228 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 



hopper less than it does to flour while its periphery is undermined^ the 

 outside of the column of poison will settle down best to where the blast 

 can feed itself therefrom. In case dry poisons or mixtures that are not 

 adhesive, and that jar through the small outlet of an ordinary hopper too 

 easily are to be used, their flow may be regulated by a small plate adjust- 

 able beneath the outlet and essentially on the plan described above. 

 In such cases it is sometimes preferable to mount the i>late on a single 

 screw or support opposite and working through the blast in opposition 

 to the small outlet of the hopper. 



Two other plans for hopper supply are shown in PlateXXYIlI, Figs. 

 4 and 5. These also do not allow the powder to gravitate directly down- 

 ward into the blast,/; but the hopper, P, is closed tight above by a re- 

 movable screw-cap and narrows downwardly. The powder from its 

 lower part has to be acted upon laterally by the blast, at the point o, 

 in Fig. 4, and downwardly at o, in Fig. 5, where the hopper-throat curves 

 around to open beneath. In either of these cases the communication, 

 0, of the blast with the- powder may be much elongated and can be ad 

 justably opened or closed by a slide-plate. The latter or the wall instead 

 may have atn area of many perforations, similarly located, or a slot or 

 ^ots for such powders as feed too strongly by other methods. These 

 two forms of hopper I do not find so satisfactory for flour mixtures as are 

 the forms with adjustable base slots previously noticed for feeding 

 blasts. 



Finally, it should be added that powder can be fed by introducing 

 in the yent of the hopper a moving reel, or brush, or rod, as has been 

 shown in other machines, but these add complications and work less 

 satisfactorily than the arrangement presented with the first feeder de- 

 seribed above. 



The blower drum or casing is preferably made light, of stout zinc, 

 brass or other sheet-metal. It need not be over a foot in diameter, and 

 had better swell gradually in the direction of rotation to its ex-current 

 orifice, as in Plate XXYIII, Fig. X, d^ although the true cylindrical 

 form will answer. The head of the drum on one or on both slides should 

 have a large centrar suction-opening equal to one-third or onehalf 

 of its diameter and with a stiff wire rolled in its margin. For making 

 a blast through only one or two pipes the drum should be very short 

 with the heads only 3 or 4 inches apart. This distance can be multi- 

 plied by any number of pipes desired. 



Pipes for conducting the air blasts should be round, smooth, and 

 bright. Tin suits well when not rusty, but is easily bent, unless of 

 heavy grade. Zinc is preferable, if not acted upon by corrosive chem- 

 icals, as it does not rust from the effects of atmosphere and moisture. 

 Oilcloth spouts kept expanded by a spiral of wire 18 feet long proved 

 flexible, strong, and light, but too rough. Friction destroys the blast 

 of the ordinary rotary blower very quickly. Crooks should also be 

 avoided-, and are D)uch more objectionable in pneumatic blasts than in 



