376 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bum. 313. 
COST OF SAND CEMENTS. 
In the Portland -cement concrete made in the proportion of cement 
1 part, sand 3 parts, and broken stone 7 parts, it has been found that 
270 pounds of cement will be required for a cubic yard of concrete. 
This, at 2.12 cents per pound, will cost $5.72 per cubic yard. 
In the sand-cement concrete of the proportions 1 cement, 2 sand, 
and 6 stone, 340 pounds of cement would be required for each cubic 
yard of concrete. This, at 1.2 cents per pound, would cost $4.08. 
The saving in the cost of cement to be effected by using sand 
cement instead of the Colton .Portland will be the difference between ! 
$5.72 and $4.08, or $1.64 per cubic yard of this concrete entering into 
the construction of the dam. From the total saving thus realized 
should, however, be deducted the cost of the plant required for grind- 
ing the sand cement. 
Concrete blocks composed of the above proportions were crushed at 
McGill University in 1898, with the following results: 
Sand cement, 1; sand, 2; broken stone, 6; water, 20 per cent. 
Weight per cubic foot, 154 pounds. Crushing load, in pounds per square inch: 
Seven days, 521 pounds; twenty-eight days, 639 pounds; sixty days, 670 pounds. 
A concrete of German Portland of the proportions of 1 cement, 2 
sand, () broken stone, and 20 per cent water stood a load of 728 pounds 
per square inch in twenty-eight days, and one of the same proportions 
made from English Portland stood 698 pounds in twenty-eight days. 
Tests for crushing strength on 6-inch cubes of concrete, made of 1 
part sand cement, 2 sand, and 3 parts gravel, were made on concrete 
that was taken from the bucket just as it was ready to be laid in the 
foundation of the Cathedral of St. John the Divine, in New York 
City. Each result is the average of the crushing strength of four 
separate cubes, made under exactly the same conditions at different 
periods: 
Pounds. 
7 days old crushed at 77,162 
1 4 days old crushed at 83, 225 
30 days old crushed at 92,465 
Approximate cost of plant for making smut cement; capacity, 2^0 barrels per 
twenty-four hours. 
Crusher (required also for crushing rock for concrete) .... $2, 000. 00 
Mill for coarse grinding . . : 2, 000. 00 
Tube mill for finishing . _ 2, 500. 00 
Engine and boiler '_ 1, 500. 00 
Setting up machinery . 1, 000. 00 
Buildings and bins 1, 000. 00 
Total , _ •_._.. : 10, 000. 00 
Cost of mill per barrel of cement .20 
Add, for concrete making, a power mixing machine 1 , 500. 00 
In making concrete, if a good quality of stone be used and the rock 
be crushed so as to be well graduated as to sizes, thus securing a min- 
