Page:A Letter on the Subject of the Cause (1797).djvu/42

 article in the Machine. This is the method of rendering the aperture through which the piſton rod paſſes, conſtantly air and ſteam tight; notwithſtanding the ſaid rod in many Engines ſlides through this aperture no leſs than three hundred and twenty feet per minute during the time they work.

This junction or aperture is a very ingenious contrivance, and called a ſtuffing box. It is a part formed in the center of the cap or top of the cylinder, and is a kind of cylindrical box, of about ſix or eight inches deep, made of iron. The upper part of this box is conſiderably wider than the diameter of the piſton rod above mentioned; and the bottom or lower part next the inſide of the cylinder is made exactly to fit the ſaid rod. From this part, for a ſmall diſtance upwards, the box is turned in a conical form, ſo as to make a chamber exactly in the ſhape of a ſnuf-mull; at the top of this conical part is turned a rebate or ſeat, into which is fitted a braſs or iron ring, the extreme circle of which exactly fits the cylindrical part above the conical part deſcribed. This conical chamber is then filled with hemp or junk, ſo as to ſurround the piſton rod