3'4 



THE TROPICAL AGRICULTURIST, 



[October i, 18S4. 



of dulse, boiled in milk, the best of all vegetables. There 

 is no doubt that a valuable food is lost in entirely neglect- 

 ing the algae ; but I shall show, presently, how much of 

 this may be recovered in an available form. 



SEAWEED AS MANURE. 



This appears to me to be one of the worst applications 

 of seaweed, and I do no. think it has increased ; farmers 

 are beginning to find out that it seldom contains less than 

 80 per cent of water, often more ; and that for the actual 

 raauurial value in it, it may be very expensive if a long 

 cartage is required. Four tons of water, at least, must be 

 carte I for every ton of dry manure, and when dried there 

 is much additional expense, and it is very bulky. The 

 dry weed contains an average of 2 per cent of nitrogen, 

 so that, as it is used, it contains less than h per cent. 

 The chemical value is very little, except from the potash 

 contained ; but the mechanical value may be greater, as 

 in covering root crops as a protection from frost, or where 

 the soil is simply sand, and it binds it together. How- 

 ever, the cartage of water and the manufacture of soil 

 are expensive amusements, and seaweed is not much used 

 where there is high farming. It appears also, where con- 

 tinually used alone, to impoverish the soil ; it is like feed- 

 ing a dog on butter. The residue of seaweed ash, or kelp 

 waste, one ton of which is equal to forty tons of wet 

 seaweed, and contains all the phosphates, is quite un- 

 saleable for manure in this country. It may be remarked, 

 too. that in the wet climates of the west of Ireland, and of 

 Scotland, where it is mostly used, the application of water 

 is quite a superfluous operation for the farmer. 



Another application of seaweed, which I mentioned be- 

 fore, was the manufacture of paper. As far as 1 know, 

 this has only been carried out m France, on one plant, 

 the Zostera marina, or grass wrack, a material largely used 

 in this country for stuffing mattresses, and for packing 

 light furniture. Some curious specimens of this plant, 

 rolled up in little balls of fibre, were shown here at that 

 meeting, as thrown up by the sea at Majorca and Minorca; 

 and soon after it created a good deal of attention, having 

 been proposed as a substitute for cottou ; it contains litle 

 fibre, however. It grows in enormous fields, on sand-banks, 

 and is widely distributed, and is to be found in almost 

 every ocean ; it is a pure marine plant, with flowers, having 

 nothing in common with the alga? except the habitat. It 

 is often found on the shore perfectly bleached. All the 

 algae are cellular, and contain no fibre, but properly treated 

 they make a tough transparent paper, to which I shall 

 have to allude presently. 



THE MANUFACTURE OF KELP. 



This crude substance which, for many years, made the 

 Highland estates so very valuable, was at first made as 

 the principal source of carbonate of soda. At the begin- 

 ning of this century it realised £20 to £22 per ton, and 

 the Hebrides alone produced 20,000 tons per annum. The 

 importation of barilla then begau, and for the twenty-two 

 years ending 1822, the average price was £10 10s. The duty 

 was then taken off barilla, and the price of kelp fell to £8 

 10s. ; and in 1823, on the removal of the salt duty, it fell to 

 £3; and in 1831, to £2. It was used up to 1845 in the soap 

 and glass factories of Glasgow, for the soda. Large chem- 

 ical works were then existing in the island of Barra, built 

 by General McNeil], for the manufacture of soap from kelp, 

 and a very large sum of money was lost there. Two tall 

 octagonal chimneys were still standing not long ago, but 

 have now succumbed to the gales. In the meantime, soda 

 was being largely made by the Le Blanc process, and super- 

 seded kelp, which was always a most expensive source, 

 yielding only about 4 per cent, often less than 1 per cent; 

 it must have cost the soap-makers what would be equal to 

 £100 per ton for soda ash, the present price of which is £6. 



