SANTALIN — SILICA 361 



or thin plates. It is colored by concentrated sulphuric acid, 

 and, on the addition of a little water, a red powder is thrown 

 down in the sulphuric acid solution. 



Santalin. — Santalin is the coloring matter of the red sandal- 

 wood, Pterocarpus santalinus. It is insoluble in water, but is 

 soluble in ether with a yellow color, and with 80 per cent, alcohol 

 it gives a blood-red solution. Stronger alcohols give the same 

 result. It is also soluble in acetic acid and in aqueous alkaline 

 solutions. 



Saponin, CjgHgjO,,. — This glucoside occurs in solution in 

 the cell-sap of many Leguminosse. Quillaja saponaria con- 

 tains in the bark 2 per cent, of saponin. It is easily soluble in 

 water and is precipitated from solution by the addition of strong 

 alcohol. When treated with a mixture of equal parts of alcohol 

 and sulphuric acid, a yellow color is produced which soon 

 changes to red, and later to violet. If it is then treated with 

 a concentrated solution of chloride of iron, a brown or bluish- 

 brown precipitate is formed, the intensity of the bluish color 

 increasing with the amount of saponin present. 



Seminose. — Seminose is one of the products resulting from 

 the hydrolysis of hemicellulose by sulphuric acid. It is dex- 

 trorotary, reduces Fehling's solution, and is fermentable. 



Silica, SiOj. — Silica occurs in the skeletons of diatoms, and 

 as incrustations over the epidermis of the Equisetaceae and 

 Gramineae. It also sometimes occurs in masses in the interior 

 of cells. It may be isolated from the organic matter with which 

 it is associated by burning over a flame bits of epidermis incrusted 

 by it, or diatoms, which are placed in a drop of concentrated 

 sulphuric acid on a piece of platinum foil. By this treatment 

 the organic matter will be destroyed, and the silica will remain 

 behind as a pure white ash. The silica may also be obtained pure 

 by placing bits of tissues incrusted by it in a drop of concentrated 

 sulphuric acid, and then after a time adding 20 per cent, chromic 

 acid, and following this with additions of still stronger chromic 

 acid until a considerable strength has been reached, and, finally, 

 washing in water and alcohol. Silica is distinguished by being 



