3*8 



THE TROPICAL AGRICULTURIST. 



[October i, 1884. 



It will be seen that 90 per cent of all the salts are 

 thus removed, and much of those that remain are pro- 

 ducts of decomposition. These salts are obtained by the 

 carbonisation of the water extract, This is not necessary, 

 and may not be advisable, the salts can be fished out during 

 evaporation. I append analysis of a 2 cwt. sample so fished : — 

 Calcium sulphate ... ... 1"18 



Potassium sulphate .. ... 1.4*20 



Potassium chloride ... ..- 27*81 



Sodium chloride ... ... 55'11 



Sodium iodide ... ... ... 1*69 



99-99 

 Iodine 32 lb. to per ton. 

 Also of the mother liquor 54 ° Twad. evaporated — 

 Potassium sulphate ... ... 16'35 



Potassium chloride ... ... 17 1^ 



Sodium chloride ... ... 54*98 



Sodium carbonate ... ... 5*13 



Sodium iodide ... ... ... 5*27 



Water ... ... ... ... 70 



99*91 

 Iodine 100 lb. per ton. 

 We now come to the treatment of the residual weed. 

 If the long fronds of the -Laminaria Stenophylla be ob- 

 served after exposure to rain, a tumid appearance will be 

 noticed, and sacs of fluid are formed from the end osmosis 

 of the water through the membrane, dissolving a peculiar 

 glutinous principle. If the sacs be cut, a neutral glairy 

 colourless fluid escapes, It may often be seen partially 

 evaporated on the frond as a colourless jelly. This sub- 

 stance, which is then insoluble in water, is the remark- 

 able body to which I have given the name of Algin. The 

 natural liquid itself is miscible with water, but coagulated 

 by alcohol and by mineral acids. It contains calcium, 

 magnesium, and sodium, in combination with a new acid 

 which I call alginic acid. When this natural liquid is 

 evaporated to dryness, it becomes insoluble in water, but 

 it is very soluble in alkalies. This new substance is so 

 abundant in the plant that, on maceration for twenty- 

 four hours in sodium carbonate in the- cold, the plant is 

 completely disintegrated. The mass thus obtained is a 

 glutinous mass of great viscosity, and difficult to deal 

 with on that account. It consists of the cellulose of the 

 plant mixed with sodium alginate. The cells are so small 

 that they pass through many filters, but by cautiously 

 heating it. the mass can be filtered through a rough linen 

 filter bag, the - cellulose being left behind, and after the 

 algin is removed, this is easily pressed. 



The solution contains dextrine and other extractive 

 matter, and it is then precipitated by hydrochloric or 

 sulphuric acid; the algenic acid precipitates in light grey 

 albuminuous flocks, and is easily washed and pressed in 

 an ordinary wooden screw press. A filter press, made for 

 me by Messrs. Johnson and Company, answers perfectly 

 well for this operation, but not so well for the preceding. 

 It forms a compact cake, resembling new cheese, and has 

 only to be stored in an ordinary cool drying-room, where it 

 can be kept any length of time. If desired, by adding a 

 little bleach during the preciptuition, it can be obtained 

 perfectly white. The algin can be sent out in this state, 

 it is only necessary to dissolve it in sodium carbonate in 

 the cold for use. If, however, it be sent out as sodium 

 alginate, it must be dissolved to saturation in sodium 

 carbonate, the carbonic acid is disengnged. nnd sodium 

 alginate is formed. If potassium or ammonium carbonate 

 be used, the alginates of potassium or ammonium are formed, 

 which are similar to the soda-salt. The bi-carbonates of 

 these alkalies may also be used ; but the caustic alkalies 

 are not such good solvents. 



The sodium alginate forms a thick solution at 2 per 

 cent, it cannot be made above 5 per cent, and will not 

 pour at that strength. Its viscosity is extraordinary. It 

 was compared with well-boiled wheat starch, and with 

 gum arabic in an ordinary viscometer tube ; the strengths 

 employed were as follows; it was found impossible to 

 make the algin run at all over the strength employed: — 



Seconds. 

 Gum arabic solution, 2o per cent took 75=1 in 'A 

 Wheat starch „ 1-5 „ ,, 25=1 in S 



Algin „ 1-25 „ ,. 140=1 in 112 



So that the algm has 14 times the viscosity of starch, and 

 37 times that of gum arabic. 



