Page:A Letter on the Subject of the Cause (1797).djvu/43

 rod on all ſides; and being ſecured down by the braſs or iron ring above mentioned, cauſes the rod to ſlide ſteam and air tight. But the quantity of rub which is conſtantly on this part, and the nice perfection required, ſoon diſcovered the want of ſome farther help; and ſomething ſimilar to the means juſt treated on for keeping the piſton tight, ſuggeſted itſelf at an early period of Mr. Watt’s experiments; which is effected as follows:

In the cylindrical part of the box is turned another rebate, about an inch more or leſs above the ring which ſecures the lower packing; and into this rebate is alſo fitted a ring as before, which cauſes a ſpace between it and the lower ring. Then above the upper ring is turned another cylindrical part like the former; having of neceſſity a greater diameter. This conical chamber is likewiſe packed with hemp, junk, &c. and this packing alſo faſtened down by means of a ring, rather more in a plug form, and ſo contrived as to admit of being ſcrewed down at pleaſure for the purpoſe of compreſſing the packing as worn away by the friction of the rod. The ſtuffing box completed, a ſmall tube is inſerted by one of its ends at the ſide of the ſaid box, ſo as to communicate with the open ſpace