WA: W E. COOK. 
good. The first sample, which contained 3°2% of clay, gave 
lower tests than the second sample, which contained 15°7? 
of clay. Another test which proved the superiority of sand 
containing clay, was carried out ina different way. Two 
samples of the same sand were taken, one being washed 
and the other not. The unwashed sand proved about 25% 
superior, although it contained 6% of clay. Many other 
tests were made, which tended to prove that the presence 
of small percentages of clay is not objectionable, but on 
the other hand may be desirable. 
“They did not prove, however, that sand containing 
ordinary soil would be better than sand without it, and tests 
were therefore made of washed sand, to which was arti- 
ficially added 2, 5, 10, and 20 per cent of rich surface soil, 
consisting principally of decayed organic matter. Thesoil 
was taken from the bank of the Chicago River, where 
undisturbed weeds decomposed, season after season, and 
made the richest kind of soil. The results were disappoint- 
ing. They were neither inferior nor superior, but proved 
quite irregular. The tests up to 2 years showed that at 
some periods they were above the sand containing no soil, 
while at other times they were below. The percentage of 
soil added did not cause the tests to follow any definite 
law. The 20% adulteration had but little different effect 
from the 2° adulteration. Asa whole the average strength 
of the tests up to 2 years was about the same as the clean 
‘tests; but the irregularity was so great as to make the 
adulterated sands less desirable than the clean sands.”’ 
Mr. Hain’ remarks that the strength obtained from a 
given sand depends to a considerable extent on the proper 
admixture of the fine and coarse particles. In conclusion 
he states that the best mortar sand found in nature is one 
with sharp corners, rough surfaces, grains neither coarse, 
1 Railway and Engineering Review, Chicago, 21st Jan., 1905, page 40. 
