THE ROYAL ARTILLERY INSTITUTION. 
429 
or button-shaped head projecting into the bore to close the joint; and 
instead of entering the bore vertically* it was fixed upon the side* of the gun 
at an angle of 45° to the vertical axis* in order that it might be more easily 
served (see List of Changes* 1st December* 1868). It was subsequently 
decided (25th November* 1868)* that all wrought-iron guns of 7-inch 
calibre and upwards should have similar vents (Fig. 1)* but let in vertically 
as before* except in the case of guns of 10-inch calibre and upwards* whose 
size would render the vertical position awkward. 
This was acted on for a short time* but the vents not proving satisfactory, 
the employment of the platinum tip was suspended* and steel vents lined with 
copper (Fig. 2)* were used; but as these too did not answer expectations* all 
the big guns are now vented with copper specially hardened* the letter II 
being stamped on the top to indicate the fact.t 
Eig 1. Eig. 2. 
* The vent is on the right side of the gun if intended for broadside purposes, but if for a 
turret gun, the vent is placed on the right or left hand side as convenience demands. 
t The copper is 2 inches square in section. It is drawn down square while cold, under a light 
steam hammer, to the size required for the screw—the blows being as light and numerous as 
possible, so that the greatest amount of condensation may be effected. It is afterwards treated in 
the usual manner— i.e., having a seven-tbread screw, and coned at the bottom. In 10-inch guns 
and upwards, the threads are limited to a length of 6 inches above the cone, the upper part being 
plain. 
[VOL. VI.] 
56 
