DIATOMS 9 



cus Ehrenbergii, being especially characteristic and are disk-shaped, 

 from 0.100 to 0.200 mm. in diameter. Through this mucilaginous 

 matrix there are small swollen aggregates of starch grains of some of 

 the Floridese. In poorer specimens of Agar-agar the fragments of 

 diatoms and spicules of sponges are rather numerous. 



Powder. Pale buff in color and consisting of angular fragments 

 which when mounted in water are transparent, more or less granular 

 and striated. It also shows masses of swollen starch grains, frus- 

 tules of diatoms, and spiculse of sponges mentioned above. 



Constituents. About 65 per cent of a mucilaginous substance 

 (Gelose) yielding galactose on hydrolysis and mucic acid on ox- 

 idation; about 6 per cent of nitrogen-containing substances; 3.5 

 per cent of cellulose; not more than 5 per cent of ash; and about 22 

 per cent of water. 



Agar-agar is insoluble in cold water, but if 1 part of Agar-agar be 

 boiled for about ten minutes with 100 parts of water it yields a stiff 

 jelly upon cooling. A solution made by boiling 0.100 gm. of Agar- 

 agar in 100 c.c. of water, upon cooling should not yield a precipitate 

 with a solution of tannic acid (absence of gelatin), and not give more 

 than a slightly reddish or reddish-violet color upon the addition of an 

 iodin solution. 



Literature. Tschirch, Handbuch der Pharmakognosie ; Takao, 

 Jour. Pharm. Chim. 1917, 15, p. 175. 



BACILLARIACE.E, OR DIATOMS 



TERRA SILICE A. Siliceous Earth, Kieselguhr, Infusorial Earth. 

 This occurs in natural deposits which are mined and usually calcined 

 to destroy the organic matter, after which it is washed and dried. 

 The article used in pharmacy is further purified by boiling with 

 diluted hydrochloric acid, washing and calcining, and is known as 

 Terra Silicea Purificata. 



Description. Purified siliceous earth is a very light and fine 

 powder, odorless, and of an oyster-white color. It is insoluble in 

 water, and upon boiling with distilled water and filtering, the filtrate 

 should be colorless and neutral to litmus paper. It should be prac- 

 tically free from any carbonates or sulphates and contain not more 

 than a trace of iron. 



Inner Structure. While siliceous earth consists almost entirely 

 of the frustules of diatoms yet they may be variously preserved in 

 different samples. In some specimens a large number of nearly per- 

 fect forms may be discerned, whereas in others they are for the most 

 part broken up. It will be interesting to determine the relative 



