THE inventions that have been thus far described fall into two classes—first, those that were fundamental in the great arts and industries which have been founded and established upon them, and, second, those that have entered into and enlarged other arts that were previously in existence. On coming to consider the subject now under discussion, however, we find ourselves, at this writing, on the threshold of an entirely new and undeveloped art of such boundless possibilities that its ultimate extent can only be a matter of conjecture.
Edison's concrete house, however, involves two main considerations, first of which was the conception or creation of the IDEA—vast and comprehensive—of providing imperishable and sanitary homes for the wage-earner by molding an entire house in one piece in a single operation, so to speak, and so simply that extensive groups of such dwellings could be constructed rapidly and at very reasonable cost. With this idea suggested, one might suppose that it would be a simple matter to make molds and pour in a concrete mixture. Not so, however. And here the second consideration presents itself. An ordinary cement mixture is composed of crushed stone, sand, cement, and water. If such a mixture be poured into deep molds the heavy stone and sand settle to the bottom. Should the mixture be poured into a horizontal mold, like the floor of a house, the stone and sand settle, forming an ununiform mass. It was at this point that invention commenced, in order to produce a concrete mixture which would overcome this crucial difficulty. Edison, with characteristic thoroughness, took up a line of investigation, and after a prolonged series of experiments succeeded in inventing a mixture that upon hardening remained uniform throughout its mass. In the beginning of his experimentation he had made the conditions of test very severe by the construction of forms similar to that shown in the sketch below.
This consisted of a hollow wooden form of the dimensions indicated. The mixture was to be poured into the hopper until the entire form was filled, such mixture flowing down and along the horizontal legs and up the vertical members. It was to be left until the mixture was hard, and the requirement of the test was that there should be absolute uniformity of mixture and mass throughout. This was finally accomplished, and further invention then proceeded along engineering lines looking toward the devising of a system of molds with which practicable dwellings might be cast.
Edison's boldness and breadth of conception are well illustrated in his idea of a poured house, in which he displays his accustomed tendency to reverse accepted methods. In fact, it is this very reversal of usual procedure that renders it difficult for the average mind to instantly grasp the full significance of the principles involved and the results attained.
Up to this time we have been accustomed to see the erection of a house begun at the foundation and built up slowly, piece by piece, of solid materials: first the outer frame, then the floors and inner walls, followed by the stairways, and so on up to the putting on of the roof. Hence, it requires a complete rearrangement of mental conceptions to appreciate Edison's proposal to build a house FROM THE TOP DOWNWARD, in a few hours, with a freely flowing material poured into molds, and in a few days to take away the molds and find a complete indestructible sanitary house, including foundation, frame, floors, walls, stairways, chimneys, sanitary arrangements, and roof, with artistic ornamentation inside and out, all in one solid piece, as if it were graven or bored out of a rock.
To bring about the accomplishment of a project so extraordinarily broad involves engineering and mechanical conceptions of a high order, and, as we have seen, these have been brought to bear on the subject by Edison, together with an intimate knowledge of compounded materials.
The main features of this invention are easily comprehensible with the aid of the following diagrammatic sectional sketch:
It should be first understood that the above sketch is in broad outline, without elaboration, merely to illustrate the working principle; and while the upright structure on the right is intended to represent a set of molds in position to form a three-story house, with cellar, no regular details of such a building (such as windows, doors, stairways, etc.) are here shown, as they would only tend to complicate an explanation.
It will be noted that there are really two sets of molds, an inside and an outside set, leaving a space between them throughout. Although not shown in the sketch, there is in practice a number of bolts passing through these two sets of molds at various places to hold them together in their relative positions. In the open space between the molds there are placed steel rods for the purpose of reinforcement; while all through the entire structure provision is made for water and steam pipes, gas-pipes and electric-light wires being placed in appropriate positions as the molds are assembled.
At the centre of the roof there will be noted a funnel-shaped opening. Into this there is delivered by the endless chain of buckets shown on the left a continuous stream of a special free-flowing concrete mixture. This mixture descends by gravity, and gradually fills the entire space between the two sets of molds. The delivery of the material—or "pouring," as it is called—is continued until every part of the space is filled and the mixture is even with the tip of the roof, thus completing the pouring, or casting, of the house. In a few days afterward the concrete will have hardened sufficiently to allow the molds to be taken away leaving an entire house, from cellar floor to the peak of the roof, complete in all its parts, even to mantels and picture molding, and requiring only windows and doors, plumbing, heating, and lighting fixtures to make it ready for habitation.
In the above sketch the concrete mixers, A, B, are driven by the electric motor, C. As the material is mixed it descends into the tank, D, and flows through a trough into a lower tank, E, in which it is constantly stirred, and from which it is taken by the endless chain of buckets and dumped into the funnel-shaped opening at the top of the molds, as above described.
The molds are made of cast-iron in sections of such size and weight as will be most convenient for handling, mostly in pieces not exceeding two by four feet in rectangular dimensions. The subjoined sketch shows an exterior view of several of these molds as they appear when bolted together, the intersecting central portions representing ribs, which are included as part of the casting for purposes of strength and rigidity.
The molds represented above are those for straight work, such as walls and floors. Those intended for stairways, eaves, cornices, windows, doorways, etc., are much more complicated in design, although the same general principles are employed in their construction.
While the philosophy of pouring or casting a complete house in its entirety is apparently quite simple, the development of the engineering and mechanical questions involves the solution of a vast number of most intricate and complicated problems covering not only the building as a whole, but its numerous parts, down to the minutest detail. Safety, convenience, duration, and the practical impossibility of altering a one-piece solid dwelling are questions that must be met before its construction, and therefore Edison has proceeded calmly on his way toward the goal he has ever had clearly in mind, with utter indifference to the criticisms and jeers of those who, as "experts," have professed positive knowledge of the impossibility of his carrying out this daring scheme.