( 447 ) 
The T-piece do, (Pl. VI fig. 1) is screwed on the two tubes d, 
and d3, so that the bend of the former becomes of the required 
form, the proper thickness is then given to the leather packings 
dy, and dg, the closure being obtained by securing nuts dy, and do. 
The passage for the mercury, is interrupted in the T-piece by 
two bends daj, and dg 9, opening into a space dg 3, which space is 
closed by a tap provided with packing d,3 and also with an opening 
with its screw d,, and accompanying packing. 
It is used. during the cleaning of the pump to run off mercury, 
for which purpose the T-piece is held downwards; moreover drops 
of glycerine if they are carried along by the mercury can gather 
in dg and be drawn off through day. It is seldom necessary to 
dismount the double bent tube. A great convenience of the above 
mentioned arrangements is that the mercury can always remain 
in the pump and hence the introduction of dust or splinters is not 
to be feared. 
e. The pump body e with its water circulation eg (Pl. Ill and V) 
is in the main the same as CaILLeTrT’s. Here also the head e, is 
hermetically fitted on the pump body by means of a leather ring 
while a layer of mercury renders the closure of this packing perfect 1). 
The iron basin e; is arranged to prevent the mercury being spilt 2). 
c. Connection of pump-cylinder and pressure-reservoir. The steel 
capillary < is fixed at both ends in the cocks 4 and ig. The latter 
is adjusted at the height of the suction-valve. At first the commu- 
nication was made for convenience along d,, but it is evident that 
the leaking of gas into the pump-cylinder, whenever the cock is 
not shut in time, may cause great inconvenience. 
The cocks # í are constructed according to the Leiden model of 
high pressure cocks. In order that they should work satisfactorily it 
is most important that everything should be very accurately prepared 
on the lathe, so that the point of the pin #39, which is hardened, 
fits quite centrally into the conical hole #%). When the pivot is 
loosened, the gas must be able to move freely along #33, and there- 
fore the space left should not be too small. The serew-thread #32 
must not cut the packing when the cock is entirely open, and hence 
the pivot #33 must have the full thickness out of which the screw is 
1) The packing is tightened by means of a key with a very long handle. 
2) The floor in the neighbourhood of the pump is arranged so that any mercury 
spilt can be easily collected, 
