Laminaria saccharina and other Sea-Weeds. 263 



crystalline substance. Subsequently, in 1815, the L. saccha- 

 rina and five other fuci were again subjected to analysis by 

 M. Gaultier de Claubry, who also detected in the L. saccha- 

 rina and in the Halydris siliquosa the same saccharine sub- 

 stance, which he called manna. 



From the imperfect state of organic chemistry at these 

 early periods, neither of these eminent chemists were enabled 

 to subject this saccharine substance to analysis ; and so little 

 reliance has been placed upon their statements, that for some 

 years past they have been generally discredited both by che- 

 mists and botanists; Berzelius, for instance, has not once 

 mentioned sea-weeds as a source of mannite, though he has 

 enumerated all the other known sources ; and Dr. Greville, 

 in his Algm Britannica, regards the crystalline incrustations 

 which usually appear on the L. saccharina and the Halydris 

 siliquosa when dried, as nothing else than common salt. 

 Under these circumstances I was lately induced to subject the 

 Li. saccharina and some other sea-weeds to examination. 



A quantity of the dried L. saccharina was repeatedly di- 

 gested with hot water, which formed with it a mucilaginous 

 solution of a brownish red colour, and of a sweetish but at the 

 same time of a very disagreeable taste. When evaporated to 

 dryness 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 alcoholic 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, and possessing all the external 

 characters of mannite. When dried at 212° F., they were 

 subjected to analysis. 



I. 0'4<334< grm. of substance gave 0'6235 of carbonic acid 

 and 0-2995 of water. 



II. 0*4215 grm. gave 0*6058 carbonic acid and 0*294 water. 



Calculated Numbers. 

 At. Per cent. 



6 Carbon . 40*02 



7 Hydrogen 7*62 

 6 Oxygen . 52*36 



100*00 100*00 100*00 



It is evident from the result of these analyses, that the sweet 

 crystalline substance in the L. saccharina is nothing else than 

 mannite. The quantity of mannite contained in it is very consi- 



