BookVI. marine plants. 877 



fire extends over the whole floor of the kiln; the weed is then spread lightly on the top, 

 and added in successive portions. As it burns it leaves ashes, which accumulating 

 towards evening, become semifused, and are then well stirred. Another day's burning 

 increases the mass ; and this is continued till the kiln is nearly filled. On some occa- 

 sions the kiln consists of a cavity in the ground, over which bars of iron are placed ; and 

 on this the ware is burned, the ashes falling into the cavity, where they are well worked by 

 the proper instruments. 



5534. Kelp is generally divided into two kinds ; the cut- weed kelp, and the drift- weed 

 kelp ; the former made from the weed which has been recently cut from the rocks, the 

 latter from that which has been drifted ashore. The latter is supposed to yield a kelp of 

 inferior quality. Some specimens of kelp, however, made from sea-weed which had been 

 drifted asliore, tend to prove that this is not always the case. Weed which has been 

 exposed to rain during the process of drying, affords a kelp of inferior quality. It is 

 of the utmost importance to the manufacturer of kelp, to keep his weed as much as 

 possible free from rain. For this purpose many employ sheds ; when these are not at 

 hand, the weed which has been laid out to dry, should be collected into one heap during 

 the rain ; when this ceases, it should again be immediately spread out. It has often 

 been matter of dispute, how old the plants should be before they be cut. In general, 

 three years is the time allotted. This, however, from some trials which have been made to 

 ascertain this point, seems to be too long. From experiments, it appears, that the pro- 

 duce of kelp, from one ton of three years old weed, is only eight pounds more than that 

 from the same quantity of two years old ; from this we would conclude, that the weed 

 ought to be cut every two years. Though perhaps less weed may be procured from the 

 same extent of ground occupied by weed of two, than of three year's growth, yet the 

 difference may not be so great as to render it worth while to allow the weed to remain 

 for three years. 



5535. In order to increase the quantity of kelp, it has been suggested to the Highland 

 Society, that the seed of the salsola soda might be imported and cultivated at a small 

 distance from the shore, with the design of mixing the plant with the sea-ware, for the 

 improvement of the kelp. It was formerly imagined, that the barilla plant would not 

 produce any quantity of alkali, worth its cultivation, if planted in France ; but in the 

 year 1782, some spirited individuals procured a quantity of barilla seed, and made a 

 plantation of it near the coast of the Mediterranean, in the province of Languedoc, and 

 had the satisfaction for several years, to find, that the barilla which they produced from 

 these plants, was of a quality equal to that which they usually procured from Alicant. 

 Why, then, may not a similar attempt in our own country be equally successful ? 



5536. Other plants. If the growers of kelp could contrive to make some considerable 

 plantations of the most productive of the kali, or of fumitory, wormwood, and other 

 inland plants, which yield large quantities of potash, and collect the crop to burn with 

 the other materials, the carbonate of potash resulting from their incineration would 

 decompose the sea salt, and a great accumulation of carbonate of soda would be pro- 

 duced. It was proved long ago by Du Hamel, that the marine plants produced soda 

 merely in consequence of their situation, for, when they have been cultivated for some 

 years in an inland spot, they yield only potash. 



5537. There are immense tracts of shore on the mainland and islands of Scotland which may be 

 easily cultivated for the production of kelp, from which at present not one penny is derived. All the 

 cultivation requisite is, to place whin or other hard stones, not under the size of the crown of a hat, 

 upon such vacant spaces. Contracts have been made to plant shore lands in the Highlands with 

 such stones, at the rate of 20^. per Scots acre. Such stones are generally to be found at high-water 

 mark, on all the shores of the lochs of the Highlands. They are put into a boat at high water, 

 then carried to the ground to be planted, and thrown overboard, and on the ebb of the tide they are 

 distributed regularly over the shore, preserving a clear space round every stone of one foot, which 

 distance, after very minute examination, appears to be the most eligible for producing the greatest crop, 

 of ware. It is evident these stones should be of a round shape, the more surface being exposeil to the 

 alternate action of the air and water, so much more kelp-ware will be produced from a given space or 

 ground. In four years the first crop may be cut, which, on the above data, will yield about four per 

 cent, on the original expense. But the crop may be manufactured into kelp in every third year there- 

 after, which, on the same data, is equal to about five per cent. In this improvement'there is no hazard 

 of bad crops, and if the manufacture is begun early enough in the season, there is little danger to be 

 apprehended from bad weather, it being understood that tlie operation of kelp-making can be carried on. 

 should there be no more than two dry days in eight. {Highland Society's Trans, vol. viii.) 



Chap. X. 



Of Weeds or Plants which are injurious to those cultivated in Agriculture. 



5538. Every plant tvhich appears where it is not wanted may be considered injuriouSy 

 though some are much more so than others. A stalk of barley in a field of oats is a weed, 

 relatively to the latter crop, but a thistle is a weed in any crop j weeds, therefore, may be 

 classed as relative and absolute. 



