j 44 Observations en

of the carriage had contributed to it; for,except in those circumstances, I never foundany of it. At one time I found, after re-moving my quicksilver, which was abouttwelve pounds, from London into thecountry, there was r^ear a pound of thisblack powder on the surface of it. This Ithought a great acquisition, as it was aquantity sufficient for a variety of experi-ments.

The first thing that occurred to me todo with it was to endeavour to expel airfrom it by means of heat. Accordingly, Iput a quantity of it into a glass phial witha ground stopper and tube, and, with theheat of a candle, I presently expelled fromit a quantity of air ; which being admittedto lime water made it very turbid, and was,in a great measure, absorbed ; a proof thatthe air it had contained was in part fixedair, and the remainder was not so muchdiminished by nitrous air as common airwould have been ; so that no pure air camefrom this black powder, and consequentlyit differed essentially from the -precipitate

per