(8) The results of some experiments on the preservation of sheet-iron used in railroad bridges have been published by the directory of the Government railroads of the Netherlands. From 32 sheets half was cleaned by immersion for 24 hours in diluted hydrochloric acid; they were then neutralised with milk of lime, washed with hot water, and while warm, dried and washed with oil. The other half was only cleaned mechanically by scratching and brushing. 4 of each kind were then equally painted with red-lead, with 2 kinds of a red paint of oxide of iron, and with coal-tar. The plates were then exposed to the weather, and examined after 3 years. The result was - (a) That the red-lead had kept perfectly on both kinds of plates, so that it was impossible to say if the chemical cleaning was of any use. (6) That one kind of iron oxide red paint had better results on the chemically-treated plate than on the other - in fact, a result equal to that of the plate painted with red-lead; while the other kind of iron oxide red gave not very good results on the plates when only scratched and brushed, (c) That the coal-tar was considerably worse than the paint and had even entirely disappeared from those iron sheets which had not been treated chemically, but only cleaned by brushing. (Eng, . Mech.)
(9) Oast-Iron Pipes
The water from mines frequently contains enough acid to attack cast-iron pipes, destroying them in a short time. Oil colours and varnishes offer but a limited resistance, and the process of enamelling employed in Oberschlesia,says Engelhardt of Ibbenburen, although permanent and effective, is expensive. Cement is cheaper, and is unacted upon by these waters, and the only question to be settled was whether it would adhere to the smooth iron with sufficient firmness. Two similar pieces of rolled iron were taken, and one of them painted over 5 times with a very thin cement, so that the coating was 1/5 in. thick. Both pieces were suspended near together in that part of the shaft where the water had attacked the signal cable most violently, and were left there 4 months. On taking them out, the unprotected iron was found to be reduced to 1/3 its original thickness; the other, in which a hole had been bored to suspend it, had suffered the same corrosion at the exposed portion; the cement covering was dark brown, but perfectly hard and unattacked by the acid. The cement was broken off, and the surface of the iron exhibited the dark-blue colour and lustre that it had on leaving the rolls.
As this coating adhered so well to the smooth rolled iron, to which it cannot cling so tightly as to the rougher" surface of cast iron, the experiment was continued on a larger scale. A 26-in. discharge pipe in the Oeyhausen shaft was protected on the inside with cement. The coating remained unchanged for 2 years, while the pump was in constant operation. At the beginning of last winter, the pump was stopped, and the pipe being no longer under water, the cement was so much injured by the frost that it scaled off. Several other experiments were made with similar results. The pipes should be new, or, if old, well' cleaned from rust before applying the cement, which is mixed as thin as is possible without injury to its tenacity. The pipe is moistened before the cement is applied, a thin coating of cement is put on and allowed to dry; when hard, it is moistened, and a second coating is applied; and so on 4 or 5 times. The operation cannot be conducted so well in very hot weather, as the cement dries too quickly; nor must the pipes be exposed to frost during the operation or afterward.
This unfortunate sensitiveness to cold may perhaps yet be overcome by interposing some semi-clastic material between the iron and cement. (Iron.)
(10) Dr. W, H. Sterling's process consists in the impregnation and saturation of the structure of the metal with a non-oxidising or non-oxidisable substance, by forcing it into the intercellular spaces of the metal by pressure while the iron is in an expanded condition, induced by heating. He gives one method by which his invention may be applied, and which he recommends as being eminently practical and useful. A vessel of any suitable material, of sufficient strength, is made in the form and size best adapted to those of the iron article to be treated, with the lid so constructed that the vessel may be closed hermetically; at the bottom, pipes are arranged for conveying steam and water alternately, for the purpose of heating and cooling the interior. Connected with this vessel is a force-pump, for producing the necessary pressure, and appliances for obtaining a vacuum. The iron to be treated is heated to the desired temperature, placed in the-above vessel, the top is closed hermetically, and dry or superheated steam is turned into the pipes at the bottom, to keep the metal at the required temperature; also, at the same time, an atmospheric vacuum is produced by an ordinary air-pump connected with the chamber; the proper quantity, sufficient to fill the vessel, of pure paraffin or paraffin in solution with one of the pure mineral oils, having been also previously heated to the required temperature, is now let into this chamber and forced under pressure into the intercellular spaces of the iron, those having so enlarged by the expansion of the metal from the heat and removal of the atmospheric pressure as to' readily admit the hydrocarbon preservative.
When the iron has remained under this liquid pressure a sufficient time, it is gradually cooled by turning cold water instead of steam into the pipes, the pressure being kept up, however, until the iron is cool. Certain qualities of iron may be treated without the atmospheric vacuum, but as the iron expands very much more, while greater pressure is obtainable by its employment, and the additional cost is not to be considered he recommends its use as desirable. (Van Nostrand's Magazine.)
(11) To preserve iron from oxidation when exposed to the air, Keigelmann takes the ordinary paints made up of boiled linseed-oil and the oxides of the heavy metals, and incorporates therewith in' the cold about 10 per cent, of calcined magnesia, baryta, or strontia, which has been previously steeped in an equal weight of light mineral oil. To preserve iron from rusting in the earth, as, for instance, gas or water pipes, water tanks, the sides of iron ships, etc, he melts 100 parts rosin and 25 of gutta-percha in 50 of paraffin; this resinous compound is then stirred into mineral oil, so as to have the consistence of paint, with which are then incorporated in the cold 20 parts calcined magnesia. In place of magnesia, equal weights of caustic baryta may be added, according to circumstances. After the addition of the magnesia, the mixture is anew diluted with mineral oil until it can be applied with a brush. To preserve pieces of polished machinery or other article of iron or steel, and to be able to guarantee them against rust during carriage, the coating is composed of vaseline, or of heavy mineral oils, with the addition of 20 to 30 per cent, of calcined magnesia.