The manufacture of iodine and potash salts then began 

 to assume some importance, but the kelp required was not 

 the same; that which contained the most soda containing 

 the least iodine aud potash. Chloride of potassium, the 

 principal salt, was at onetime worth £25 per ton. The dis- 

 covery of the Stassfurt mineral speedily reduced this price 

 to about a third, and the further discovery of bromine 

 in this mineral, also reduced the price of that element 

 from 38s. peril), to Is. 3d., its present price. The amount 

 of bromine in kelp is small, about a tenth of the iodine, 

 and not now worth extracting. Large quantities are now 



produced in Germany and America. More recently, the 

 manufacture of iodine from the caliche in Peru has attained 

 large proportions, and has so far reduced the price of that 

 article, as to make its manufacture from kelp unremuuer- 

 ative. In a paper, compiled for the British Association, 

 published in 1877, 1 estimated the then total production 

 of iodine in Great Britain aud France, at 2,000 kegs of 

 1 cwt. each; and the future production of Peru at 6.000 

 kegs ; an estimate which is now being rapidly realised. 



In 1882, amount of iodine exported from Peru was 205,800 

 kilos., or 4,116 kegs, divided as follows:— 



To London ... 120,900 kilos. 



., Hamburg 62,100 „ 



„ New York 22,800 



205,800 „ 

 The present annual output is estimated at 300,000 kilos., 

 or 6,000 kegs. 



On the other hand, the present manufacture of Great 

 Britain and France is less than 1,000 kegs, the production 

 of France being now reduced to almost nothing, and the 

 kelp sold as manure. 



I append an abstract of a table in that paper, showing 

 the imports of kelp into Glasgow, to which city or its 

 district the manufacture of British iodine has always been 

 confined. 



The prices given are the average prices for the year ; 

 higher than the maximum, but not lower than the minim- 

 um, have been reached. It is remarkable that we are 

 now coming back to exactly the price of 1841, forty-three 

 years ago, and also exactly to the price of twenty-two 

 years ago, when my first paper was written. Potash salts, 

 however, were then three times the present price. 

 Imports of Kelp into Clyde. 

 Five years, 1841 to 1845. 



Tous of kelp, 1,887 in 1844 to 0,080 in 1845; average 

 3,133. Price of iodine per lb., 4s. 8d. in 1842 to bis. Id. 

 in 1845 ; average lis. 9d. 



Ten- years, 1846 to 1855. 

 Tons of kelp, 3,627 in 1846 to 11,421 in 1850; average 

 3,627. Price of iodine per lb., Ss. 8d. in 1851 to 21s. 3d. 

 in 1S46; average 12s. lid. 



Ten years, 1855 to 1865. 

 Tons of kelp, 6,349 in 1856 to 14,028 in 1863; average 

 9,730. Price of iodine per lb., 5s. in 1863 to 13s 8d in 

 1856; average 8s. 10s. 



Ten years, 1866 to 1S75. 

 Tons of kelp, 8,116 in 1868 to 10,923 in 1874; average 

 9,187. Price of iodine per lb., 10s. in 1866 to 34s. in 1872; 

 average 15s. lid. 



Seven years, 1870 to 1883. 



Tons of kelp, about 6,000 to 8,000 ; average about 7,000 

 Price of iodine, 5s. in 1883 to 15s. 6d. in 1S79; average 

 about 10s. 2d. 



Total average kelp import, 1841 to 1883 (42 years) 6,750 

 tons. Average price of iodine per lb., 12s. 



So that the present price is only about 40 per cent of 

 the average value. The great fluctuation in the price, and 

 the small bulk of the article in proportion to its value 

 and the limited production, have led to great speculation' 

 and I have no doubt a few kegs might still be found here' 

 and there in London which were bought some years ago 

 at a pretty high price, and are still waiting the improb- 

 ability of a turn in the market. 



The amount of iodine in seawater is so miuute, that 

 it is extremely difficult to detect by ordinary tests ; by 

 evaporating down two portions of seawater filtered and 

 unfiltered, each over 14 gallons, and by employing a delic- 

 ate colour test, I have succeeded in estimating it. The 

 seawater was collected carefully in the Atlantic, west of 

 the island of Tyree. I found in 1,000,000 grs. measure 

 (14-2857 gallons) of unfiltered seawater, '003572 or 1 in 

 280,000,000; in 1 ,000,000 grs. measure of filtered seawater 

 ■003442 or 1 in 291,000,000. The unfiltered water might be 

 expected to contaiu more iodine from minute alga? in 

 suspension, although it appealed clear. Kortstoffer, who 

 estimated it in the Mediterranean, puts it at 1 part in 

 50,000,000. Bromine is easily detected ; sea water gener- 

 ally contains about 6 parts in 100,000, aud of chlorine 



