﻿Orifices, and JSntrainment of Air by the Issuing Jet. 973 



the endeavour was made to make the orifices as circular and 

 smooth as possible. In the case of the orifices numbered 1- 

 10 in the sequel, these were made in a stiff copper-nickel 

 alloy (88 per cent. Ni, 12 per cent. Cu), 0*0229 cm. thick, 

 and except for the smaller ones were made, by means of a 

 machine designed by Dr. Charles Carpenter tor the bulk 

 manufacture of single or multiple-orificed injectors for use 

 in gas-burners. By this machine, a disk about 6 mm. in 

 diameter is cut from a sheet of metal, and simultaneously a 

 hole or holes punched in the disk by the passage of a flat- 

 ended accurately cylindrical needle or needles through the 

 disk, which is held meanwhile between blocks, the lower 

 carrying the needle or needles, which after passing through 

 the disk enter accurately bored holes in the upper block. 

 The machine is operated after the manner of an embossing 

 press. 



Orifices in disks prepared in this manner possessed a very 

 smooth interior surface, and there was little burr on their 

 outer surfaces. This was readily ground away by rubbing 

 on an oiled stone, and the inner surface finally burnished by 

 means of a cylindrical needle. 



The two smaller orifices employed were drilled in the same 

 material, great care being taken to see that they were as 

 accurately circular, and their interior surfaces as smooth as 

 possible. 



Fig. 3 (PL VL) shows microphotographs (linear magni- 

 fication about 37) of representative orifices of the series. They 

 indicate very slight departure from the circular form. Actual 

 measurement showed that the greatest and least radii of any 

 disk agreed to within 1 per cent, except in the case of No. 8, 

 where a maximum difference of about 2 per cent, occurred. 

 A microscopic examination of the interior of the orifices 

 showed that there was present very little roughness in 

 the finished orifices. 



The prepared disk was carefully soldered on to a cap which 

 screwed on to the lower end of the tube B (fig. 1), this cap 

 being then itself soldered on to the tube. It was previously 

 ascertained that all joints in the various parts of the apparatus 

 were gas-tight. Tested under 10 inches of water pressure at 

 various times during the course of the experiments, the leak 

 in the discharge tube when the orificed disk was replaced by 

 a blank of the same thickness, and in the anemometer tube, 

 was found not to exceed 0*001 cubic feet per hour. 



