4 U. S. BUREAU OF FISHERIES. 



The preparation of agar involves quite a number of steps, but 

 on the whole is a simple process: (1) The seaweeds are collected 

 by hand or rakes ahd spread upon the beach to dry and bleach in 

 the sun. (2) The dry weed is beaten or pounded by hand or passed 

 through a concrete mortar-and-pestle battery to free it from cling- 

 ing shells, incrusting Bryozoa, sand, and other foreign matter, and 

 is then alternately washed and sundried again until thoroughly 

 bleached and cleaned. This treatment requires from tw^o to several 

 days. Some manufacturers are said to shorten the process by bleach- 

 ing with chemicals instead of sunlight. (3) The bleached raw ma- 

 terial is boiled with about 50 times its weight of water in an iron 

 kettle for three to five hours to extract the gelose in soluble form. 

 The solution is then separated from the insoluble matter by filtering 

 the mass first through coarse cloths and then squeezing it through 

 linen bags in a press. (4) The filtered jelly is next poured into 

 wooden trays about 2 feet long, 1 foot wide, -and 3 inches deep to 

 cool. As the filtrate cools it solidifies into a hard jelly which the 

 Japanese call "tokoroten." In this form it is cut by means of 

 sharp knives into blocks 1 foot long and 2 inches square. These 

 blocks are in turn pressed through a coarse wire grating which cuts 

 them into bundles of slender straws. (5) In this condition the 

 "tokoroten" is subjected to a freezing temperature of —5° to 15° C, 

 either out of doors or in an artificial freezer, until the sticks are 

 frozen solid. This causes the water to crystallize out and when it 

 is melted the substances soluble in cold water drain off in solution 

 leaving the gelose in pure condition. By repeating the freezing 

 and thawing process and at the same time drying the material in the 

 sun and open air a pure agar which is insoluble in cold water is pre- 

 pared. (6) Before the sticks are entirely dry they are sometimes 

 put through a forcing machine which flattens each fine strip into a 

 transparent sheet. They are then dried in the sun and tied in bun- 

 dles weighing from | to 3 pounds each. 



Agar-agar is prepared also in the form of sheets 8 to 12 inches 

 long and 1 to 1^ inches wide, and as rectangular blocks about 8 inches 

 long and 1 inch square. 



The chemical composition of agar-agar has been most carefully 

 studied by Carl R. Fellers, whose results are published in the Jour- 

 nal of Industrial and Engineering Chemistry, volume 8, No. 12, 

 1916, pages 1128-1133. Analyses of 15 samples collected from various 

 sources and representing different brands gave the following results : 



Per cent. 

 Moisture 15. 75-17. 84 



Protein (N x 6.25) 1. 03- 2.04 



Nitrofxon free extract 72. 72-78. 21 



Ethor extract .17- .45 



Crude fiber .89-1.60 



Ash 3.08- 5.68 



Silicon dioxide . 31- 1. 11 



