374 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



in water, is the remarkable body to which is given the name of algin. The natural 

 liquid itself is miscible with water, but is coagulated by alcohol and by mineral acids. 

 It contains calcium, magnesium, and sodium, in combination with a new acid, called 

 alginic acid. When this natural liquid is evaporated to dryness it becomes insoluble 

 in water, but is very soluble in alkalies. 



This new substance is so abundant in the plant that on maceration lor 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 precip- 

 itated by hydrocloric 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 be 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 to the soda salt. 

 The bicarbonates of these alkalis may also be used, but the caustic alkalis are not 

 such good solvents. 



The sodium alginate forms a thick solution at 2 per cent; it can not be made over 

 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 viscom- 

 eter 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, 25 per ceut, took 75 1 in 3 



Wheat starch solution, 1*5 per cent, took 25 1 in X 



Algin solution, 1'25 per cent, took 140 1 in 112 



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



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 temperature must be avoided. The 

 solution keeps well. Thus obtained, sodium alginate presents the form of thin, 

 almost colorless sheets resembling gelatin, but very flexible. These sheets can be 

 written upon or printed. It is said that in some parts of Japan this substance, which 

 is translucent, has been used instead of glass to admit light to the dwellings of the 

 pooier classes. 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 gelatinating on cooling; from 

 gelatin by giving no reaction with tannin ; from starch, by giving no color with iodine; 

 from dextrin, gum arabic, pectin, and tragacanth, by its insolubility in dilute alcohol 

 and dilute mineral acids. 





