METHODS OF HATCHING FISH EGGS 
209 
DESCRIPTION OF THE McDONALD UNIVERSAL HATCHING-JAR. 
The jar consists essentially of a cylindrical glass vessel with hemispherical bot- 
tom. These are not blown, but pressed, in order to secure regularity of the interior 
surface, upon which depends to some extent the perfect working of the jar. The jar 
is supported upon a tripod of three glass lugs, which form of attachment was adopted 
to prevent the distortion of the bottom of the jar — a defect frequently found in jars 
resting upon a single foot. The top of the jar is made with threads to receive a screw 
cap, and both the bottom and top surfaces are ground so that the plane of each shall 
be at right angles to the axis of the jar, and so that when the jar is resting upon its 
feet its axis shall be perfectly vertical. These are all-important considerations to 
secure good results in hatching eggs. 
The top of the jar is closed by a metallic disk, perforated with two holes five- 
eighths of an inch in diameter; one central, which admits the glass tube that intro- 
duces the water into the jar ; the other, equally 
distant from the central hole and the edge of 
the metal plate, admits the glass tube which 
carries off the waste water. The central tube 
is connected by a half-inch rubber pipe with 
the jet cock which should furnish a supply of 
water under a constant head. A groove in the 
inner surface of the metallic plate carries a rub- 
ber collar, and when the plate is in place the 
tightening of the metallic screw cap seals the 
opening hermetically. It will sometimes be 
found that a slight defect will cause a small 
leak even after the metal screw cap is down 
tight. This can nearly always be corrected by 
the employment of two rubber collars or wash- 
ers. Both the inlet and outlet tubes pass 
through stufiing boxes provided with gum 
washers and binding screws. The central or 
feed tube is provided with stuffing boxes, one 
on top of the disk and one on the bottom, the 
better to hold it in a true center. The outlet 
tube is provided with only one stuffing box, 
and moreover the binding ring is beveled, the 
purpose of which will be explained later. In 
fitting the jar for work it will be found advantageous to fit in the side tube first. The 
glass tubes should be wet, the gum washer slipped on the tube about 1 inch from the 
end, and introduced into the opening; holding the tube perpendicular to the face of 
the plate, press fairly on the tube, and the washer, rolling on itself, will fall into the 
seat provided for it. Screw on the binding ring, and test by seeing that the tube 
slides freely back and forth in the stuffing box. If not, it should be refitted with a 
heavier or lighter washer, as may be required. The glass tubes can not be procured 
of absolute uniformity in size, and the gum washers, being hand made, also vary; 
therefore in order to secure a neat fit use large washers with small tubes and vice versa. 
Water is the only lubricant that should be used about the jar fitting. 
Bull. U. S F. (J., 88—14 
