26 
BULLETIN 230, U. S. DEPARTMENT OF AGRICULTURE. 
bars is not seriously weakened by the addition of oil in amounts up to 
10 per cent. 
Note. — A public patent has been granted for mixing oil with Port- 
land cement concrete and hydraulic cements giving an alkaline reaction, 
and therefore anyone is at liberty to use this process without the pay- 
ment of royalties. 
Caution. — The addition of any waterproofing or damp-proofing agent to cement mortar or concrete is 
valueless unless extreme care is exercised in proportioning, in mixing, and in placing the concrete. 
Q 
