The first attempts at artificial drying did not contemplate general stock or drying lumber for shipping, the first dry-houses being usually nothing more than a one-story frame structure built over a low cellar excavated in the side of a hill, with a slatted floor above and a latticed cupola on the roof. A brick or tile furnace or arch was built in the cellar, from which extended a number of sheet-iron pipes which, while conveying the smoke to the chimney, also acted as radiators. The furnaces were built so as to be stoked from the outside through an arch in the wall on the down-hill side. After the introduction of cast-iron stoves, they were often substituted for the brick or tile furnaces, and in some cases these in turn were superseded by wrought-iron cylinders like steam-boiler shells.
The material to be dried was stacked upon the slatted floor in loose piles, through which the heated air from below could circulate more or less freely. For years these dry-houses—they were not then dignified by the name of kilns—were only used in connection with certain manufactories for drying stock already cut up for tubs, pails, and other wooden ware; small boxes, chairs, and other furniture material; turned work and Yankee-notion stock in general; no regular lumber stock being subjected to the process.
These dry-houses contained such an element of fire risk that they were generally built in isolated positions as close to water as possible. Even then they were a constant menace to all surrounding property as well as to their own contents. Lumber, except in small pieces, dried in them was apt to be checked and warped or twisted more or less, and was not at all satisfactory save in the one feature of being free from moisture.
The fire risk at last became so great where the establishments requiring the dry-houses were situated in towns, and the restrictions of underwriters so onerous, that along in the fifties some crude attempts were made to substitute steam for the furnaces by conducting the exhaust from the engines running the works into the cellars.
It is not definitely known when or by whom the first attempts were made, but it is a fact that as early as 1855 the trial was made by a manufacturer in northern Massachusetts
The physiology of wood, or what is now known as timber physics, was poorly understood by any one, much less by the men who were making the experiments; for in general they were plain business men, with only ordinary business education, and with no pretensions to scientific knowledge.
Thus little or nothing was known of the chemistry of woods and absolutely nothing of the effect of heat upon the gums, juices, or fibers. But while these men were not up in the sciences, they possessed what perhaps in this instance stood them in as good stead—hard common sense and quick perceptions, that permitted them to learn rapidly by experience and by quickness of observation to note the results upon the woods of various conditions in the course of their experiments.
It had probably always been known that lumber would dry, and did dry, most rapidly during the season of high winds, but the fact had been generally accepted without asking for a scientific reason. But when it dawned upon the minds of the experimenters that there must be one, it led to the further discovery that air in motion of a low temperature would produce better results than air of a high temperature if kept stagnant, and that the ordinary atmosphere, with its natural temperature, if above the freezing point and with a low degree of humidity, if kept in constant motion or circulation, would dry lumber well and rapidly without the aid of artificial heat.
These points once definitely settled and understood, led to researches that immediately led into the domain of wood chemistry and physiology, and the experimenters and inventors became to a degree chemists and physicists. Thus a special education was obtained before they were able to say they had solved the problem of drying lumber artificially; fairly accurate knowledge on the following points being gained:
1. (a) Different varieties of wood, and (b) wood of the same variety grown in different localities, requiring radically different treatment.
2. (a) That too high a degree of heat applied at any stage, and (b) especially during the first, injured the lumber more or less, according to kind, and retarded or prevented perfect drying.
3. That with a perfect circulation of air of a low degree of humidity, a high temperature was not necessary to produce good results except as to time.
4. That the results, good or bad, depended very largely upon the chemical changes produced by heat upon the natural gums and juices of the wood.
5. That all these points became much more pronounced in the case of hard woods, and hence the necessity for special machinery and arrangement of the kiln.
The modern day kilns bear no resemblance to the old ones. Nowadays, they are usually constructed out of aluminium or steel and have a range of sophisticated systems used to carefully control airflow, temperature and humidity levels. Like most modern inventions, these systems are governed by computers.
Log World is dedicated to supplying responsibly sourced firewood, all of our timber comes directly from arisings produced by our sister company Hedges N Trees - A firm of skilled tree surgeons with the highest of reputations in the Surrey area.
As suppliers of locally sourced and recycled timber we do not contribute to any destructive forestry clearance operations.