206 ANNUAL OF SCIENTIFIC DISCOVERY. 



without the immediate production of a precipitate ; if a solution of 

 urea be added to this mixture, the white precipitate of urea and pro- 

 toxide of mercury is immediately formed. This compound is so little 

 soluble in water, that by this process -g-^g-o urea can be detected with 

 certainty in a liquid. The whole of the urea can be precipitated 

 from urine by this means, and its application to the quantitative deter- 

 mination of urea in animal fluids is evident. Liebig. 



NEW ORGANIC BODY, PIIYCITE. 



The Academy of Sciences has received a memoir from M. Lamy, 

 upon a new substance he has succeeded in extracting from a sea-weed, 

 the protococcut vulgar is, or as it is commonly called in France, the 

 phyvie, a plant of very simple organization. Although this new sub- 

 stance, phycite, (as he calls it) is very sweet, M. Lamy objects to its 

 being called a sugar. There are in chemistry several sorts of sugars, 

 ' whose least important characteristic is their sweet savor. There are, 

 too, several sugared substances which are not real sugars. The cause 

 of this apparent contradiction, is in the necessity chemists lie under of 

 classing bodies rather according to their composition and the reactions 

 they furnish, than by the manner in which they affect our senses. 

 The first sugar studied was the common sugar, sold by every grocer. 

 This distinctly possesses but the sweet taste and the chemical and 

 physical qualities found in all bodies constituted after the same model. 

 It contains equivalent quantities of oxygen and hydrogen. It ferments 

 in contact with beer-yeast, and is transformed into alcohol and car- 

 bonic acid. Lastly, it acts in a well known and very remarkable way 

 upon polarized light. Other substances were subsequently examined, 

 and found to contain more or less sweet savor. Some of these fer- 

 mented, others did not; some active, others inactive on polarized light. 

 It became necessary to class them according to the relative importance 

 of these different characters, and at the risk of violating grammar, 

 chemists determined to class these bodies as if they had never tasted 

 them, and merely according to their physical and chemical affections. 

 By the side of cane sugar, grape sugar was next placed (though the 

 sweet flavor is much weaker than in the former,) then sugar of milk, 

 still less sugared, and lastly a certain unchrystallized sugar, which like 

 molasses, remains always more or less liquid. As to the sugar of man- 

 na, the sugar of liquorice, the sugar of gelatine and glycerine, which 

 do not ferment, and are without action on light, they have been struck 

 off the list of sugars, notwithstanding their greater or less sweet flavor. 

 It is upon these grounds M. Lamy declares phycite no sugar. Phycite 

 is especially remarkable for its tendency to chrystallize, (which is 

 always an index of a clearly denned composition,) the chrystals it fur- 

 nishes seem to belong to the system of right rectangular prisms. It is 

 distinguished from other sugars by the influence heat exerts on it ; 

 while real sugars are black and caramelized by the action of fire, phy- 

 cite, (although remarkably sweet,) is volatilized, and leaves in tho 

 capsule, where the experiment is made, nothing but some traces of 



