178 



BULLETIN OF THE BUREAU OF FISHERIES. 



thus obtained has great viscosity, and is 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, Wut 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 dextrin and other extractive matter, and it is then precipitated by hydro- 

 chloric or sulphuric acid; the alginic acid precipitates in light gray albuminous flocks, and is easily 

 washed and pressed in an ordinary wooden screw press. It forms a compact cake, resembling new 

 cheese, and has only to be stored in an ordinary cool drying room, where it can he kept any length of 

 time. If desired, by adding a little bleach during the precipitation, 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 disengaged, and sodium alginate is formed. If potassium or 

 ammonium carbonate be used, the alginates of potassium or ammonium are formed, which are similar 

 lo the soda-salt. The bicarbonates of these alkalies may also lie used; but the 1 caustic alkalies are not 

 such good solvents. 



The sodium alginate forms a thick solution at 2 per cent: it can hot be made above 5 percent. 

 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: 

 Gum arabic solution, 25 per cent, took 7."> seconds=l in 3. 

 Wheat starch solution. 1.5 per cent, took 25 seconds=l in s. 

 Algin solution, 1.25 per cent, took 140 seconds = l in 112. 



So that algin has 14 times the viscosity of starch, and 37 times that of gum arabic. 



The solution may lie alkaline, or neutral, or acid, according to the degree of saturation; if alka- 

 line, it may lie made distinctly acid by the addition of hydrochloric acid, but any excess at once 

 coagulates it; a 2 per cent solution becomes semisolid on this addition. 



The evaporation is effected in a similar manner to that of gelatin, in thin layers on trays or slate 

 shelves, in a drying room with a current of air, or on revolving cylinders heated internally by steam; 

 high temperatures must be avoided. The solution keeps well. Thus obtained, the sodium alginate 

 presents the form of thin, almost colorless, sheets, resembling gelatin, but very flexible. It has 

 several remarkable properties which distinguish it from all other known substances. 



It is distinguished from albumen, which it most resembles, by not coagulating on heating, and 

 from gelose by not gelatinizing on cooling, by containing nitrogen and by dissolving in weak alkaline 

 solution, and being insoluble in boiling water; from gelatin, by giving no reaction with tannin; from 

 starch, by giving no color with iodine; from dextrin, 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 bichloride nor 

 potassium silicate. 



Alginic acid is insoluble in cold water, very slightly in boiling. It is insoluble in alcohol, ether, 

 and glycerin. 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: 



It is not necessary to extract the salts first with water ; it comes to the same thing to act on the 

 seaweed at once with soda ash, and to recover the salts by evaporation of the solution, after the alginic 

 acid has been precipitated. In this case chloride of calcium, or of aluminum, may be employed, the 



