Marine Pests.-- The most destructive of these are the Trredo Navalis or ship worm and the Lirrenon'a Terebrans. The teredo narolis is worm-shaped, being from six inches to 14 inches in length and one-fourth of an inch in diameter it is of gelatinous nature and trans lucent. Its head is provided with calcareous substance or shell in two parts working on a binge which performs the office of an auger. The head, like the body, completely fills the cavity bored and the outward appearance of the pile attacked shows no indication of the de struction going on within. Having once en tered the timber it never works out nor will one cross another hole although they are some times less than one-thirty-second of an inch apart, or from the surface. The teredo enters the timber at the ground level and works up ward, generally about two feet above low water, although it will attack floating timber; he wooden floats or buckets of a ferry steamer making half-hour trips for IR hours at a stretch and almost constantly in motion, have been completely hollowed by the tredo. It was a theory at one time that the hark on a pile was a protection against the teredo. While this is true to a certain extent, piles taken from some of the old wharves in San Francisco Bay have been found badly eaten by these worms. the bark being otherwise intact. The Um noria terebrans resembles a wood louse in appearance. It is about the form and size of a grain of wheat; it works between high and low water and is very destructive. It completely destroys the pile between the tide lines avoid ing all metal fastenings and knots in the wood The borings are so close together that the wood is completely disintegrated; ends and joints of timbers seem to he the most favorable points of attack. The protection of piles and timbers from these marine pests has been the study of engineers and scientists for many years and millions have been expended on experiments with varying success. In the direct preservation of piles proper, two methods have been followed. The first and longest in use is impregnating it with chemicals that are destructive to animal life and the second is by covering the pile with an insoluble armor or artificial bark impervious to the worms.
Cresoting.— Without doubt the creosoting process is the most valuable and efficient of all processes known for prolonging the life of tim ber. The process was invented in England about the same time that kyanizing and the other metallic salt antiseptics came into use; it has survived all other processes and is used to a greater extent than any other method both in Europe and this country. The creosote is de rived from the destructive distillation of wood and coal and consists of oil products designated as dead oil when derived from the distillation of coal or coal tar and wood creosote oil when derived from the distillation of wood or wood tar. The dead oil contains naphthaline, phenic or carbolic acid and other powerful antiseptics which change the chemical nature of the sap by forming therewith soluble compounds while the naphthaline rendered sufficiently fluid by prelim inary heating, enters the wood cells, solidifies and becomes permanently fixed, mechanically coating and protecting the fibres against forma tion of fungi. The wood creosote contains par affine, pyroligneous acid and other antiseptics. The advantages claimed for this oil are that its penetrating power is much greater and,it is less expensive than dead oil and is equal)' soluble in water. The limited use of this oil seems to con firm these claimed advantages, but the matter cannot he considered conclusive until more defi nitely established by further experience and the test of time. All experts on preservation of tim ber agree that the density of timber must be favorable to impregnation; in other words, only open-pored timbers should he used for treat ment with creosote, this having the least liquid ity and, therefore, the hardest of all preserv ative chemicals to force into and thoroughly impregnate the wood. The Oregon pine or
yellow fir used on the Pacific Coast is con sidered too dense to permit a thorough im pregnation and if treated with creosote requires a longer steaming and a greater heat to extract the sap and open the pores and also a'greater pressure to force the material into the wood The consequences therefrom have been check ing and cracking the timber, making it brittle and when used for piles the process has cracked them so extensively that the limnoria were found in and behind these cracks in sheltered places in which it has done its destructive work under cover and more rapidly than when ex posed to swell and current It has also made examination of those piles more difficult, as the outer shell of the pile was apparently unat tacked while the inner portion of the same was entered and destroyed by the limnoria. All authorities in writing on the preservation of piles for marine work seem to ignore the ex istence of the limnoria terebrons. In my opinion it is much more destructive on the Pacific Coast than is the teredo, and while a pile that has been thoroughly creosoted will resist the teredo, even if somewhat checked, the limnoria will find the slightest opening and destroy the pile. There have been several methods for the preservation of piles in San Francisco Harbor by means of an exterior covering or artificial bark, some of which have been more or less successful, the success depending upon the dura bility of the covering, or, in other words, the life of the pile is the life of the artificial bark. The one making the best showing, from the fact that it has been the longest in use, is the paraf fine method. It consists of a surface of paraf fin paint, covered with battens which have been treated with the paint The secret of the success of this process is the fact that it is applied cold. Previous coverings of this char acter having been applied hot to a wet pile, no adhesion was obtained between covering and the pile for the reason that the hot material draws the moisture to the surface. This tiffi culty claims to have been avoided by the parties kiln-drying the piles before covering This process consists in covering the piles spirally with a double thickness of burlap treated with asphalt, the application or winding of the burlap being done by means of a large lathe in whirl the piles are turned. Another protection against these marine pests is a pile built up from a core of 6 X 6 with one-inch boards until it is 12 inches square, each layer being tarred and sanded. It is built on the theory that the teredo is loath to cross a seam and the test pile taken from section I of the seawall, a par ticular feeding ground of the teredo, after 10 years' immersion, verified this theory But this was a case of again ignoring the ever active limnoria, and piles built since have shown that the limnoria found a home in the seams of the boards of which the pile was constructed. An improvement was made in the details of construction which has resulted in keeping the linmoria out and that was the placing of ship felt between the last two layers of boards from high water to two feet below low water (lim norm working only between high and low water). In many of the government piers where the teredo and limnona are particularly active, numerous iron piles have both wrought and cast. These are prohibitory in many places by reason of excessive cost of the material and construction, most of the piles having either to be screwed into the bottom or driven with a water jet. Another objection is the rapid destruction by oxidization of the joints in the bracing system.