SLOT-NOZZLES 199 



Open or close the slot, or tliey may be entirely separable, better to enable 

 cleaning and repairing. The part of the slot where the pressnre or 

 Velocitj' is greatest, iis where the injected stream strikes with the most 

 force, should be narrowest, and vice versa, to get an evenly-distributed 

 spray. In rotary slit-nozzles the width of the slot should increase some- 

 what, but very slight! 3^ and gradually, in the direction of rotation, as 

 a long, triangular fissure. 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 used. A pebble, piece of stone, or very hard metal wears off" the 

 inner surface of the lips very rapidly, though this process goes slowly 

 if the surfaces are or become very smooth -, when a body 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 the 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 v.ith one face' of glass. The whirling is exceedingly rapid, tend- 

 ing to produce a vacuum, and certainly generating a rarification in the 

 center which cajmot be filled with liquid during the motion. This cen- 

 tral vacuity is quite large, and the water apjiears as a band around its 

 outside. So rapidly does the fluid rotate under high pressure that 

 bodies carried in it are invisible. If a very small body be put in such 

 a nozzle and 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 XYI, Fig. 6, is seen a coarse, bevel-lipped side-slot, s, in the 

 tubular part, «, 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 in planes at various other angles, which may be especially of 

 advantage in spraying upward. 



In Plate KYI, Fig. 7, a similar nozzle is shown, differing chiefly in tlie 

 use of a plug, c, in place of a cap, and having the deflecting rim oppo- 



