Strength of Bricks.—I.
| Description. | Pressure in tons to | |
|---|---|---|
| Crack. | Crush. | |
| Four white bricks, each | 16.25 | 41.00 |
| Three „ „ „ | 17.05 | 41.05 |
| Red bricks, ordinary | 13.00 | 26.25 |
| Red bricks, not well burned | 13.75 | 25.05 |
| Best Paviours | 14.00 | 23.00 |
| Grey Stocks, London | 12.00 | 14.00 |
Turning to the second table, compiled for the most part from brickmakers’ circulars, and from the original results obtained for the late Building Exhibition, at the Agricultural Hall, all the experiments, we believe, having been carried out by Mr. David Kirkaldy, it will be noted that great variation in strength is apparent, following the different kinds of bricks. The highest result, 1064.2 tons per square foot, was obtained on a blue Staffordshire brick, though that is very closely run by bricks made from slate débris (1056.2 tons) from South Wales. The lowest result, 139.5 tons per square foot, was from a Worcester brick.
Strength of Bricks.—II.
| Locality. | Description. | Dimensions, Inches. | Mean stress of six samples in tons per square ft | |
|---|---|---|---|---|
| Cracked | Crushed | |||
| West Bromwich | Blue | 2.74, 9.03 × 4.36 | 548.6 | 1064.2 |
| „ „ | Blue (another make) | 2.80, 8.75 × 4.12 | 260.7 | 651.0 |
| „ „ | White glazed, “Terra Metallic,” recessed both sides | 3.10, 8.80 × 4.22 3.16, 8.70 × 4.34 | } 225.0 | 273.7 |
| „ „ | Blue vitrified | 2.55, 9.03 × 4.30 | 245.1 | 654.9 |
| Worcester | “Pressed,” recessed top and bottom | 3.20, 9.14 × 4.50 | 65.0 | 139.5 |
| „ | “Builders.” recessed top and bottom | 3.20, 9.30 × 4.50 | 56.1 | 155.5 |
| Saltley, Birmingham | Red, recessed one side | 3.20, 8.90 × 4.35 3.25, 8.95 × 4.40 | } 138.7 | 180.5 |
| Rowley Regis, Staffs. | Blue vitrified no recess | 2.85, 8.75 × 4.20 | 385.6 | 722.7 |
| Leicester | Red, recessed both sides | 2.65, 8.90 × 4.25 2.75, 9.10 × 4.36 | } 105.9 | 150.6 |
| Napton-on-the-Hill, Rugby | Light brown, wire cut | 2.85, 8.92 × 4.20 2.90, 9.10 × 4.25 | } 131.6 | 303.9 |
| Ruabon | Red, no recess | 3.10, 8.75 × 4.28 3.15, 8.73 × 4.29 | } 439.2 | 676.8 |
| „ | Blue, no recess | 3.02, 8.99 × 4.37 3.01, 8.95 × 4.36 | } 358.9 | 561.2 |
| Glogue, Whitland, S. Wales | Slate débris | 2.33, 8.70 × 4.25 | 556.4 | 1056.2 |
| Ravenhead, St. Helens, Lancs. | Red, brown wire cut | 2.90, 9.00 × 4.20 2.90, 8.90 × 4.27 | } 215.8 | 354.7 |
| Earith, St. Ives, Hunts. | Yellow, wire cut | 2.50, 8.70 × 4.10 2.50, 8.80 × 4.20 | } 135.9 | 178.8 |
| Gillingham, Dorset | Red, wire cut | 2.60, 8.90 × 4.30 2.60, 8.90 × 4.25 | } 159.5 | 261.7 |
| Newton Abbot, Devon | Vitrified “granite” | 2.80, 8.90 × 4.35 2.80, 9.10 × 4.55 | } — | 445.2 |
Table III. is by Professor Unwin,[18] and records the strength of several well-known bricks. Professor Unwin’s mode of experimenting we have already alluded to.
