1911 Encyclopædia Britannica/Sunn
SUNN, or India Hemp (Crotalaria juncea), a plant which is a native of India and Ceylon. It frequently receives other names, e.g. false hemp, brown hemp, Bombay hemp, Jubbulpore hemp, sana, &c. The plant is an annual, requires a light soil, and is easily cultivated. The ground is ploughed two or three times, and from 80 to 100 ℔ of seed are sown broadcast. The seedlings quickly appear above the surface, but it is about four months before the plant begins to flower. Sometimes the seed is sown in October for the winter crop, and sometimes in May or June for the summer crop. When the seeds are sown in May, the bright yellow flowers appear in August, when the plant may be gathered. It is not unusual, however, to defer this operation until the seed is ripe, especially if a fibre of great strength is desired. The stems may be pulled up, as is the case with flax, or they may be cut down. Different opinions exist as to whether the stems should be steeped immediately after they are pulled, or left to dry and then steeped: in the wet districts they are taken direct to the water. Since the root ends are much thicker and coarser than the tops, it is common to place the bundles erect, and to immerse the root ends in about a foot of water. Afterwards the bundles are totally immersed in the ponds, and in two to four days the fibre should be ready for stripping. There is the same danger of over-retting and under-retting as in other fibres, but when the retting is complete, the workmen enter the ponds, take up a handful of stems, and swish them upon the surface of the water until the fibre becomes loose. After the fibre has been peeled off it is hung over poles to dry. When intended for cloth it is combed in order to remove any foreign matter, but if it is intended to be used for rope or similar purposes, the fibres are simply separated and the woody matter combed out with the fingers. The fibre is of a light grey colour, and has an average length of 3 to 4 ft. It is extensively used for rope and cordage and also for paper-making in its native country, but it has made little, if any, progress in this country. According to Warden, the fibre was tried in Dundee in the beginning of the 19th century. About 1820 the price of India hemp bagging, as quoted in the Dundee Advertiser, was 1½d. per yard below hemp bagging, and ¾d. a yard below tow warp bagging.
It is stated in Sir G. Watt's Dictionary of the Economic Products of India that a cord 8 in. in size of best Petersburg hemp broke with 14 tons, 8 cwt. 1 qr., while a similar rope of sunn only gave way with 15 tons, 7 cwt. 1 qr. Roxburgh's experiments with ropes made from this and other fibres appear on p. 607 of the above work. The ropes were tested in the fresh state, and also after having been immersed in water for 110 days. His results, reproduced in the following table, show the comparison.
| Names of the Plants. | Average Weight at which each sort of line broke. | ||||||||
| When fresh. | After 110 days' maceration. | ||||||||
| White. | Tanned. | Tarred. | White. | Tanned. | Tarred. | ||||
| English hemp, a piece of new tiller-rope |
|
— | — | Rotten, as was also the English log-line. | |||||
| Hemp from the East India Company's farm near Calcutta |
|
139 | 45 | All rotten. | |||||
| Sunn hemp of the Bengalese |
|
69 | 60 | Rotten | 51 | 65 | |||
| Jute (Bunghi-pāt) | 68 | 69 | 61 | 40 | 49 | 60 | |||
It would appear that, after maceration, neither ordinary hemp nor sunn hemp can compare with jute for strength.