should be placed as nearly in the middle of the
clearance space as possible. By some operators the clearance is adjusted
while running, in the following manner: With the machine running at full
speed the step-bearing screw is turned until the wheels are felt or
heard to rub lightly. The screw is marked and then turned in the
opposite direction until the wheel rubs again. Another mark is made on
the screw and it is then turned back midway between the two marks.
Either method is safe if practiced by a skilful engineer. In measuring
the clearance by the first method, the gage should be used with care, as
it is possible by using too much pressure to swing the buckets and get
readings which could be misleading. To an inexperienced man the taper
gages would seem preferable. In the hands of a man who knows what he is
doing and how to do it, a tapered pine stick will give as satisfactory
results as the most elaborate set of hardened and ground clearance
gages.

Referring back to Fig. 11, at A is shown one of the peep-holes opposite
the intermediate in the third stage wheel for the inspection of
clearance. The taper clearance gage is inserted through this hole both
above and below the intermediate, and the distance which it enters
registers the clearance on that side. This sketch also shows plainly how
the shrouding on the buckets and the intermediates extends beyond the
sharp edges of the buckets, protecting them from damage in case of
slight rubbing. In a very few cases wheels have been known to warp to
such an extent from causes that were not discovered until too late, that
adjustment would not stop the rubbing. In such cases the shrouding has
been turned or faced off by a cutting-off tool used through the
peep-hole.

Carbon Packing Used

Where the shaft passes through the upper head of the wheel-case some
provision must be made to prevent steam from the first stage escaping.
This is provided for by carbon packing (Fig. 12), which consists of
blocks of carbon in sets in a packing case bolted to the top head of the
wheel-case. There are three sets of these blocks, and each set is made
of two rings of three segments each. One ring of segments breaks joints
with its mate in the case, and each set is separated from the others by
a flange in the case in which it is held. In some cases the packing is
kept from turning by means of a link, one end of which is fastened to
the case and the other to the packing holder. Sometimes li