248 PHILOSOPHICAL TRANSACTIONS. fANNO l675. 



Exper. VI, On a proper quantity of clean filings of good copper, we poured 

 strong spirit of fermented, or rather putrified urine, to the height of an inch 

 above the copper ; and having let down a mercurial gauge, so that it leaned on 

 the bottom and side of the glass, we closed it very well with a stopple, and set 

 it in a quiet and lightsome place, noticing at what mark the quicksilver rested 

 in the open leg of the gauge. This done, suffering the menstruum to work 

 upon the filings, which it did rather slowly and very calmly without producing 

 any noise or sensible bubbles, it acquiring by degrees a very pleasant blue colour, 

 which by degrees grew fainter and fainter, till at the end of three or four days 

 the liquor was grown very pale. On taking out the stopple, that the air with- 

 out the glass might have access to that within, within four or five minutes, if 

 not less, the upper part of the liquor, that was contiguous to the air, had ac- 

 quired a fine blue colour, which descended deeper and deeper ; so that in less 

 than a quarter of an hour from the first unstopping of the phial, the liquor was 

 become throughout of a rich blue colour, and which in a few minutes longer 

 turned opaque. Carefully closing the phial again with the same stopple as be- 

 fore, the liquor began again, in two or three days, to lose of its colour. In most 

 of these experiments I forbore to shake the glass, lest it should be suspected, 

 that the agitation of the liquor might have raised some little fine powder, that 

 might have been supposed to have been precipitated from the tincture, and, 

 being thus mixed with the liquor again, restore it to its former colour. 



Exper. VII. On covering the bottom of a conical glass with a convenient 

 quantity of filings of good copper, we poured on them as much strong spirit of 

 sal ammoniac as served to swim about a finger's breadth above them ; and 

 having let down a mercurial gauge, and proceeded in all respects as in the fore- 

 going experiment ; without producing any noise or sensible bubbles, acquiring 

 by degrees a very pleasant blue colour, and afforded us also the phenomenon we 

 chiefly looked after ; which was, that for two or three days together the mer- 

 cury in the sealed leg of the gauge descended till it appeared to be near a quarter 

 of an inch lower than at first ; by which it appeared, that the spring of the air 

 contained in the cavity of the glass, and communicating with that in the open 

 leg of the gauge or syphon, was weakened in comparison of that in the closed leg. 



Exper. VIII. A mercurial gauge having been put into a conical glass whose 

 bottom was covered with beaten coral, some spirit of vinegar was poured in, 

 and then the glass stopple closing the neck exactly, on the working of the men- 

 struum on the coral, store of bubbles were for a good while produced, which 

 successively broke in the cavity of the vessel, and their accession compressed 

 the confined air, in the closed leg of the gauge three divisions, which I guessed 

 to amount to about the third part of the extent it had before : but some hours 



