SLOT-XOZZLES 
199 
open or close the slot, or they may be entirely separable, better to enable 
cleaning and repairing. The part of the slot where the pressure or 
velocity is greatest, as where the injected stream strikes with the most 
force, should be narrowest, and rice versa, to get an evenly-distributed 
Bpray. Ill rotary slit-nozzles the width of the slot should increase some- 
what, but very slightly and gradually, in the direction of rotation, as 
along, triangular Harare. If the inverse is tried, particles flowing in 
the direction of the current naturally wedge fast between the lips, but 
with a gradual expansion in the direction of the movement the wedging 
along the slot cannot occur so often. 
In this class of nozzles, more than in any other, is the use of a .rotary 
body or projectile in the rotation chamber, and caused to whirl around 
by and with the fluid therein, of value for wiping away and keeping in 
motion or disintegrating internal foreign bodies tending to lodge upon 
and clog the excurrent orifice. A rotary brush or any tough body may 
be u>ed. A pebble, piece of stone, or very hard metal wears oil" the 
inner surface of the lips very rapidly, though this process goes slowly 
if the surfaces are or become very smooth; when a Iwxly is thus used 
the smoothing process progresses quite rapidly, as with metal castings 
put in a rattler. A pebble thus used soon becomes smoothly coated 
with tin' metal. Perhaps the best plan is to use a piece of material 
Softer than that of which the chamber is constructed. Compare Eddy- 
roses, p. 193. 
To be able to observe the internal whirling action the chamber was 
made with one face of glass. The whirling is exceedingly rapid, tend- 
ing to produce a vacuum, and certainly generating a raritication in the 
center which cannot be tilled witli liquid during the motion. This ceu- 
tral vacuity is quite large, and the water appears as a band around its 
outside. So rapidly does the fluid rotate under high pressure that 
bodies carried in ii are invisible. If a very small body be put in such 
a nozzle ami blown upon, it flies about invisibly fast and strikes so rap- 
idly as to make one continuous sound, but as you blow with gradually 
diminishing force the sound breaks into a series of rapid ticks, and by 
looking closely the little body may be observed flying around. 
The following are some of the nozzles which have been devised and 
perfected in my work under Professor Riley, whether for the Entomo- 
logical Commission or the Department: 
In Plate XVI, Fig. C, is seen a coarse, bevel-lipped side-slot, s, in the 
tubular part, <7, which bears a cap, c, with a beveled edge, which may be 
set so as to form a deflecting lip to the discharge, or to close it in part, 
or entirely. Thus is made an adjustable slot, and the cap may be re- 
moved, if necessary, for cleaning out. By different bevels, and by set- 
ting the cap farther on or off, the Spray can be deflected at a right 
angle, or iu planes at various other angles, which may be especially of 
advantage in spraying upward. 
In Plate XVI, Fig. 7, a similar nozzle is shown, differing chiefly in the 
use of a plug, o, in place of a cap, and having the deflecting rim oppo- 
