AGRICULTURAL INDUSTRIES. 175 



size of billiard balls upwards, and in this shape the article appears 

 in domestic trade. This is indigo, with many impurities, as it is 

 universally used for blue dye. Ruri-kon, a dark indigo-brown, 

 inclining to violet or brown, is prepared from Ai with the addition 

 of lime and Aku, the ashes of indigo-refuse. Ten years ago, with 

 the aid of the government, attempts were made by means of sul- 

 phuric acid to separate indigo-blue from these Ai-tame (indigo- 

 balls), and to produce an exportable article. But they failed 

 because of the expense of the process. The most valuable Japanese 

 indigo is yielded by the province of Awa, in the island of Shikoku, 

 on the Linschoten Strait. 



In the year 1776 knotweed-indigo was introduced from China 

 into England, where dyers learned to use it under the name of 

 Persicaria. But its importation ceased later on when, owing to the 

 increasing cultivation of Indigofera Anil and other species, a better 

 article was furnished at reasonable prices from Bengal and Java. 



In 1826 Saint Hilaire, in France, directed attention to the 

 dyer's knotweed. Ten years later great numbers of these plants 

 were grown in the botanical gardens at Montpellier and Paris, 

 from which fresh material was obtained for the numerous experi- 

 ments undertaken between 1838 and 1840. Botanists, chemists, 

 agriculturists, and manufacturers emulated one another in study- 

 ing its properties.^ Their object was to test the plant and its 

 product for agriculture and dyeing. They hoped to introduce 

 into the country a new useful plant, through which its demand 

 for indigo might be supplied. This hope has not been fulfilled. 

 Of the prominent savans who took part at that time in this 

 indigo question, may be mentioned Saint Hilaire, Vilmorin, Delile, 

 Chevreul, Turpin, Joly, Baudrimont, Pelletier, and Robiquet. 



From the thorough treatise of our countryman. Dr. E. Schunk 

 of Manchester, already cited, I take finally the following memo- 

 randa on this subject : 



Schunk received from Paris some seeds of Polygomtm tinctorium, 

 which he sowed in a hot-bed, transplanting afterwards into soil in 

 the open air. Towards the end of summer he got beautiful pink 

 blossom-spikes, but no ripe seeds. When injured by insects or 

 otherwise, the pretty, bright, oval leaves did show blue spots, it is 

 true, but otherwise, even under the microscope, only chlorophyll, 

 and no other colour, was to be seen. 



A handful of leaves being chopped up and rubbed fine in a 

 mortar with a little water, and then pressed out, a green, slimy 

 fluid is produced, from which a green, flaky precipitate is separated 

 by a solution of acetate of lead. This precipitate consists of chlo- 

 rophyll, albumin, and other substances. The fluid thus filtered is 

 clear and yellow. On being mixed with hydrochloric or sulphuric 



^ See, among others, Turpin : " Etudes microscopiques sur le gisement de 

 la matiere bleue dans les feuilles du Polygonum tinctorium," etc. Comptes 

 Rendus VI L, pp. 806-S24 (1838). 



