RAILWAY CONSTRUCTION. 299 



Fig. 452 shows an ordinary derrick crane, which, on account 

 of the large and varying sweep of the jib, is found very con- 

 venient for certain classes of work. It occupies a considerable 

 amount of room, and its adoption is therefore limited to situa- 

 tions where space is of secondary importance. 



All the cranes described above are shown as worked by hand- 

 power, but they may be worked by steam, hydraulic machinery, 

 or electricity. Manual power will be the most economical 

 where the use of a crane is only occasional, but it would be too 

 slow and costly where there is constant heavy work. 



Water-tanks. A supply of good water forms an important 

 item in railway working, and ample provision must be made at 

 all principal stations for the requirements of engines and general 

 station purposes. According to the locality, the water may 

 either be procured from the main of some established water- 

 works company, or be pumped from a well, or forced up from a 

 stream by a ram, or brought down by gravitation in pipes from 

 a spring or stream at a distance. Water thus obtained is con- 

 ducted into tanks placed at a height of 18 or 20 feet, or more, 

 above the level of the rails, and forms a storage supply from 

 which deliveries can be made at a fair pressure and in large 

 volume. The tanks may be made of cast-iron, wrought-iron, or 

 steel, or even of wood. In the great timber-producing countries 

 abroad, water-tanks, some of them of large capacity, are very 

 frequently made of wood, the circular or half-cask form being 

 preferred ; but at home, and on European lines generally, wooden 

 tanks are rarely used except for temporary purposes. Cast-iron 

 being less liable to deterioration from rust than wrought-iron or 

 steel, is much used for water-tanks. 



Figs. 453 to 457 are sketches of a medium-sized cast-iron 

 water-tank, to hold about 7800 gallons. The size may be varied 

 both in length, width, and depth, without in any great measure 

 altering the type. The lower portion, or tank-house, may be of 

 stone, brick, wood, or iron framework, and may be utilized as a 

 pump-room, store, or lamp-room. In the sketch given a row of 

 cast-iron girders are placed across the top of the walls of the 

 tank-house, to carry the tank, the plate-joints of the latter being 

 made to coincide with the centre lines of the girders. The 

 lower and upper edges of the tank-plates are shown curved in 

 section, the former for appearance and facility of cleaning, 

 and the latter to check the tendency of the water rippling or 



