STORAGE AND DISTRIBUTION. 135 



thick, J in. round bars placed at 4 in. centre would 

 be the best reinforcement, laid longitudinally and 

 transversely, although a heavy section of expanded 

 metal would also be very suitable, set like the bars 

 4i in. below the upper surface. The tank is sup- 

 ported on cross beams extending from the side wall 

 as shown in the drawings. They are reinforced by 

 three horizontal bars placed 21 in. from the top of 

 the beam. The middle bar is turned up at the ends, 

 as shown, to take shear. The ends of all bars should 

 be fish-tailed. To assist in taking up shear it is also 

 necessary to introduce stirrups of i in. x J in. flat 

 iron. They are bent into the shape of an elongated 

 U, the sides of which would be 20 in. long. They 

 would be placed on the outer bars only. It is im- 

 portant that bars where they cross should be tied to 

 each other by soft wire, B.W.G. 18. The concrete 

 would be composed of four of aggregate, two of sand, 

 and one of cement. The tank in question was de- 

 signed to hold 6750 gallons, weighing about 30 tons. 

 Regarding the water-holding power of concrete : 

 Generous use of Portland cement will secure 

 impervious concrete. Several structures, such as 

 reinforced dams, standpipes, and tanks, have been 

 successfully built with the concrete mixed in the 

 ordinary manner in proportions about i : 2 : 4 or 

 i 12:3, without special care other than to secure a 

 wet consistency. Tests, not here given, show that 

 ordinary sand in mortar in proportions i : 2^ or 

 richer is impervious. Also, so-called sand or silica 

 cements make a somewhat tighter mortar than 

 Portland cements. 



Whether it is cheaper to use the larger quantity 



