Figure, 'mercurial vacuum tap' by J T [James Thomson] Bottomley A drawing of Bottomley's mercurial vacuum tap, with parts labelled A-F and p. 'The tap consists of three parts. AB is a tube containing a glass float, of which the upper end is conical, and ground very carefully at aa to fit a conical opening to the upgoing spirit-bore tube AM; and at M the apparatus which is to be exhausted would be blown on. At C there is an ordinary cup and stopper, ground to a very perfect fit,and the joint at C is made perfectly air-tight in the usual way by pouring mercury into the cup. At the lower extremity of the part CD is a stopper closed at the bottom, but with a fine hole drilled at p; and in the tube of the cup EE there is a fine groove cut, which reaches half way up the ground part of the tube and stopper to p; but above p there is a sufficient length of grinding to make a perfect joint. When the hole p is turned round to meet the groove, there is communication through and through the tap, that is to say, from the pump below F to the apparatus attached to M; but when the opening p is turned away from the groove the pump is cut off. Subject: Scientific apparatus and equipment A print of this figure was published in volume 40 of the Proceedings of the Royal Society alongside the paper 'On an apparatus for connecting and disconnecting a receiver under exhaustion by a mercurial pump'. 1886