The following statement shows the results of some inter esting experiments on the cohesive strength of bar-iron, as detailed in an American publication :— " The mean result of numerous experiments on wrought iron, detailed in the JOIll'aul of the Franklin Institute, made by a Committee of the Institute, at the request of the Trea sury Department of the United "The experiments were male at ordinary temperatures on bars of iron averaging 1 inch by inch." To preserve, iron from rust, particularly when polished, various methods have been tried with more or less success: among others. the partial oxidation, known by the term blueing, has been adopted : the slightest coat of grease is sufficient to prevent rust.
'With to this subject. more especially as to the efThet of sea-water on cast-iron, :Air. Faraday addressed the followinr observations to Sir 11yain Martin, chairman of the " Harbours of Reffige :mil Defence" c(minlission : " Sir,-1 hasten to reply to your note. though not, I fear, with any certain knowledge: for infirm health has prevented me from taking up the consideration of the action of sea-water on iron, as my observations will permit. I conclude that the • question is of cast-iron in sea-water. Between these two bodies, there is a vigorous action. As far as I have been able to observe, it is the greatest in the water near the sur less in deep water ; and least of all the iron is buried in sand, or earth, or building-materials (into which the water may penetrate ;) for then the oxide and other results tbrmed, are detained More or less, and form sometimes a cement to the surrounding matter, and always a partial protection. Soft cast inn:, as for as my experience goes (which is not touch,) corrodes more rapidly than hard cast ; soft cast-iron. as far as my experience goes, more rapidly than the brittle white iron. As to the amount of col rosiun in any given time, I have not had the opportunity of observing any good and satisffictory cases of illustration.
" In estuaries and the months of rivers, it is very probable that great differences of corrosion will arise from the different circumstances aariable saltness; the soil of the river, if' near a town, the metallic will mueh affect it, thus a wharf of cast iron might occasionally be greatly injured by making fast to it vessels that are coppered, using iron cables.
" As to the protection of iron, and first by a coating; the permanency °fa coat of paint, or of tor, or bituminous matter, can only be ascertained by reference to experience. Of this
I have none, except in a ease where coated iron sheathed for was brought to me. I was much impressed with the thorough adhesion of the coat to the iron. The process was patent, and I cannot remember whose it was. Zinced iron would no doubt resist the action of the sea-water as long as the surffice was covered with zinc, or even when partially crusted with that metal ; but zinc dissolves rapidly in sea water, and after it is gone, the iron would follow, "As to voltaic protection, it has often struck ine that the cast-iron piles proposed for light-houses, or beacons. might be protected by zinc, in the manlier Davy proposed to protect copper by iron ; but there is no doubt the corrosion of the zinc would be very rapid. If found not too expensive, the object would be to apply the zinc protectors in a place where they could be examined often, and replace them when ren dered inelli_•ctive. In this manner, I have little doubt that iron could be protected in our sea-water. It is even probable that, by investigation and trial, different sorts of iron might easily be distinguished and prepared, one of which would protect the other ; thus soft cast-iron would, probably, p•o teet hard cast-iron, and then it would be easy to place the protecting masses where they could be removed when required.
•• Ilenee, though iron be a body very subject to the action of sea-water, it does not seem unlikely that it might be used with advantage in marine constructions intended to be per manent, if the joint effects of preserving coats of voltaic protectors were applied. Perhaps engineers are in the possession of practical and experimental data sufficient to allow the formations of a safe judgment on this point. For my own part, I am not, and therefiire am constrained to express the above opinions with much doubt and reserve." Iron is the most useful and most plentiful ofall metals. It requires a very intense heat to fuse it, on which account it can only be brought into the shape of tools and utensils by ham mering: this high degree of infusibility would prevent the uniting of several masses into one. w ere it not from its being capable of welding, a property found in no other metal, except platina. In a white heat, iron appears as if covered with a kind of varnish: and in this state, it' to pieces be applied together, they will adhere, and may be peifectly united by forging.