Se ne oe ee 
— 
R. H. Richards—Jet Aspirator for Laboratories. 413 
In Ewbank’s Hydraulics I found quite a number of jet ar- 
rangements, none, however, which in any way touched the 
problem which was before me, i. e., to draw air by means of a 
pressure of water drawn from a hydrant. A jet pump was 
then made somewhat of the form presently to be described, but 
which received its water supply from the side tube 4, fig. 1, and 
w the air in through the central tube 1. 
With this form of aspirator the air was rarefied to about one- 
half its normal density, 880mm., but the instrument used an 
enormous quantity of water (and Boston water rates are high), 
and it was found to be a matter of the greatest nicety to adjust 
the tube 7 in order to obtain any aspiration at all. For these 
reasons, after a number of trials it was abandoned. 
ite a number of instruments were then made to ascertain 
duce the same result. The zig-zag bends now used were hit 
upon and proved entirely successful, and the form was so sim- 
eg that no further changes were sought. This form was per- 
ected during the winter of 1872-3 and was shown before the 
Society of Arts at Boston, in April, 1878. 
Since the middle of July, 1874, I have tried a number of ex- 
periments with a view to ascertain the best form of the aspira- 
tor'and also under what conditions it can be most successfully 
employed. : 
ere are several points which must be studied separately to 
produce a perfect instrument. If w=diameter of jet, fig. 3; 
a=diameter of the apex of the cone ao ; o=diameter of base 
of the cone and outlet tube; then the points for our considera- 
tion will be as follows: ae 
(1) The relative size of w and 0; (2) the relative proximity of 
a and w ; (8) the form and angle of the cone joining 4 and o ; 
(4) the relative sizes of a and w depending upon: 
(a) The amount of water column pressure; (6) the amount of 
rarefaction desired ; (c) the quantity of air d : - 
(1) The relative sizes of w and o.—As has been previously 