Strength of Bricks.—III.
| Description. | Dimensions. Inches. | Cracked, at tons per sq. ft. | Crushed at tons per sq. ft. | Colour. | Remarks. |
|---|---|---|---|---|---|
| London stock | 4.6 × 4.1 × 2.4 | 128 | 177 | Yellow | Half brick |
| „ „ | 4.6 × 4.0 × 2.45 | 133 | 181 | „ | „ |
| „ „ | 9.2 × 4.1 × 2.8 | — | 129 | „ | |
| „ „ | 8.9 × 4.2 × 2.3 | — | 113 | „ | |
| „ „ | 8.9 × 4.25 × 2.5 | — | 103 | „ | |
| Aylesford, common | 8.9 × 4.4 × 2.7 | 48 | 183 | Pink | |
| „ „ | 8.9 × 4.4 × 2.7 | 111 | 228 | „ | |
| „ pressed | 9.1 × 4.3 × 2.7 | 71 | 141 | Red | Deep frog |
| Rugby, common | 9.5 × 4.2 × 2.9 | 158 | 190 | „ | {Between} |
| „ „ | 9.0 × 4.2 × 3.0 | — | 120 | „ | {pine bds.} |
| Lodge Colliery, Notts | 9.0 × 4.2 × 3.4 | 127 | 159 | „ | |
| „ „ | 9.0 × 4.2 × 3.25 | 55 | 122 | „ | |
| Digby Colliery, Notts | 9.3 × 4.1 × 3.25 | 248 | [353] | „ | Not crushed |
| „ „ | 4.6 × 4.2 × 3.2 | 414 | 414 | „ | Half brick |
| Ruabon, pressed | 8.8 × 4.3 × 2.7 | 361 | [361] | „ | Not crushed |
| Grantham, wire cut | 9.2 × 4.4 × 3.2 | — | 83 | „ | |
| Leicester, „ „ | 4.4 × 4.1 × 2.6 | 251 | 337 | Pale red | Half brick |
| „ „ „ | 4.3 × 4.1 × 2.6 | 109 | 308 | „ | „ |
| „ „ „ | 9.06 × 4.2 × 2.8 | 115 | 229 | „ | |
| Cranleigh, pressed | 4.7 × 4.6 × 2.5 | 149 | 181 | „ | Half brick frog. |
| „ „ | 4.6 × 4.6 × 2.5 | 165 | 237 | „ | „ „ „ |
| Candy, pressed | 8.8 × 4.3 × 2.8 | 80 | 381 | — | |
| Gault, wire cut | 8.7 × 4.1 × 3.0 | 111 | 173 | White | |
| „ „ | 4.4 × 4.2 × 2.5 | 119 | 145 | „ | Half brick |
| „ „ | 8.7 × 4.1 × 2.9 | — | 169 | „ | |
| Staffordshire blue, common | 4.5 × 4.3 × 3.0 | 216 | 464 | Blue | „ |
| „ „ „ | 4.3 × 4.2 × 3.0 | 152 | 386 | „ | „ |
| „ „ „ | 8.9 × 4.3 × 3.1 | 240 | [353] | „ | Not crushed |
| Staffordshire blue, pressed | 9.0 × 4.3 × 3.1 | — | 275 | „ | |
| Glazed brick | 8.8 × 4.4 × 3.3 | 69 | 166 | — | Frog. |
| „ „ | 8.9 × 4.4 × 2.9 | 166 | 174 | — |
Table No. III. is specially instructive as indicating the relative strength of several well-known bricks, the experiments being carried out solely for scientific purposes. Yet the figures must not be taken too seriously. Glancing at those relating to “London Stocks,” we find the strength varied from 103 tons per square foot to 181 tons. But more recent experiments made by Professor Unwin[19] on some London Stocks from Sittingbourne, in Kent, shewed that with four samples one crushed at 60.76 tons per square foot and another gave out 94.6 tons, the mean strength of the four yielding 84.27 tons per square foot. With such heterogeneous materials as London Stocks, we ought not to be surprised at these results, but they form a striking commentary on the value of general statements concerning the strength of bricks of varied character going by the same name in the market.
When we consider the strength of homogeneous bricks, and especially where these latter are made of thick marine clays, or where the relative proportions of earths employed are carefully attended to in the raw material, the results appear to be more generally applicable—as far as they go.