CHEMICAL AND PHYSICAL PAPERS. 85 



of clay or loam in sand, up to about fifteen per cent., was to increase 

 rather than to decrease the tensile strength of the mortar. This in- 

 vestigation, so far as the writer knows, is the most extended that has 

 been made on this subject. 



In view of the data above presented or referred to, it would seem 

 to be a waste of money to require small amounts of earthy material 

 to be washed out of sand that is to be used for Portland cement 

 mortar, whether that mortar is to be used in ordinary masonry or in 

 concrete. An exception to this conclusion might be taken if the 

 mortar were to be placed under water, or if a quick-setting mortar 

 were desired, but experimental evidence on these points is still lack- 

 ing. For the general uses of cement mortar, the conclusions stated 

 above would hold good. 



