VOL. LV.3 PHILOSOPHICAL TRANSAfcTIONS. 241 



degrees of Fahrenheit's thermometer; which heat it endures for several hours, 

 before it is entirely detached from its union with them. It also appears, from 

 the above experiment, that in proportion as this mineral air is separated by lieat, 

 in the same proportion the more gross earthy parts of the water seem also to 

 separate from it; and that as the mineral air is thus entirely expelled, the water 

 is then wholly decomposed, its metalline and earthy particles having subsided, its 

 more volatile and elastic principles being exhaled, and nothing remaining in the 

 water, save only the small portion of alkaline and neutral salt, which is found 

 dissolved therein. 



It may here be noted, that the numerous analyses of these waters, which 

 have been attempted in retorts and receivers, where the water was exposed with 

 a large surface to the common air, the elastic substance seems to have been ex- 

 tracted from the water more readily, and with less heat than in the preceding 

 experiment; and pellicles have sometimes been observed on the water in the re- 

 tort, as on the same water exposed to the open air; the causes of which phe- 

 nomena will be explained hereafter. 



Exper. 3. In order to ascertain the quantity of air contained in the Pouhon 

 water, a Frontiniac phial was therewith tilled at the fountain, on a clear morn- 

 ing, when the wind was easterly, and a strong swine's bladder, well freed from 

 air, was immediately fitted thereto; all the air was then carefully expelled from 

 this water by the heat of the bath, after the manner related in the foregoing 

 experiment. The phial, with its contents, as soon as cold, was placed in an 

 inverted position, over a cistern of common water, so that the air, which had 

 been expelled from the water, ascended to the upper part of the phial, while an 

 equal bulk of the water contained in the phial descended into the bladder- 

 When all the air had ascended into the phial, the height at which the water 

 stood therein was marked with a diamond. The bladder being then removed, 

 the phial was carefully closed with a cork, and then taken from the cistern ; and 

 the air which it contained was kept therein, until it was wanted for the use 

 which will be mentioned hereafter. 



As soon as the phial was emptied of the air and water which it contained, and 

 had been exactly weighed, it was filled a second time with the Pouhon water, 

 which was found to weigh 20 oz. 7 dr. and 14grs. apothecaries' weight. The 

 phial was then emptied to the marks at which the water had stood therein, when 

 in an inverted position; and the water remaining in the phial (which now filled 

 the space that had before been occupied by the air extracted in the above-men- 

 tioned process) was found to weigh 8 oz. 2 dr. 50 grs. So that the bulk of the 

 air extracted from the Pouhon water was to the bulk of the water from which it 

 had been extracted, nearly as 8-|- to 20-J-. Or, if we choose to reduce the above 

 quantities into cubic inches, and allow a cubic inch of water to weigh 265 



VOL. XII. I I 



