WASHING AND GRADING SAND FOR CONCRETE. IX, 
When we come to compare Professor Sherman’s results 
with Captain Jadwin’s, a very marked difference is observed 
and one is forced to the conclusion that the kind of clay, 
or so called loam, isa factor in the results. Atthe same 
time even Captain Jadwin’s results show that an admix- 
ture of 10% clay and 15% loam is not much inferior to the 
standard sand. 
No doubt washing sand removes not only the clay or 
vegetable matter, but also the fine sand particles, and 
the resulting mortar is not sosolid. It is clear from above 
experiments that rich soil, resulting from decayed vege- 
table matter, should at least be removed from concrete 
sand. 
In connection with the water supply works, Penzance, 
F. Latham, . mst. c.5., among other tests made the follow- 
ing experiment :—Ten briquettes were made with material 
taken from the works. In some cases the materials were 
carefully measured in accordance with the stereotyped 
specifications (1 of cement and4 of sand, &c.), andin others 
care and judgment were used, placing a little finer sand in 
the mixture, and a larger proportion of sand to fill up the 
voids in the gravel. 
The briquettes were proportioned 1 to 7 of aggregate, 
and the result was that the 1 to 7 briquette stood 115ibs. 
tensile strain, and the cther stereotyped mixture, in the 
proportion of 1 to 4, stood but 45Ibs., after 21 days immer- 
sion in water in each case. 
On examining the careful gauging of 1 to 7, and com- 
paring it with samples containing the higher percentage 
of cement, it was observed that there was an appearance 
of excess of cement showing on the trowelled surface of 
the former, and insufficient cement in the latter, although 
the proportions in which the cement was actually used 
were the reverse. 
