FOR GREAT BRITAIN AND IRELAND. 97 



advantage ; all squaring and facing of stone is also by 

 this means dispensed with, and the required form obtained 

 by moulding the materials, the cement and sand forming 

 the enveloping medium. 



PORTLAND CEMENT. 



In Mr. Stevenson's article on Harbours in the * Ency- 

 clopaedia Britannica,' 9th edition, we have the following 

 important particulars on this subject. 



It must weigh 115 Ibs. to the bushel, and be ground 

 extremely fine, and must stand the following test. 



It is to be made into small blocks, I inch square, 

 8 inches long, and after having been placed in water for 

 7 days, is to be put on two supports 6 inches apart, and 

 must stand a /o-lb. strain. 



Slabs or cakes are also to be made, and after being in 

 water for 24 hours, no cracks or softness must be visible on 

 the surface. 



The cement must be taken from four different bags, 

 must be tested weekly, and the results sent to the 

 engineer. 



It must be brought direct from the manufactory, and 

 kept dry in a store or chamber with both a wooden floor 

 and side walls. 



THE CONCRETE 



is to consist of I part Portland cement, 2 of sand, and 

 5 of gravel, thoroughly mixed with pure water. Large 

 angular stones are to be added after deposit, care being 

 taken that all the stones are completely surrounded by 

 concrete 4 inches thick. All the stones must be per- 

 fectly clean, and free of sea-weed. 



VOL. IX. E. 4. H 



