Thickness^ Cement and Materials of Walls. 20.3 



others \vlio say, that the bodies ai-ound which the lime 

 crystallizes, should be sound, and incapable of being 

 cnu^hed. On a comparison with some Delaware tide 

 water sand, and some pit sand, its superiority was so 

 striking, that the mason would use no other ; after a fair 

 and long trial of the quahties of this. It assisted the 

 crystallization of the cement in a greater degree, and in 

 less time, than any other sand, within reach of the work. 

 It was pure, and free from any foreign mixture of 

 loam or mud. All alloys of the latter kind, are injuri- 

 ous; because they are crushed, and cannot resist, but 

 yield to, the pressure of crystallization. The place from 

 which it was brought, ensured its being free from any 

 saline particles. Y or pointings it required no washing; 

 being of itself sufficiently pure. 



This specification is not given, as a character pecu- 

 liar to this sand ; compared with that material in similar 

 situations. But it is mentioned, with a view to recom- 

 mend to all who build where the best cement is essen- 

 tial, and river sand attainable, to procure it from the 

 highest accessible parts of streams. The deposits of 

 floods, in these places, are of pure silicious (flinty) mat- 

 ter, brought from pebbly and clean bottoms; with no 

 mixtures, collected from foul and mai'shy shores, or 

 muddy beds of rivers. 



In walls washed by the sea, or streams ; or made to 

 contain water: in thick masonry o^' JbrtiJicationSj millsy 

 and other water works, basons, or other stone work, 

 either constantly or occasionally wet, rich mortar should 

 be invariably shunned. It is believed by many, that 

 mortar, in thick walls or piers, only affords a ^(fofforthe 

 stone ; and never indurates. But this is known to be 



