900 PROCEEDINGS OF SECTION J. 



which the use of this or tliat kind of sand is capable of 

 occasioning', rarely amounts to more than I, but it exceeds J 

 with the mortars made from hydraulic or eminently hydraulic 

 lime. That is, if the maximum hardness in the two cases be 

 100 the minimum will not be far from 80 in the first case 

 and 60 in the second. 



The general opinion has been that pit sand is better than 

 river sand. It is usually roaglier and more angular, and 

 whether rightly or not, it is certain tliat these qualities are 

 valued l)y most practical builders. 



Sea sand has been condemned by many as the worst that 

 can 1)6 used. Sraeaton in building the Eddystone lighthouse 

 found mortar made with salt water just as good, if not better 

 than that made from fresh ; so that in his case we may 

 suppose sea sand impregnated with salt would have made 

 equally good mortar as fresh -water sand. 



Davy, in his " Treatise on Foundations," remarks, " It is 

 almost unnecessary to observe that washed sea sand will pro- 

 duce precisely the same eftects as the best river sand." Now 

 it is probable that the diflei-ence of opinion on this subject 

 may arise from the different kinds of lime that have been 

 used. Fat lime will not harden if kept damp, and the 

 presence of salt in the mortar will always tend to keep it so. 

 Hydraulic limes, on the other hand, harden all the better, 

 though not so quickly, from being kept damp, and it is therefore 

 reasonable to suppose that in their case sea sand is not pre- 

 judicial. For internal plastering sea sand is evidently unfit, on 

 account of the moisture which keeps exuding from it, dis- 

 figuring its appearances, and making the room damp and 

 unwholesome. Builders, however, seem agreed that sand 

 should be clean. This is a most important point, and one by 

 no means sufficiently attended to. Good mortar can never be 

 made where the sand is filled with earthy and loamy particles, 

 and the fact of these particles being argillaceous adds nothing 

 to their advantage, as uncalcined argil does not possess any 

 properties of value in mortar making. Treussart recommends 

 that sand should be washed in masonry basins from 7 to 10 

 feet wide, from 12 to 16 feet long, and about 2i feet deep, 

 laid about a foot thick, water let over the sand, and well 

 stirred up, allowing time for the sand again to sink to the 

 bottom ; the water should be suddenly let off* by a sluice at the 

 one end, and the operation should be repeated till the water 

 passes off but slightly turbid, when the sand may be considered 

 clean, 



