Varnishes for Iron.

Manufacturer and Builder 5, 1869

The London Chemical News, which is reprinted in this city by Messrs. Townsend & Adams, gives a valuable report by Dr. Lunge on "The Preparation of Varnishes for Iron as Secondary Products in the Distillation of Coal-Tar," which we copy, as it must prove interesting and valuable to many of our readers:

"Varnishes f this description are very easily prepared by melting pitch with different matters obtained in the distillation. No substances other than those obtained in the distillation of tar are required, and all that is necessary in the manufacture is an iron vessel in a covered building. The form of vessel most convenient is a vertical cylinder, slightly concave at the bottom. About as much pitch as would be contained in a three-quart vessel is thrown in at a time, and a small quantity of oil added to facilitate the fusion of the pitch and to prevent its solidifying on cooling. Considerable heat i s then applied, and small quantities of oil added from time to time; before adding the whole of the oil, it is important that the melted mass should be allowed to cool so that the oil will not enter into ebullition. exact proportions can be of no service, as different degrees of consistence are required for different purposes. Samples are withdrawn from time to time, and allowed to become quite cold, to judge of the consistence of the material. The oil employed is the heavy oil of tar; and for ordinary kinds of paint for metal, pitch is melted with it as previously described. But for many purposes a simpler process still may be employed, especially in the manufacture of large quantities. Tar is placed in small retorts, the ordinary retorts are too large for the purpose,) and heated until the heavy oil commences t odistill over; then the fire is diminished, and the retort allowed to cool somewhat: the retort is then opened, a certain quantity of heavy oil added, and the mixture well stirred; all that remains to be done is to pour the mixture out, and the operation is finished. Varnish made in this way is preferable to tar, and dries sooner; according to the state of t he atmosphere, it dries in twenty-four or forty eight hours. By incorporating naphtha of the lowest quality - to do which the mass must still be warm - with the material made with light oil instead of heavy oil, a varnish may be obtained which will dry in an hour or less."