the base of the column above.

Timber columns are preferred to those of iron, unless the load is
greater than can be sustained by timber.

The floor planks for this type of floor are generally made of spruce
plank from three to four inches in thickness, grooved on both edges and
joined together by hardwood splines. These floor-planks should be two
bays in length, breaking joints at least every four feet.

Above this the top floor, of 1-1/4 or 1-1/2 inch hardwood, is laid, and
in some instances the resistance of the floor to fire is greatly
increased by laying a coat of plaster on the floor-plank before the top
flooring is built. But the general method of increasing the resistance
of the floor to fire is by covering the floor and beams on the under
side with plaster laid on wire-lathing.

Such a mill floor and columns, while possessing in a very high degree
features which offer resistance to the fire, being weakened by the
temperature only to a slight extent as they are slowly burned away under
the exposure to a very severe fire, also possess the merit of great
economy, both as regards the low price of construction, and in that the
floor is thinner in comparison with joisted floors of equal strength,
saving in this respect, for every floor in a building, about ten inches
in height of wall, stairs, belting, steam-pipes, and all vertical
connections reaching from floor to floor, a saving which amounts to
considerable in the total cost of a building.

The division of mills into various portions by means of fire-walls is
frequently not so efficient as assumed, by reason of the lack of