Ron sett aie See ei Fs me oe rene, Mente ery summerantmnn inca i 
Ber 
erated 
2% 
‘ena 
R. H. Richards—Jet Aspirator for Laboratories. 419 
measured by the gauge. ‘To obtain the jet w, a having already 
been measured, let <== the ratio which we desire to fulfil, 
a? : ; 
then JF=ine diameter of w which we require. Another 
acute glass cone is cut off at the right diameter by means of 
the gauge and a file, and the apex half of this cone is dropped, 
downward, into the already formed jet (fig. 13), which is 
then cut off exactly at the base of the cone. The greatest 
source of error lies in the fact that the steadiest hand cannot 
always rely upon making the cross section of his jets true math- 
ematical circles. 
Explanation of letters, terms, etc., used in the following experiments. 
G, isthe column recording the gauge readings under the at- 
mospheric pressure alone. 
G, is ditto when the water has been turned on and the aspira- 
tor has attained its greatest vacuum. 
G, is the column recording gauge readings taken just after G, 
and with only one change in the apparatus, 1. e., the air is 
freely admitted to the aspirator, the water cock remaining 
untouched. 
H, A and H-A are the air manometer readings, the latter giv- 
ing the number of mm. sustained by the difference in ten- 
sion between the normal and the exhausted air. 
In each case below will be found a calculated statement of 
the actual water pressure which was used to sustain the (H-h) 
of the atmosphere, which is placed next to it on the same line. 
One pair of columns is marked “with vacuum,” the other 
“without vacuum ;” in the first of these the water pressure is 
calculated from G, and G 
B xn—(n—m)=E! xn— 4 n—(H—A) }. 
2 
Tn the second it is calculated from G, and G,. 
winds ui ies 
rs xn G, Gf mee ( 
The exact cause of the difference of readings G, and G, is 
worthy of note. The reading G, is taken when the water cock 
1s in exactly the same position as when G, was read, but the 
atmosphere has been admitted to the chamber c and the addi- 
tional impelling force to the water which lowered G, is now 
Wanting and hence the gauge rises when G, is taken. The 
question may be asked, “ what right have we to charge to one 
experiment a different amount of pressure from what we do to 
another when the gauge in both cases reads the same, or, as some- 
