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acid for aqueous vapour is equal to that of anhydrous space for the 

 same vapour at given temperatures. It has long been known that 

 concentrated sulphuric acid abstracts moisture from the atmosphere, 

 but the amount and the rate of this absorption have never been as- 

 certained with accuracy ; and consequently, in applying this acid to 

 purposes of exsiccation, the experimenter has often been at a loss to 

 know whether the acid vras sufficiently strong to render the space 

 in which it was confined perfectly anhydrous. By placing portions 

 of the acid, previously weighed, and diluted with known quantities 

 of water, under the receiver of an air-pump, with equal portions of 

 concentrated acid, of the specific gravity r8428, in similar dishes, 

 the author ascertained that the dilute acid could be concentrated to 

 the specific gravity 1*814, at a temperature varying from 65° to 

 57° : whence he concludes that acid of such strength is capable 

 of drying a vacuum when the temperature does not exceed 57°. By 

 making similar experiments in air, the author compared together the 

 weights lost by ten grains of dilute sulphuric acid of the specific 

 gravity 1'135, at three different periods of the day for six days, 

 taking note of the dew-point and the temperature ; and infers that 

 when the affinity of space for vapour, or the evaporating force, is 

 equal to 0'15 of an inch of mercury, it is just able to balance the 

 affinity for water of sulphuric acid of the specific gravity 1*249. 



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 offer 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 next. 



