While not as strong as steel pipe under hydrostatic test, many pipe users insist that, presumably on account of its slag enclosures and cinder films which are supposed by some to surround and protect the fibers, wrought iron pipe outlasts steel pipe when used under conditions which induce corrosion. Others are as strenuous in their denial of this assertion and this subject of comparative wrought iron pipe and steel-pipe corrosion is still a very live issue. For many years this matter has been under investigation. Hundreds of tests have been made and discussed by learned societies and their committees. The laboratories and testing departments, too, of the large pipe manufacturers and their customers, have made extended investigations. However, the conditions under which pipe is used are so varied and the time required for any true and decisive test is so long that really conclusive results have not been forthcoming. With other materials, each condition and corrosive influence is largely a “law unto itself,” and one wonders if such may not prove to be the case with these materials also. As suggested, a great quantity of published information giving comparative service tests is available for those who are particularly interested in this subject. How much of the decline in tonnage and in percentage of the total skelp produced, is due to the approximately 30% greater cost of wrought iron pipe and how much to satisfactory performance of its competitor must be left to you to judge. Fortunately pipe of both kinds is available, meanwhile, and one can get whichever he prefers. The uses of pipe are almost innumerable. Great quantities are used for conveyance of water, oils and gases, for ice-making and refrigeration, the heating and draining of buildings, for dry kilns, hospital beds and apparatus, electric light, railway and telegraph poles, pipe railings, for conduit work, etc. For many of these applications, the seamless variety is now utilized, however. For many purposes coated pipe is highly desirable. This may be by hot asphalt, or other liquid dip, by surface electro-galvanizing or by the hot galvanizing method of dipping in molten zinc, by which method probably the greater portion of coated pipe is treated. Certain other protective coatings are used to a limited extent. CHAPTER XXI THE MANUFACTURE OF SEAMLESS STEEL TUBES It is more than likely that the popularity of the bicycle, which created the recent great demand for strong, light and perfect tubes, was largely instrumental in developing the seamless tube industry, which may be said to have “sprung up” within the last twenty-five years. Previously all of the iron and steel pipes or tubes obtainable were either of the “butt” or “lap-weld” variety with the exception of those which were made from long pieces of metal by boring holes lengthwise through them. Tubes by this boring method are, of course, quite difficult and expensive to make.