374 M. de Saint Giles on Hydrated Sesquioxide of Iron. 



polarizatiou to the right ; it has the formula of grape-sugar, is 

 unfermentescible, aud agrees in most of its properties with sorbine. 

 The formation of eucalyne may be thus expressed : — 



Melitose. Eucalyne. 



Melitose appears, then, to be formed of two isomeric compounds, 

 of which one is fermentescible. The action of j^east disunites 

 them, destroying the one without attacking the other. 



M. Berthelot points out, from the similarity in the properties 

 of this body to cane-sugar, the probability that this analogy ex- 

 tends to the constitution of cane-sugar. This, he observes, has 

 been rendered probable by the researches of M. Dubruufaut. 



M. Berthelot has ascertained the existence, in the Pimis Lam- 

 bertianus, of a crystallizable saccharine principle. Finite, which is 

 isomeric with quercite, and hence differs from maunite by the 

 elements of water. From its reactions it may be ranged along 

 with this class of substances. It forms with stearic and benzoic 

 acids peculiar compounds, with the study of which the author is 

 engaged. 



By heating the hydrated sesquioxide of iron, Fe^ O^(HO)'*, to 

 100 C. it loses one- third of the water. M. de Saint Giles finds 

 that if this heating be prolonged some time, the change does 

 not merely consist in a loss of water, but that the properties 

 of the hydrate are considerably modified. Its colour is changed, 

 it resembles the calcined oxide in appearance, and it has lost 

 to a great extent its basic properties. It is much less easily 

 soluble in acids, and does not produce prussian blue with ferro- 

 cyanide of potassium. It no longer exhibits the phsenomena of 

 incandescence on being heated to a dull redness, which is cha- 

 racteristic of the non-modified hydrate. He has also found that 

 acetate of peroxide of iron undergoes, when heated, a similar 

 change. Instead of water, acetic acid is liberated. 



The natural ferric hydrates are divided into two classes, which 

 correspond with these two states. Those of the first species are 

 crystalline, and have the colour of the calcined or of the modified 

 hydrate. They contain 10 per cent, of water, which corresponds 

 to Fe- 0^, HO. The second species contains the amorphous 

 hydrates : they have a yellowish-ochreous colour, and their for- 

 mula is Fe^O^(HO)'i, agreeing with the non-modified hydrate. 



M. de Saint Giles thinks that in the modified hydrate a true 

 allotropic transformation has been effected, and he points out 

 that the changes which Crum has observed in the acetate of alu- 

 mina are perfectly analogous. He has confirmed the observa- 

 tions of Crum, and has also found that the hydrate of alumina is 

 modified by heating in a similar manner. 



