Practically the only cases in which the strength of stonework need be considered by the architect, other than to see that proper construction is provided, are: a, the strength of piers; b, strength of columns; c, strength of lintels.

Strength of Stone Piers. - The following figures may be taken for the working strength of stone piers. The figures in the first column may be taken for a fair quality of work laid in good lime mortar, those in the second column for the best class of work laid in cement:

Concrete............................................

5

to

15

tons.

Rubble............................................

5

to

15

"

Squared stone, -inch joints......................................

15

to

20

"

Sandstone ashlar, -inch joints..............................

10

to

20

"

Limestone ashlar, -inch joints.........................

20

to

25

"

Granite ashlar, -inch joint.........................

30

"

The ashlar to be at least as thick as it is high and well bonded.

Strength of Columns. - A stone column, free from defects, carefully bedded and not exceeding ten diameters in height, should safely carry a load equal to one-fifteenth of the breaking load of stone of the same kind and quality. Any column loaded with over fifteen tons to the square foot should be bedded in Portland cement mortar, of not more than 1 to 1, and the mortar should not be allowed to come within 1 inch of the edge of the column until after the building is done, when the joint may be pointed the same as ashlar. As it is difficult to secure a joint which will stand more than forty tons to the square foot, that should be the limit of load for a stone column, no matter how strong the stone is, unless extra precautions are taken with the joints. The following values may be used for the safe loads of columns of the different stones specified, the shaft of the column being in one piece :

Longmeadow (Mass.) red sandstone, best.. .......... .

35 tons per square foot.

Potsdam red sandstone...........................

40

"

"

Manitou (Colo.) red sandstone, best.............

25

to

30

"

"

Ohio sandstone............................

25

"

"

Fond du Lac (Wis.) sandstone..........

25

"

"

Limestone, Glens Falls, N. Y............

35

"

"

Limestone, Indiana........................

25

to

35

"

"

Limestone, strongest varieties......................

40

"

"

Marble, Lee, Mass..................

40

"

"

Marble, Rutland, Vt..........................

30

to

35

"

"

Granite, any, of good quality......................

40

"

"

If the columns are built up of several pieces the joints should not exceed 3/16 of an inch in thickness, and the bed surfaces should be perfectly true and square to the axis of the column.