SCIENSITY: Edison Portland Cement

Friday, 25 January 2013

As a casting necessitates a mold, together with a mixture sufficiently fluid in its nature to

fill all the interstices completely, Edison devoted much attention to an extensive series of

experiments for producing a free-flowing combination of necessary materials. His

proposition was against all precedent. All expert testimony pointed to the fact that a

mixture of concrete (cement, sand, crushed stone, and water) could not be made to flow

freely to the small- est parts of an intricate set of molds; that the heavy parts of the

mixture could not be held in suspension, but would separate out by gravity and make an

unevenly balanced structure; that the surface would be full of imperfections, etc.

Undeterred by the unanimity of adverse opinions, however, he pursued his investigations

with the thorough minuteness that characterizes all his laboratory work, and in due time

produced a mixture which on elaborate test overcame all objections and answered the

complex requirements perfectly, including the making of a surface smooth, even, and

entirely waterproof. All the other engineering problems have received study in like

manner, and have been overcome, until at the present writing the whole question is

practically solved and has been reduced to actual practice. The Edison poured or cast

cement house may be reckoned as a reality.

The general scheme, briefly outlined, is to prepare a model and plans of the house to be

cast, and then to design a set of molds in sections of convenient size. When all is ready,

these molds, which are of cast iron with smooth interior surfaces, are taken to the place

where the house is to be erected. Here there has been provided a solid concrete cellar

floor, technically called "footing." The molds are then locked together so that they rest on

this footing. Hundreds of pieces are necessary for the complete set. When they have been

completely assembled, there will be a hollow space in the interior, representing the shape

of the house. Reinforcing rods are also placed in the molds, to be left behind in the

finished house.

Next comes the pouring of the concrete mixture into this form. Large mechanical mixers

are used, and, as it is made, the mixture is dumped into tanks, from which it is conveyed

to a distributing tank on the top, or roof, of the form. From this tank a large number of

open troughs or pipes lead the mixture to various openings in the roof, whence it flows

down and fills all parts of the mold from the footing in the basement until it overflows at

the tip of the roof.