This is a subject of much consequence on account of the great number of wooden structures in our country, and the serious accidents from the conflagration of steamboats and buildings which take place so frequently. Various substances have been employed to coat wood so as to render it incombustible. Alum, lime and clay, in solutions, have been the most common and the cheapest substances applied to such purposes, but not with that success which is desirable. The attention of our steamboat inspectors has often been directed to this question, Trat, sofaras we have been informed, no experiments have either been devised or conducted by them for shedding light upon it. In recent numbers of the London Mechanics' Magazine, we find some very useful information connected with this subject, which we know will be very useful and interesting to our readers. It was proposed by Mr. Abel to pay the timber beams and bulkheads of ships with a solution of the silicate of soda to render them partially, at least, if not perfectly incombustible, to check the progress of fire in cases of conflagration in vessels. Specimens of wood thus prepared at Portsmouth, England, were submitted to the action of fire conjointly with unprepared timber, and it was found that while unprepared wood of the same dimensions and character burned rapidly away under intense heat, that prepared with the silicate solution smoldered very slowly. The silicate seemed to fuse and cling to the surface of the wood under fire, and thus protect it. Those who conducted these experiments were satisfied that wood coated with the silicate of soda, and used for beams, bulkheads, or the undersides of decks and sides of vessels, would not be liable to take fire ; and if the cargoes of vessels, with timbers so prepared, should take fire, it would be easy to confine the conflagration to the spot where it commenced, and secure time for efforts to suppress it. A slight application of lime-wash to wood affords some protection from fire, so does a coating of clay, but these are liable to scale off, and are therefore not suitable. A process was lately patented in England, by E. Maughann, for securing this object. It consists in saturating dried wood with an aqueous solution of the phosphate of soda and muriate, or sulphate of ammonia. The patentee thinks that when wood prepared with these substances is submitted to the action of fire, such a quantity of vapor will be generated by the ammoniacal salts as will extinguish the fire. Another patent process was that of Lieut. Jackson, and consisted in impregnating the wood with solutions of the salts of zinc and ammonia. The wood was prepared by these solutions in large cylinders, the air exhausted, and the liquid forced in under a pres* sure of 150 pounds on the square inch, which was maintained for two hours before the timber was ready to be taken out. Brunei, the designer of the Leviathan, tested seventeen different kinds of wood prepared by Lieut. Jackson's process, and it was found that they all withstood the action of fire in a superior manner to unprepared or painted wood. Both of these processes are expensive, however, and when the solutions are strong, they tend to injure the strength of the timber. A wooden hut having been erected in the Woolwich Marshes to test the value of Phillip's fire annihilator, it occurred to Mr. Abel to test the value of the silicate of soda; also, a solution of lime and alum, as fire protec-tives, and some of the timbers of the hut were therefore washed on the surface with these solutions. The alum and lime solution was of little avail, and the annihilators failed to extinguish the fire, but the planks treated with the silicate of soda greatly retarded the fire, as they did not blaze, and presented merely a charred appearance by the intense heat. After this experiment, it was suggested that, in order to render the application of the silicate of soda less expensive, the wood should receive a primary coating of the silicate applied with a brush ; then, when dried, a coating of common lime whitewash and dried, and afterwards a finishing coating of the silicate of soda, somewhat stronger than the first one. Wood thus prepared was submitted to a great variety of tests with decided success. The protective coating resisted the action of fire to a remarkable degree, and did not scale off; and when exposed to the action of a stream of water, it could not be washed off. Upon the result of these tests being reported, an order was issued by Lord Panmure to make further and more perfect experiments at Chatham, under the direction of Col. Sandham and Mr. Abel, to determine practically and fully the value of the silicate of potash and lime wash, as described, to protect wood from fire. The experiments were made, and Col. Sand-ham and Mr. Abel conducted them, and they have reported the results. That report, in substance, states that the silicate of soda, in conjunction with lime wash, applied to the surface of wood with a brush, affords great safety to wooden structures in cases of fire. It is not a perfect protective, as this result, cannot be expected, but it is a cheap and good safeguard, and they recommend its use by government. The cost of the silicate for the purpose described was only about four cents for coating a surface of ten square feet. It was applied in the form of thick sirup, the lime-wash was about the thickness of cream, and the last coat of the silicate was a little stronger than the first. The surface of the wood to which it is applied must be free from paint or grease, and care must be exercised not to put on the lime too thick, because it will then be liable to crack off. This is a subject to which we wish to direct the special attention of our engineers and 'architects. Very frequent conflagrations take place on the Mississippi river steamers, many of which may be prevented, or at least saved from the disastrous results generally attending them, by the use of this method of coating the inside of their timbers.