ON AMERICAN PERMANENT WAT. 599 



service, do not absorb a preservative solution as readily as the softer and 

 inferior kinds, which latter wear out very rapidly, and the cost of using a 

 preservative would only be a useless expense. 



On roads with very light traffic, operated by horse-power, as street 

 railways, longitudinal timbers placed under the rails have been generally 

 used as supports, those for the same track being tied across at intervals 

 to preserve the gauge of track. This arrangement, however, will not 

 answer for locomotive traffic ; and even for street railways, as already inti- 

 mated by the author, it is being abandoned, a form of rail being adopted 

 that will admit of the use of cross ties. A longitudinal sleeper is very apt 

 to split with the spikes which must be driven into it at frequent intervals 

 in its length to hold the rail, water gets into these cracks, softening and 

 decaying the timber, and there is a great tendency in the rail to sink into 

 the wood, the supporting power being lost. Timber will always bear 

 a load best resting across the grain, even when in first-class condition ; 

 the cross- tie system also offers great advantages in renewals over the 

 longitudinal stringer system, vastly increasing facilities of replacing 

 material without delay or interruption of traffic. Even on bridges 

 whei'e longitudinal stringers have been used for years, on account of 

 advantages obtained in the details of construction of the floor system,, 

 they are now being abandoned and a cross-tie system adopted. The 

 rationale of the present almost universal method of timber cross-tie 

 supports is therefore readily seen. 



These ties are placed at frequent intervals, sufficient to properly 

 support the rails, the latter being securely spiked to them, and the ties, 

 in addition to giving the proper support, tie the rails together to gauge, 

 and by their hold in the ballast below, keep the whole track in line. 

 Hence the American word ' cross-tie,' at once descriptive and appropriate. 

 The cross-tie should, if possible, be of what is technically termed ' hard 

 wood,' and of all woods in America the best for this purpose is white oak. 

 This is the case at least in the temperate zone. There may be some woods 

 in the tropics, unknown to the author, that are better. 



The more bearing surface the rail has on the tie, and the more surface 

 the tie has on the ballasting material below it, the better and more stable the 

 track. Hence the ties should be flattened on the upper and lower sides, and 

 a minimum width of flat surface should be specified, less than which will 

 not be allowed. The sides of the ties are only barked and left rounding. 

 Sawed ties are sometimes used cut square on all sides, but hewn ties are 

 by far the best, less liable to decay, and giving a better shape with the 

 rounded sides. The length of the tie should be sufficient to give ample 

 allowance outside of each rail and all the requisite bearing surface on the 

 ballast below. Hard-wood ties not only carry the rails better than soft 

 wood, but they will also hold the spikes two or three times as firmly. In 

 soft wood the spike bruises and breaks the fibres, while in hard wood it 

 tends to compress and push them back on themselves, increasing the 

 pressure against the sides of the spike and holding it tighter. The great 

 scarcity of hard woods in some sections necessitates, however, the use of 

 softer and inferior material — hemlock, spruce, the various kinds of pine, 

 &c. — and hemlock in particular is used in large quantities, being very 

 abundantly distributed over the country, notwithstanding that it is one 

 of the poorest woods for the purpose, and liable to very rapid and decep- 

 tive decay, the interior going first, leaving only a hollow shell of good 

 timber outside. 



