6 BULLETIN 230, U. S. DEPARTMENT OF AGRICULTURE. 
A very interesting experiment showing the nonabsorbent and non- 
permeable character of oil-mixed mortar when subjected to low pres- 
sure is incompletely shown in Plate IV. Four mortar receptacles, 
8 inches in outside diameter, 2 J inches high, and with walls and 
bottom one-half inch in thickness, were immersed in water to a 
depth of about 2 inches after they had cured in moist air for one 
week. A mortar mixture of 1 part of cement to 3 parts of sand was 
used. Specimen No. 1, which contained no oil, showed a damp spot 
on the inside after immersion for about one minute. After one 
hour's immersion it was damp over the entire inner surface to a 
height somewhat greater than the level of the water in the dish. 
This was caused in part by capillarity. Within a few days water 
had penetrated this receptacle until the level inside was the same 
as that outside. The remaining three vessels, made of 1:3 mortar 
and mixed with 5, 10, and 20 per cent of oil, respectively, remained 
perfectly dry on the inside during immersion for one year. 
All of these experiments have given very encouraging results and 
point to the use of oil-mixed mortars and concretes as a cheap and 
effective solution of the problem of waterproofing for a great many 
types of concrete construction. 
MATERIALS USED. 
As ordinarily made, concrete consists of a mixture of cement, sand, 
broken stone or gravel, and water. Oil-mixed concrete differs from 
ordinary concrete only in that oil is an additional ingredient in the 
mixture. It is important that the materials used in any concrete 
mixture be of the proper kind and be combined in the correct pro- 
portions for the work in hand. 
CEMENT. 
By far the best cement for use in oil-mixed concrete is Portland 
cement, not only because of its more uniform quality, but also be- 
cause of its greater strength, which permits it to be mixed with a 
larger percentage of properly proportioned aggregate. For unim- 
portant work it is usually safe to select a brand of cement of well- 
known reputation and use it without testing, although even for 
work of an insignificant character it is preferable to test the cement 
for its soundness or its liability to disintegrate. 
A very quick test for soundness may be made by kneading some of 
the cement with enough water to form a paste of such consistency 
that it may be molded into a ball without crumbling. This ball, 
which should be about 1J inches in diameter, should be allowed to 
harden under a moistened cloth for 24 hours, after which it should 
be placed in a pan of cold water, and the water heated to the boding 
point. If the cement ball shows no signs of cracking after boiling 
