lower it, which they do by each holding one end of a rope which passes through it. For pipe heavier than 200 pounds it is advisable to use an ordinary three-leg derrick with light tackle-block. The pipe is then suspended by a rope or chain, with a hook at one end and a ring at the other, passed through the pipe and so hooked that it may be lowered in a horizontal position. A convenient arrangement for holding the pipe consists of a hook (Fig. 19), which should

be at least two thirds the length of the pipe and very strong at the bend. The ring must come beyond the centre of gravity of the pipe to prevent its falling off the hook. By use of this a pipe can while suspended be entered into the bell FIG. 19.-PIPE-LAYING of the one previously laid and much heavy lifting by hand avoided.

Hook.

66

FIG. 20.-APPLIANCE FOR ENTERING" HEAVY PIPE.

This is made of wood or iron, with a loose wheel on either side of the bar at the bottom.

'

Before a pipe is lowered into the trench a "bell-hole should be dug where its bell will come, of such size that when the pipe is in position the jointer can pass his hand entirely under and around the front of the bell. It is convenient to

have a stick exactly as long as two or three lengths of pipe, by which the location of each bell-hole is measured from pipe already laid, the bell-holes being dug for a few lengths in advance of the sewer.

Two men should be employed in laying sewer-pipe, one straddling the pipe last laid, the other in the trench just ahead of it. The latter as the pipe is lowered guides it into place and releases the hook on the lowering-rope, if one is used. The former, holding one end of a length of packing in each hand, places the loop thus formed under and around the pipe about an inch from the spigot end and guides this into the bell of the pipe last laid, taking care that the packing also enters the bell. With a yarning-iron he then pushes the packing up against the shoulder of the bell all around, being first sure that the pipe is "home" in the bell. The other pipe-layer meantime supports the pipe at the bell end and shoves it home. The grade-rod and plumb-bob are then used. If the bell end is too high (the spigot end should be all right, since the previous pipe is) it may, if the soil is loam or loose clay or sand, be forced down a quarter of an inch, more or less, by standing and jumping upon the top of the pipe. (The pipe-layer should never rest his foot inside the pipe to force it down, as this is likely to break the bell or even the pipe.) If the soil is stiff clay or gravel the pipe should be removed and the trench bottom lowered sufficiently with the shovel. If the pipe is too low it should not be raised by placing a stone or piece of wood under it, but should be removed and fine earth placed and rammed in the bottom of the trench. By means of the plumb-bob the pipe should be centred exactly under the grade-line. A convenient way of doing this is to suspend the bob from the cord at a gradeplank, being careful not to lower the cord by its weight; then, when the eye is so placed that the cord and plumb-bob string coincide, the former is projected by the eye vertically

into the trench and should cut the centre of the pipe. With a circular salt-glazed pipe the centre is known by a streak of light reflected from the sky, and this streak should be bisected by the vertical projection of the grade-cord. Another plan for obtaining a vertical projection of the grade-cord is to stretch another cord a foot or two vertically below it. But this method is less accurate in practice than the other and is not recommended. The grade-cord cannot be stretched so tight that it will not sag to of an inch at the centre, but allowance may be made for this in using the grade-rod. The foreman or inspector who uses the grade-rod will need to have a short movable plank spanning the trench just ahead of the pipe being laid, on which to stand.

As soon as a pipe is in position sufficient earth should be placed and rammed on each side of it just back of the bell to prevent its moving. The next pipe is then lowered and set,

and so on.

At least two joints behind the pipe which is being set is another man, who cements the joints. The cement he usually keeps in an iron pail of ordinary size (although one having the shape of a pan would be better), just enough being mixed at a time to permit his using it all before it stiffens. If there is any delay in laying the pipe the pail should be cleaned out lest the cement set in it. The jointer should wear rubber mittens, and a small trowel will be found more convenient than the fingers for getting the cement out of the pail. The cement mortar should ordinarily be about as stiff as putty, but if the trench is wet it should be as dry as it can be and have any cohesion. The jointer takes a handful of mortar in each hand and presses it into the bell all around, drawing his hands meantime around the joint. With a wooden or iron calking-tool he compacts the cement in the joint, adding more as is necessary, and with additional mortar he makes a neat bevel outside the beil, continually pressing the mortar

firmly towards the bell. This bevel should not be flatter than 45°, since if too much mortar be outside the bell its weight may cause it to fall away from the pipe and perhaps draw with it the mortar from inside the bell. The compacting of the cement is frequently omitted, but is necessary if tight joints are to be obtained.

Just behind the jointer should be another man, who, as soon as a joint is made, fills the bell-hole carefully with fine earth well tamped, and then fills and tamps the same material under and around the rest of the pipe up to at least its middle. His tamping-bar should be of wood, there being danger of breaking the pipe if the ordinary iron ones are used, and with a face about 2 X 4 inches. If the trench is wet so that water collects in the bell-holes the mortar is likely to become softened and fall out of the joint. To prevent this a piece of cheese-cloth may be wrapped tightly around the joint after it is made, as specified for sub-drains; or the bell-hole may be immediately filled with concrete thoroughly compacted. The latter is the better but more expensive plan. Where there is much water in the trench it is strongly recommended that concrete be placed not only in the bell-holes but entirely around the pipe at the joints (see Art. 46).

In making the joint it is quite probable that some cement will be squeezed into the pipe, forming a ridge or lumps on the inside. To remove these a bag or disk should be drawn through the pipe past the joint as soon as it is finished, which is done by the pipe-layers. The bag may be an ordinary cement or similar sack, somewhat larger than the sewer, filled with straw or excelsior and a rope tied around its mouth and carried through the sewer, being passed through each pipe as

CLEANING DISK.

it is laid. The bag should fit snugly against FIG. 21.-PIPEthe pipe all around. Instead of the bag a disk of heavy rubber packing bolted between two smaller

wooden disks and fastened to an iron rod may be used, being drawn forward as in the case of the bag. The rubber disk should be slightly larger than the sewer.

When a manhole or other break in the sewer is reached in the pipe-laying the last pipe before reaching and the first after leaving it should be omitted or left with uncemented joint, to be laid while the manhole or other appurtenance is being built. This is on account of the probability of such pipe being disturbed or broken during the construction of the masonry before it has been walled in. In this or any case where a stretch of pipe ends, or when the laying is temporarily stopped, a plug should be inserted in the end of the last pipe, and a bar or stake driven against it into the ground or nailed to the sheathing to hold it in position. The last joint should be left uncemented until laying is renewed.

In setting branch specials the earth where the special will come should be so excavated as to permit the branch to rest upon it firmly when in the desired position. If necessary earth should be placed and tamped under the branch for this purpose. The inspector must not forget to examine each branch to see that a cover is cemented in it, unless the houseconnection is to be built at once, and also to mark its location. In wet soil particularly uncovered branches may give rise to serious difficulty, and an unlocated branch is worse than none at all.

If work must be done in the winter-time great care should be taken to prevent the mortar from freezing and to keep ice and frozen dirt out of the joints. In pipe-joints this is not very difficult if the trenches are at all deep, since in these the temperature seldom falls below 40°. But the sand for mortar should be heated, and the pipe also, to insure the removal of all frost from the bells and spigots. In shallow trenches the joints should be covered as soon as possible with at least two feet of unfrozen earth. Care should be taken, particularly