( 449 j 
of the boring in the pump-body. This upper-end is provided with a 
very finely finished serew-thread in which the thread on the valve 
support fits very tightly (comp. § 2 9 2). The lower end of the 
boring in this steel support is turned out smooth and trumpet shaped, 
so that during compression bubbles of gas cannot remain behind 
(comp. § 2 D 2). The support fits on the pump body with the help 
of the enclosed washers eg. 
The conical part of the valve-pin ez) is ground with the utmost care 
on the support e3, when it is moved it is guided (comp. § 2 D 1) 
by a cylinder es. sliding up and down in the cylindrical opening es, , 
in which cylinder pieces are cut away along the lines of movement. 
The spring eys and the pin ej, prevent the lengthening piece egg 
from moving too much upwards. 
Moreover a slightly bent asbestos plate es, may be screwed in 
the valve between ¢3; and e33, which in some cases secures a better 
closure, but this means is not always applied. 
The upper part of the spray-catcher ej is supported by the 
cylinder e7;, screwed on to eg. The superabundant mercury pressed 
through the forcing-valve rises in this cylinder. The gas escapes 
through the openings e7;, and is directed downwards by the second 
cylinder ez; (comp. § 2 3 1). 
The plate ¢7; prevents the penetration of mercury into the upper 
part of the dome (comp. § 2 §. 1). After applying the second jacket 
no mercury drops were ever found on the plate. The outlet tubes 
es and eg for the gas from the head are, as in the case of CAILLETET's 
apparatus, provided at their upper extremities with flat ends in order to 
screw them on the washers in the bottom. The cock e,; through 
which we can allow the gas to flow out, without using the tubes e; 
and e,, is not now used because of the troublesome mercury-mist, 
which is produced on opening at high pressure. 
0. Exhaust-valve. (For the different sections and details of the 
valve-box and accessories see Pl. V fig. 1.) The steel valve- 
box f is fixed against the flat side of the pump body (comp. 
Pl. HD, in which the boring coincides with the boring f, in the 
valve-box. They are fastened together by bolts, running through 
the holes f, and screwed in the holes e, in the pump body. Be- 
tween the flat sides of the exhaust valve-box and of the pump-body 
india-rubber sheeting (45 mg. per cm*.) is laid over the grooves fy, 
which are useful in making a good closure. The support of the 
suction-valve fz is screwed in the piece f, while the closure takes 
place at the packing f;. The valve support is provided with nu- 
