STATE GEOLOGIST. 33 
much less than with the quartz, but showed no regularity with variations 
in the use of water in the mortar. The lowest permeability with lake sand 
mortar was obtained when 14 to 16 per cent. of water was used in the 
mottar. The wetter mortar required less tamping and more mortar to 
fill the collar, thus indicating a denser mixture. | 
In testing grout washings, the clear mortar disc was first tested under 
pressure, then washed with a grout of one part cement and one part water, 
allowed to set 24 hours and placed under pressure. Another washing was 
applied, the disc allowed to set 24 hours and tested again. According to 
the tests the first wash was most beneficial. 
The final conclusions were: 
The permeability of mortar depends upon— 
ist, Une raIn© Oh Sala! Wo) CenneNe. 
and. The voids in the sand. 
3rd. The percentage of water used in making the mortar. 
4th. The thickness of mortar. 
5th. The head of water pressure. 
6th. The amount of tamping. 
The permeability can not be materially reduced by the application of 
soap and alum solutions, or by finely powdered loam used in the sand. 
Permeability can be reduced— 
Ist. By the application of I to 5 coats of cement grout, the reduc- 
tion amounting to from 70 to 98 per cent. of the initial leakage. 
and. Bya coating of neat cement mortar % inch thick. 
ard. Bythe mortar surface standing under a head of water con- 
taining suspended matter. 
LOAMY SAND. 
The majority of engineers specify that the sand shall be clean and 
sharp. A series of tests carried on at the Ohio State University under the 
direction of Prof. C. E. Sherman, also the results obtained by a class in 
cement testing under the writer, seems to prove that clay or loam up to 
I5 per cent. of the weight of the sand adds strength to the mortar. If 
additional tests under the varied conditions arising in practice continue 
. to prove satisfactory, this will mean.a great economy in many pieces of 
work where bank sand can be substituted for lake or washed sand. 
The series of tests referred to were carried on during the winters of. 
I901, 1902 and 1903, by eight students of the Ohio State University, 
grouped two and two in investigations upon the effect of clay and loam in 
sand upon cement mortar. Each thesis embraced the results of such tests 
with Dyckerhoff cement and some standard American Portland. The mor- 
tar was made of I part cement and 3 parts sand, a definitepercentageof — 
3—S. G. 
