418 Rk. H. Richards—Jet Aspirator for Laboratories. 
: Open 0; fill R, close it again. 
.; iH, 
3 Let on ue water ae which causes the mercury in 
ring the mercury in ‘B opposite to and on a level with 
that in G. This is done by raising the mercury with cock C, 
or by lowering it with cock C,, as the case may be. No 
the reading: call it r, 
(5.) Shut the water off and bring B and G again on a level, 
while C, is open for free admission of the atmosphere. Ta ke 
the reading and call it 
(6.) A barometer by the side of the air manometer will tell 
the number of mm. supported by the atmosphere: call it » and 
let m = the number of mm. of exhaustion shown by the air 
manometer; then by the law of ee tension we have—when the 
aspirator has produced a perfect vacuum— 
—Xn=mm. of mercury, able to balance the pressure of water. 
When the aspirator is open to the free admission of air— 
7 Xn n= mm. of mercury, as above. 
When the aspirator has produced a partial vacuum— 
= Xn— (am) = mm. of mercury, as above. 
These formule give the pressure of water which is actually 
called into use by the aspirator. 
In order to test the relative sizes of a and w as best suited 
for various columns of water, seven aspirators were made in 
glass, of varying dimensions, which are here shown 
Tas.e II. 
a. 0. Ratio’w*?:a?. Cone angle. 
Inches Inches. Inches. 
No. 1, 068 250 1:1 i? 
Wei 0612 075 240 1:14 “ 
aS 055 078 230 5 “ 
* 4, 052 090 "230 1:3 es 
ma OS "0425 085 250 1:4 °° 4 
Ree 0 090 270 1:5 «“ 
oe * 0635 246 ‘254 1:15 
The dimensions are all given in fractions of an inch, and [feel 
confident that the error does not exceed 002”. Thes e fine 
to measure a -and its exact point of pater ere bby the scratch 
of a file. The diameter of the cone at the pone Bi contact was 
