Air-dried wood, under ordinary atmospheric temperatures, retains from 10 to 20 per cent of moisture, whereas kiln-dried wood may have no more than 5 per cent as it comes from the kiln. The exact figures for a given species depend in the first case upon the weather conditions, and in the second case upon the temperature in the kiln and the time during which the wood is exposed to it. When wood that has been kiln-dried is allowed to stand in the open, it apparently ceases to reabsorb moisture from the air before its moisture content equals that of wood which has merely been air-dried in the same place, and under the same conditions, in other words kiln-dried wood will not absorb as much moisture as air-dried wood under the same conditions. Difference between Seasoned and Unseasoned Wood Although it has been known for a long time that there is a marked difference in the length of life of seasoned and of unseasoned wood, the consumers of wood have shown very little interest in its seasoning, except for the purpose of doing away with the evils which result from checking, warping, and shrinking. For this purpose both kiln-drying and air-seasoning are largely in use. The drying of material is a subject which is extremely important to most industries, and in no industry is it of more importance than in the lumber trade. Timber drying means not only the extracting of so much water, but goes very deeply into the quality of the wood, its workability and its cell strength, etc. Kiln-drying, which dries the wood at a uniformly rapid rate by artificially heating it in inclosed rooms, has become a part of almost every woodworking industry, as without it the construction of the finished product would often be impossible. Nevertheless much unseasoned or imperfectly seasoned wood is used, as is evidenced by the frequent shrinkage and warping of the finished articles. This is explained to a certain extent by the fact that the manufacturer is often so hard pressed for his product that he is forced to send out an inferior article, which the consumer is willing to accept in that condition rather than to wait several weeks or months for an article made up of thoroughly seasoned material, and also that dry kilns are at present constructed and operated largely without thoroughgoing system.