The action of iron had been recognised for some time. Rottier mentions an experiment made with chips of wood impregnated with solutions of copper sulphate containing sulphate of iron in various proportions, and buried in the ground. The results showed - (1) that the ferrous sulphate had a certain antiseptic action, but much weaker than that of the copper; (2) that the duration of woods prepared with sulphate of copper solutions containing ferrous sulphate in varying proportions was nearly equal, except where the ferrous sulphate was present in very large proportion; (3) that for preserving wood, chemically pure copper sulphate offered no advantages over common commercial sulphate. The last conclusion is opposed to the view taken by Boucherie and other specialists. Rottier cites, in support of his opinions, the observations of Layen on an ancient wheel found in the copper mines of Sao Domingo, in Portugal. This wheel was in a perfect state of preservation, although it had been for 1400 years in water containing not only the sulphates of copper and iron, but notable quantities of the sub-sulphates of these metals.
Certain salts have an injurious action on wood impregnated with copper sulphate. If chips of wood so prepared are placed in a solution of chloride of lime, carbonate of soda, or carbonate of potash, the solutions will be found after a while to contain considerable quantities of copper sulphate abstracted from the wood. This shows that timber so prepared is unsuited for marine constructions. It explains, too, why such wood is liable to decay when employed in tunnels or in certain soils, as those containing much lime. The salts (as bicarbonate of lime, etc.) present in the water carry off the copper from the wood.
In certain soils carbonic acid will also abstract the copper. This may be shown by placing chips impregnated with copper sulphate in aerated water.
Rottier has endeavoured to prolong the duration of the wood by increasing the proportion of metal fixed in the ligneous fibre. Here it is necessary to have recourse to special modes of procedure, as when the wood is simply laid in a solution of the sulphate, the proportion of the latter, which becomes fixed, is pretty nearly constant and very small. He has found also - (1) That acetate of copper enables us to double the quantity of copper fixed. (2) Heating the wood also augments the quantity of copper fixed. (3) Certain organic substances have the same effect, acting on the ligneous fibre much in the same way as do mordants in dyeing processes. The effects of indigo and catechu in this respect are very remarkable. (4) The use of cuprammo-nium salts permits a much larger quantity of copper to be introduced into the wood. Experiments with shavings impregnated in various ways, and buried in a cesspool, proved that the durability was greater in proportion as the amount of copper fixed was larger. .Acetate of copper and indigo are too uncertain for general use. The effects of heat are not so reliable. Catechu. fan only be employed to a limited extent.
Cupram-monium salts, on the other hand, admit of general application, and the trifling increase in prime cost would be more than compensated by the longer duration of the wood. (Revue Tndust.)
Timber thoroughly well seasoned is in that condition in which its good qualities will be preserved, so that in one sense the seasoning and preservation of timber may be taken as the same terms. But timber may be well seasoned, and yet we may place it in such unfavourable conditions that it loses the good properties it may possess, and begins to decay. The term " seasoning "therefore may be accepted as indicating the process by which we give timber good qualities, that of " preservation," the process or means adopted by which we retain in it those properties. The oldest and most generally adopted method of seasoning timber, is steeping or immersing it in water. This is based upon the fact that by placing the timber in water, the sap is washed out of the pores and the water takes its place, which, when the timber is afterwards exposed to the atmosphere, is much more easily and quickly expelled by evaporation from the timber, than the sap in the ordinary or natural condition. To obtain the best results of this mode of seasoning in the quickest way, two things are essential; the water must be running water, and it must be as pure as possible.
Natural seasoning is simply exposing the timber to the air under sheds, or otherwise piled up. (Pract Mag.)
(6) To Preserve Woodworks That Are Exposed To Damp
(a) For those of an extensive nature, such as bridges, etc. The Hollanders use for the preservation of their sluices and floodgates, drawbridges and other huge beams of timber exposed to the sun and constant changes of the atmosphere, a certain mixture of pitch and tar, upon which they strew small pieces of shell broken finely - almost to a powder - and mixed with sea-sand, and the scales of on, small and sifted,which incrusts and preserves it effectual ly. (6) A paint composed of sub-sulphate of iron (the refuse of the copperas pans), ground up with amy common oil and thinned with coal-tar oil, having a little pitch dissolved in it, is flexible, and impervious to moisture, (c) Linseed-oil and tar, in equal parts, well boiled together, and used while boiling, rubbed plentifully over the work while hot, after being scorched all over by wood burnt under it, strikes 1/2 in. or more into the wood, closes the pores, and makes it hard and durable either under or out of water, (d) For fences and similar works, a coating of coal-tar, sanded over; or boil together 1 gal. coal-tar and 2 1/2 lb. white copperas, and lay it on hot. (7) To prevent rot. - (a) Thoroughly season the wood before fixing, and when fixed, have a proper ventilation all round it. (6) Charring, after seasoning, will fortify timber against infection; so will a coating of coal-tar. (8) To cure incipient dry rot. - (a) If very much infected, remove the timber, and replace with new. (6) A pure solution of corrosive sublimate in water, in the proportion of 1 oz. to 1 gal., used hot, is considered a very effectual wash, (c) A solution of sulphate of copper, 1/2 lb. per gal. of water, laid on hot. (d) A strong solution of sulphate of iron; this is not so good as sulphate of copper, (e) A strong solution of sulphates of iron and copper in equal parts, 1/2 lb. of the sulphates to 1 1/2 gal. water. (f) Paraffin oil, the commonest and cheapest naphtha and oil, or a little resinous matter dissolved and mixed with oil, will stay the wet rot. (g) Remove the parts affected, and wash with dilute sulphuric acid the remaining woodwork. (A) Dissolve 1 lb. sulphate of copper in 1 gal. boiling water, then add 1 1/4 lb. sulphuric acid in 6 gal. water, and apply hot. (9) To prevent worms in timber. - (a) Anointing with an oil produced by the immersion of sulphur in aquafortis (nitric acid) distilled to dryness, and exposed to dissolve in the air. (6)' Soaking in an infusion of quassia renders the wood bitter, (c) Creosoting timber, if the smell is not objectionable, (d) Anointing the timber with oil of spike, juniper, or turpentine, is efficacious in some degree. (e) For small articles, cover freely with copal varnish in linseed-oil. (10) To prevent worms in marine building.- - (a) A mixture of lime, sulphur, and colocynth with pitch. (6) Saturating the pores with coal-tar, either alone or after a solution of corrosive sublimate has been soaked and dried into the wood, (c) Sheathing with thin copper over tarred felt is esteemed the best protection for the bottoms of ships for all marine animals; the joints should be stopped with tarred oakum, (d) Studding the parts under water with short broad-headed nails. (11) To destroy worms in carvings. - (a) Fumigate the wood with benzine. (6) Saturate the wood with a strong solution of corrosive sublimate; if used for carvings, the colour should be restored by ammonia, and then by a weak solution of hydrochloric acid; the holes may be stopped up with gum and gelatine, and a varnish of resin dissolved in spirits of wine should afterwards be applied to the surface, (c) Whale-oil and poisonous ointments have been found of service.