USE, CONSTKUCTION, AND COST OP SERVICE RESERVOIRS. 159 



at the bottom, stands down in this groove, leaving a space outside 

 of §" wide which is caulked with rust joint cement ; the inner 

 space is f " wide, into this is inserted one edge of a curved lead 

 expansion ring made from 101b. sheet lead, about -fa" thick. This 

 lead ring is curved with a radius of about 2\'\ and well lapped 

 and soldered at the ends. One edge is dropped into the groove and 

 then fixed by running in molten lead which is well caulked. 

 The other edge of the ring is flattened out and laid down against 

 the vertical edge of the concrete base and well beaten in and 

 then the brick floor is laid, great care being taken to bed the 

 bricks well in mortar and set them hard in against the lead, thus 

 providing a water-tight connection between the shell and the 

 concrete floor. The work was in the first instance executed as 

 above specified, but as there was always some doubt as to what 

 pressure the lead ring would stand before it collapsed with the 

 water pressure, care was taken, when filling the first tank made 

 in this way, to let off the water before it was quite full and 

 examine the ring, ifc was then seen that a tendency to collapse 

 was shewing itself. Orders were then given to cut holes in the 

 top of the ring at frequent intervals and fill it completely with 

 sand and solder up the holes again. The tank was then filled 

 and found to be a success, Further precautions are being taken 

 with two of the larger tanks last completed. 



A single course of bricks nine inches wide is being set on the 

 bottom all round, end on towards the ring and standing about 

 one and a half inch from it, the space between the brick and 

 the ring is being filled with pure asphalte which will be soft 

 and ductile enough to be compressed by the water pressure into 

 any vacancy that may occur should the lead not be quite firmly 

 set against the concrete base. 



The Diagram on Plate xvn. shews the strength of this tank 

 to resist bursting pressure, from this it will be seen that, allowing 

 eighty per cent, of the strength of the plates for loss in the joints, 

 the tank has a minimum factor of safety of six; the load being 

 uniform and steady such a factor may seem unnecessary, but it is 



