1 66 TOWERS AND TANKS FOR WATER-WORKS. 



page 91, and calculations suited to a wide range of heights 

 and diameters of metallic cylinders have been given, so that 

 between these ranges it is only necessary to revert to the tables 

 to find the required theoretical thickness of the metal in frac- 

 tions and decimals of an inch corresponding to the required- 

 height and capacity. 



Thickness of Plate. Considering a 24-ft. X i2O-ft. stand- 

 pipe, the theoretical thickness of the lower plate is seen to be 

 J of an inch. 



Determining to advance by i6ths, twelve subdivisions of the 

 horizontal line equal of an inch thickness of plate. Draw 

 the diagonal line H ' B, which is a line which indicates the 

 theoretical thickness of the plate from zero at H, and where 

 the thickness and strength of a piece of letter-paper is capable 

 of resisting the pressure of the water, to B, where f of an inch 

 of steel, having a tensile strength of 60,000 Ibs. , with a factor 

 of safety of 4, and a rivet-efficiency of f the ultimate strength 

 of the plate, is required to safely resist the hydrostatic press- 

 ure of 51.97 Ibs. per square inch. 



From the subdivisions of the vertical line H' H, draw per- 

 pendicular lines parallel to the base-line, with a distance 

 apart of 5 ft. by the assumed scale, and with each length equal 

 to the theoretical thickness of the plate, measured by the scale 

 of the base. The length of these lines, representing the theo- 

 retical thickness of the plate, can be determined mathemati- 

 cally by the formula given, or from the table, as was done 

 when establishing the thickness of the lower plate ; but, to sim- 

 plify this process, the length of each horizontal line can be 

 determined graphically by terminating that line at the inter- 

 section formed by vertical lines, projected from the scale of 

 the base, but which are not usually indicated except to -com- 

 plete the parallelogram. 



If the parallelogram as thus formed lies inside of the 

 diagonal line, the plate of which it is intended to construct 



