THE USES OF SEA-WEEDS. 69 



my friend Dr. John Stenhouse has detected in many of our 

 coarse Sea-weeds, but in greatest abundance in Laminaria 

 saccharina, which we doubt not took its specific name from 

 this circumstance. A quantity of this Sea-weed was by 

 Dr. Stenhouse repeatedly digested with hot water, which 

 formed with it a brownish, sweetish, mucilaginous solution. 

 When evaporated to di-yness on the water-bath, it left a 

 considerable quantity of a saline semi-crystalline mass ; this 

 was reduced to powder and treated with boiling alcohol, by 

 which a considerable portion of it was dissolved. The 

 alcholic solution, on cooling, became nearly solid from the 

 quantity of long transparent prismatic crystals with which 

 it was filled. When purified by a second crystallization 

 these were deposited in large hard prisms of a fine silky 

 lustre. By analysis it was found that this was Mannite. 

 The quantity of Mannite contained is very considerable : 

 one thousand grains of the Sea-weed treated in the way 

 described gave about 12 per cent, of Mannite. It is very 

 beautiful — as purely white as loaf-sugar, and almost as 

 sweet. Since I wrote the above I have examined and tasted 

 Mannite which T got from Dr. Stenhouse about four years 

 ago, and it is as white and sweet as ever. Surely some use 

 may be made of this sweet marine treasure. No doubt it has 



