94 CONSTRUCTION 



vertically on the plank with one edge exactly on the center 

 line of the trench. This strip must be plumb. Then by 

 the use of a wye-level, a mark is made on the side of strip 

 and a nail driven a whole number of feet above the invert 

 elevation. This is also done at the next 50 feet and a 

 string stretched between the nails. The string may thus 

 be stretched for some considerable distance at the given 

 number of feet above the invert grade line. Errors in 

 level work are easily detected. If by reason of an abrupt 

 change in cut the line strikes the board, or too high or too 

 low above or below it, the string may be lowered or raised 

 a foot or two. The usual methods of pipe-laying and in- 

 spection should be followed and will not be discussed in 

 this connection. (See Fig. 30, page 91.) 



Wet trenches can be kept free from water by use of a 

 hand-pump or the pulsometer (see Fig. 28, page 83). In 

 park work a hoisting engine is generally available and 

 connection may be made between the pulsometer and the 

 boiler of the hoisting engine, a low fire being kept up 

 over night by the night watchman. In the morning the 

 trench will be in a suitable condition for work. 



The backfilling should be tamped in layers. If the 

 main line trench is filled in before the laterals are laid, a 

 plank is placed in a vertical position against each wye 

 connection and sufficiently long to project above the 

 ground. 



GRADING 



Staking Out the Work. Grade stakes are set at the in- 

 tersections of the cross-section lines and at every change 

 of slope. The stakes are marked on the side with the proper 

 cut or fill measured from the top of stake or they are so 

 driven that their tops are to grade, in which case the tops 



