2 
Mr Fairbairn on Fireproof Warehouses. 118 
area of about 11 inches in 30 feet, which, taken at 25 tons to 
the square inch, will give a resisting tensile force of 275 
tons. In factories, the resisting powers of the tie-rods sel- 
dom exceed 100 to 110 tons, which is under 4 tons to the 
foot, whereas the resisting forces in warehouses should not 
be le*s than from 9 to 10 tons to the square foot. 
In the construction of fireproof buildings, it is not only 
necessary to secure the ends of the beams by extension rods 
embedded in the walls, but the arch-plates, or ‘‘ Skewbacks,” 
at each end should also be built into the wall; and this 
plate, as well as the ends of the beams, slightly raised above 
the level of the column, in order to allow for the settling of 
the walls, which invariably takes place as the weight in- 
creases in their ascent. 
For the strongest form and best position of columns sup- 
porting heavy weights, we must again refer to Mr Hodgkin- 
son as the very first authority. In his valuable treatise on 
the strength of pillars of cast-iron and other materials, pub- 
lished in the Philosophical Transactions, Part I1., for 1840, 
and for which he received the gold medal of the Royal 
Society, will be found some of the most interesting and most 
useful experiments yet given to the publie. 
From these researches it will be necessary to make some 
extracts, in order to ascertain the laws connecting the 
strength of cast-iron pillars with their dimensions, and to 
determine the best and strongest form adapted to the sup- 
port of heavy weights. The first experiments were made 
upon solid uniform pillars, mostly cylindrical, with their 
ends rounded, in order that the force might pass through 
the axis; the next were of the same dimensions, with flat 
ends at right angles ; and others again with one end rounded, 
and the other flat to the axis. They were broken at various 
lengths, from five feet to one inch (some with dises turned 
flat), and form a series of most interesting results. The 
pillars with discs gave a small increase of strength above 
those with flat ends, but the approach to equality between 
the strength of pillars with discs, and those of the same 
VOL. XXXVIII. NO. LXXV.—JAN. 1845. H 
