The success of creosoting depends almost entirely upon the effectual seasoning of the timber. Only a very small quantity of creosote can be forced into wet or unseasoned sleepers, even with the best machinery and exceptionally high pressures, while a thoroughly dry sleeper will 213 readily absorb from 2⅓ to 3 gallons. More could be forced into the dry sleeper if necessary, but a little consideration will show there would be no advantage in doing so. In railway sleepers there are two elements of destruction at work--one the decay of the timber, and the other abrasion or wearing away of the wood itself from the constant pounding of the passing loads. More particularly does this wearing-away take place with the flange, or bridge, rails, their distributed bearing surface on the sleeper being less than the cast-iron chairs. A thoroughly well-creosoted 5-inch sleeper laid originally with a thickness of 4-¾ inches in the centre of rail-seat, as in Fig. 306, will wear down 1½ inches, the timber remaining quite sound. The writer has had to take out thousands of sleepers where the seats of the flange, or bridge, rails had been pounded or worn down so deep into the wood as to leave too small a thickness of timber to carry the rail with safety. These sleepers had to be taken out of the road, not on account of decay, but because they were actually worn down too thin to be of service. They had done their work well for a long series of years, and were perfectly sound when taken out. No increased quantity of creosote would have made them last longer, and any increased quantity of creosote would have been waste. Two and three quarter gallons of creosote is a very good and suitable quantity for a 10 inch by 5 inch rectangular sleeper, but not more than half this quantity can be forced in if the sleeper is wet or unseasoned.