I append analyses of two samples of commercial sodium 

 alginate of average composition • — 

 No. 1. 



P.O. ash 

 22-90 



P.C. ash 



22-575 



100-00 10000 



Dry algin ... 67'58 6550 



Soda (Na 2 O) 1071 1040 



Percent of Na 2 U 15-85 ■ 15-87 



Showing that, excluding the water, salts, and ash, the com- 

 position is uniform. 



The solution may be alkaline, or neutral, or acid, ac- 

 cording to the degree of saturation ; if alkaline, it may 

 be^ made distinctly acid by the addition of hydrochloric 

 acid, but any excess at once coagulates it; a 2 per cent 

 solution becomes semi-solid on this addition. 



The evaporation is effected in a similar manner to that 

 of gelatine, in thin layers on trays or slate shelves, in a 

 drying room with a current of air, or on revolving cylind- 

 ers heated internally by steam; high temperature 'must 

 be avoided. The solution keeps well. Thus obtained, the 

 sodium alginate presents the form of thin, almost colour- 

 less, sheets, resembling gelatine but very flexibe. It has 

 several remarkable properties which distinguish it from all 

 other known substances. 



Algin, or sodium alginate in solution is precipitated or 

 coagulated by alcohol, ethylic and methylic, acetone and 

 collodion (but not by ether) by acid hydrochloric, sulpho- 

 indigotic nitric, sulphuric sulphurous, phosphoric, citric, 

 tartaric, lactic oxalic and picric; salts of cobalt, copper, 

 platinum, nickel, silver, bismuth, antimony, zinc, cadmium, 

 aluminum, chromium, uranium, barium, calcium, strontium 

 ami tin chloride and bichloride ; mercury pernitrate and 

 protonitrate; iron sulphate (white) and iron perchloride 

 (brown); lead acetate and basic acetate; lime water and 

 baryta water. 



The solution is not precipitated nor coagulated by al- 

 kalies and salts of alkalies, including lithium, alkaline silicates, 

 potass bichromate (not coagulated hy boiling) and chrornate ; 

 sodium stannate, succinate, biborate and tungstate ; magnesi- 

 um and manganese salts, starch, glycerine, ether, cane sugar, 

 amylic alcohol, boracic acid, acetic', carbolic, tannic, butyric, 

 benzoic, gallic, pyrogallic, arsenious and succinic acids; 

 potass ferrocyanide, mercury iodide, ferricyauide and per- 

 manganate; bromine, iodine and chlorine water; molybd- 

 ate ammonia, tartar emetic and peroxide hydrogen. It 

 does not precipitate the ordinary alkaloids. 



It is distinguished from albumen, which it most resem- 

 bles, by not coagulating on heating and from gelose bv 

 not gelatinising on cooling, by containing nitrogen, and 

 by dissolving in weak alkaline solution, and being insolu- 

 ble in boiling water. 



From gelatine, by giving no reaction with tannin ; from 

 starch, by giving no colour with iodine, from dextrine, gum 

 arabic, tragacanth, and pectin, by its insolubility in dilute 

 alcohol and dilute mineral acids. 



It is remarkable that it precipitates the salts of the 

 alkaline earths, with the exception of magnesium, and 

 also most of the metals, but it gives no precipitate with 

 mercury bi-chloride nor potassium silicate. 



It has a strong rotary power on polarised light; Mr. 

 Tatlock estimated it for me as having a specific rotary 

 power of 86*5 ° on Laurent's polariscope. This again fixes 

 its position amongst animal bodies, gelatine, and albumen, and 

 notamongstsuch vegetable products as pectin, which isueutral. 

 Alginic acid is insoluble in cold water, very slightly in 

 boiling. It is insoluble in alcohol, ether, and glycerine. 

 The proportion of soda ash used is one-tenth of the weight 

 of the weed, and the cake of alginic acid obtained, is 

 usually about the same weight as the weed. The quantity 

 of dry alginic acid is given below : — 



Laminaria Digitata. 

 Stem. Frond. 



Water ... ... ... 37'04 440 



Alginic acid ... ... 21-00 17-35 



Cellulose ... ... 28-20 11-00 



