ammonia, the fluid becomes darker and greenish. Any woollen 



* Covder, E., "On the Culture and Preparation of Woad at Parson Drove," 

 Transactions of the Norfolk and Norwich Naturalists' Society, vol. v. 1890,pp. 144-156. 



