Intelliaence and Miscellaneous Articles. 467 



*fc> 



The author next instituted a series of experiments to ascertain 

 whether the evaporation of water from dilute sulphuric acid is capa- 

 ble of being carried on to the same extent in air as in vacuo, and 

 found that the evaporating force of air exerted upon such acid is less 

 than that of a vacuum at the same temperature. He observes that 

 his experiments oiFer conclusive evidence that the evaporation of 

 water is not owing to the existence of a chemical affinity between 

 the vapour of the liquid and atmospheric air ; but thinks that they 

 favour the notion that the obstruction to this process in the open 

 atmosphere is rather owing to the pressure than to the vis inertia 

 of the particles of air. He is also of opinion that improvements will 

 hereafter arise from this inquiry with regard to the economical 

 management of the process of manufacturing sulphuric acid, which 

 process would be greatly expedited by the regulated admission of 

 steam into the condensing chambers kept at a constant high tem- 

 perature. 



The Society then adjourned over the long vacation to meet again 

 on the 15th of November. 



LXVI. Intelligence and Miscellaneous Articles. 



XYLOIDINE. 



THIS name was given by M. Braconnot to a substance produced by 

 the action of concentrated nitric acid upon starch and lignin; the 

 composition of this substance, and of others which accompany its 

 formation have not been examined ; and its principal properties have 

 been either imperfectly described or quite unknown. M. Pelouze 

 has lately undertaken the investigation of its properties, and the prin-> 

 cipal results of his experiments are the following : 



If a mixture of starch and nitric acid of sp. gr. 1*5 be made, the 

 starch entirely disappears in a few minutes ; the liquor preserves the 

 yellow tint of the concentrated nitric acid, and no elastic fluid is 

 evolved : when immediately treated with water the xyloidine is en- 

 tirely precipitated, and the filtered liquor when evaporated yields a 

 scarcely perceptible residue. 



If instead of effecting the precipitation by water, immediately 

 after the solution of the starch, the solution is allowed to remain in 

 a close vessel, it becomes gradually coloured, and assumes the various 

 tints of a mixture of nitric acid and nitric oxide. Water then forms a 

 precipitate of xyloidine, the quantity of which diminishes with time ; 

 after two days, and sometimes even after some hours have elapsed, 

 water ceases to render it turbid : the xyloidine is destroyed and com- 

 pletely converted into a new acid, which is by evaporation procured 

 in the form of a white, solid, uncrystallizable, deliquescent mass, 

 the weight of which is much greater than that of the starch submitted 

 to experiment ; but neither carbonic acid nor oxalic acid is produced 

 during this reaction. 



The xyloidine, the first product of nitric acid upon starch, results 

 from the combination of these two bodies ; it is common starch con- 

 taining an atom of water, which is replaced by an atom of nitric acid. 

 The starch is entirely converted into this substance ; and this per- 



2H2 



