DYEING PROPERTIES OF WO AD. 423 



house in London, and received no less than 50 for his 

 parcel of gleaned seed. 



The dyeing properties of woad are due to a peculiar 

 vegetable product developed in the juices and cellular 

 tissues of the leaves during the fermentative process 

 through which it has to pass in its preparation for the 

 market. Upon the knowledge and skill of those employed 

 in this process of preparation the quality of the pro- 

 duct, and the consequent profit of the grower, mainly 

 depend ; for although the soil and season may be favour-- 

 able, and the yield great; the quality and market value 

 may be seriously affected by either want of knowledge or 

 of attention in the various stages of preparation through 

 which it has to pass. The various changes which the 

 woad undergoes in the process are all without doubt sus- 

 ceptible of a chemical explanation; but as the changes 

 in vegetable substances induced by fermentation are still 

 very imperfectly known, and as the investigations of 

 chemists in reference to such subjects have been directed 

 almost entirely to madder, we think it best not to attempt 

 any explanation of the process, but merely to describe 

 the modus operandi, so as to render the preparation 

 itself intelligible to those interested in the cultivation. 



A knowledge of the various indications by which any 

 opinion can be formed as to the progress of the operation 

 in its different stages, can only be acquired by experience 

 and careful observation in the houses where the woad is 

 prepared. The rules by which the process is regulated, 

 though entirely empirical, are still susceptible of a scien- 

 tific elucidation, consequently the process would be far more 

 readily comprehended, and far more likely to be improved 

 upon, by one who had previously made himself acquainted 

 with the principles upon which his manufacture was 

 based (the chemistry of fermentation'), than one who was 

 satisfied to continue working by the " rule of thumb." 



