58 TOWERS AND TANKS FOR WATER- WORKS. 



For iron, weight of plates and angles 81,600 Ibs. 

 For steel, weight of plates and angles 85,680 Ibs. 



[NOTE. Increased weight approximates an additional weight of %% 

 of steel over iron of like dimensions.] 



Estimated amount of rivets, 4,600 Ibs., including waste al- 

 lowance. 



The estimated cost of the superstructure, therefore, would 

 be as follows : 



81,600 Ibs. iron plates at $1.40 $i 142.40 



85,680 Ibs. steel plates " 1.05 899.64 



Difference in favor of steel $ 242.76 



A comparison of the relative tensile strength of the two 

 metals shows an advantage of about 22$ in favor of steel, and 

 had steel plate been selected, allowing for the increase of 

 strength, the thickness might have been so reduced as to have 

 permitted a reduction of 18,850 Ibs., at the market price, 

 effecting a further saving of $197.92, or a total saving of 

 $440.68 had steel plate instead of wrought iron been used. 



Comparative Cost. In citing this particular I45,ooo-gal. 

 stand-pipe for the purpose of arriving at conclusions as to rela- 

 tive cost of two possible metals, it may be urged that a higher 

 grade of steel should have been insisted upon in order to make 

 the comparison possible ; however this may be, there can be no 

 controversion of the fact that in equivalent metals the greater 

 strength in proportion to volume and weight, gives steel a 

 clear preference of something like 20$ as applied to ruling 

 prices. Such reasons have led to an almost universal demand 

 for steel as a structural metal, and its choice may be conceded. 

 This preference having been allowed, the particular grade of 

 steel best adapted to constructive purposes must receive con- 

 sideration. 



It has been explained that structural steel is the product 



