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Professor C. F. Chandler, of Columbia College, New York, in a letter dated March 14, 1868, says :

Numerous processes have been invented for protecting timber from decay, some of which have been found to be very effective. The great expense of several of the proposed materials bas prevented their general use, however, and in practice the “dead oil” of coal tar has been found to satisfy most fully the two important requirements of effectiveness aud cheapness.

The use of this material was patented in England in 1838, by Bethell, and the process has been very generally employed for railway sleepers, piles, &c., with the most satisfactory results.

Very recently, Professor Charles A. Seely, who has devoted considerable attention to the preparation of carbolic and cresylic acids from “dead oil," for disinfecting and antiseptic purposes, bas materially improved the English process. In Bethell's process the timber is placed in wrought-iron cylinders, from which the air is then partially exhausted by pumping machinery; the oil, at a temperature of 120° Fahrenheit, is then admitted, and a pressure of 120 to 200 pounds per square inch is applied to force the oil into the pores of the wood.

This process requires seasoned wood and expensive machinery, and admits of two improvements, viz: the use of a more carefully prepared oil, and a cheaper and more effective impregnation of the timber. In the creosoting process of Professor Seely, I think both these improvements are secured.

Professor Seely employs an oil which is rich in the carbolic and cresylic acids, which are the most effective disinfecting and antiseptic agents known, as has been abundantly proved by the experiments made in Europe in connection with the cattle plague.

He also adopts a most simple, and at the same time effective method of impregnation, which does not require the expensive machinery necessary to produce the vacuum or the high pressure of 120 to 200 pounds per square inch, and which is executed in a few hours. That the wood is thoroughly impregnated is proved on boring into the very centre of the large blocks of the Stafford pavement, and subjecting the borings to the proper chemical • tests, by which the presence of the tar acids is ascertained.

I am satisfied, from a careful survey of the subject, that Professor Seely's process is a very decided improvement on the Bethell process, and that a pavement prepared by it will resist both wet and dry decay, and will actually contribute, by the effect of the materials with wbich it is saturated, to the disinfection of the street filth with which it must necessarily come in contact.

Professor J. S. Newberry, of New York, in a letter dated March 14, 1868, says :

The carbolizing process of Professor Seely to which this pavement is subjected, cannot fail to give it very positive advantages over any other in use, not only as imparting to the wood greater durability, but the antiseptic agent employed must exert a purifying influence on the emanations from, and the drainage through, the streets in which it is laid.

Though the Nicholson pavement is proved to be unexpectedly durable, and it is claimed for it that it will wear out before it will decay, still, in some especially well-drained surfaces, I have known the blocks to be affected with “dry rot."

It is at least true that there is a limit to the durability of wood not treated with any preservative preparation, and in the gutters and elsewhere, where the wear of the pavement is slight, that pavement is most economical which will longest resist the action of decay.

Professor Seely’s process for preserving wood permits the application of the best preservative agent known at least as thoroughly as any other, and very much more cheaply:

It is also applicable to green as well as dry wood, and to a cheap as well as to an expensive wood.

Professor Benjamin Silliman, of Yale College, in a letter dated New Haven, March 31, 1968, says:

Professor Seely's patent covers a process, believed to be new, of applying substances long known for their excellence in this particular to the preservation of timber. The substances thus employed are those produced from the distillation of coal tar, and known commercially as "dead oil,” containing carbolic acid or phenol. It is the last-named substance which possesses the remarkable antiseptic and disinfectant properties which give value to the “dead oil” as a preservative agent. The peculiar value of "dead oil” as a means of preserving timber bave been long known and appreciated. The “creosoting process," as it is called, has been for many years in use in Great Britain as applied to the preparation of railway ties and timber, and to piles for marine wharfs, and with great success. The process of Bethel is the one in general use there. Professor Seely's process claims, and I believe

deserves, an advantage in economy of time and in thoroughness. The samples of both soft and hard wood, which I have seen prepared by his method, are most thoroughly impregnated with the dead oil,” no portion of the fibre escaping saturation.

Phenol or carbolic acid exceeds all other known substances in its power of arresting and preventing decay, and the dead oil” contains, in addition to this remarkable body, a form of hydrocarbon which hardens on exposure, and being injected into the pores of the wood fills them, excluding both atmospheric oxygen and moisture, and finally solidifies the whole nto a resinous or pitch-like body almost incapable of decay. Beyond its antiseptic power, carholic acid or phenol possesses a specific poisonous power over the lower forms of vegetable life, fungi, &c., which are so active in promoting the decay of wood.

The action of “dead oil" as a means of preserving wood may be thus summed up, viz:

1. It coagulates albuminous substances and gives stability to the constituents of the cambium and cellulose of young wood.

2. It absorbs and appropriates the oxygen which is within the pores of the wood, and so checks or rather prevents the destruction of the woody fibre.

3. It resinifies within the pores of the wood and thus shuts out both air and water.

4. It acts as a positive poison to the lower forms of vegetable life, and so protects the wood from the attacks of fuugi and other parasites.

2d Session.

No. 271.

SURVEY OF TENNESSEE RIVER.

LETTER

FROM

THE SECRETARY OF WAR,

TRANSMITTING

Report of the surveys on the Tennessee river, made in compliance with the act

of March 2, 1867.

March 27, 1868.-Referred to the Committee on Commerce.

APRIL 30, 1868.-Ordered to be printed.

War DepaRTMENT,

Washington City, March 26, 1868. SIR : I have the honor to send herewith a communication of the 25th instant, from the Chief of Engineers, with a copy of a report by W. B. Gaw, civil engineer, of the examination and surveys on the Tennessee river, made in compliance with the provisions of the act of March 2, 1867. Your obedient servant,

EDWIN M. STANTON,

Secretary of War. Hon. Schuyler Colfax,

Speaker of the House of Representatives.

HEADQUARTERS CORPs of ENGINEERS,

Washington, D. C., March 25, 1868. Sir: In compliance with the provisions of the act of March 2, 1867, requiring examinations and surveys to be made at certain localities therein designated, I herewith transmit a report from Major and Brevet Major General G. Weitzel, corps of engineers, with an appendix thereto, containing a report in detail of the examinations and surveys on the Tennessee river, between Chattanooga and its mouth, made by W. B. Gaw, esq., civil engineer, under the direction and supervision of General Weitzel, with estimates of the probable cost of the various plans recommended for the removal of the obstacles to the navigation of the river.

The several plans presented for the complete improvement of the river involve an expenditure of more than $4,000,000.

They include, in addition to the removal of bars, ledges, and boulders, and the construction of wing and lateral walls, a canal of about 11 miles in length around Elk River shoals; another of 41 miles around the Little Muscle shoals;

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