This section is from the book "A Practical Treatise On The Joints Made And Used By Builders", by Wyvill J. Christy. Also available from Amazon: Practical treatise on the joints made and used by builders.
Small wrought iron columns cut from gas tubing are sometimes united to cast iron sole plates by running with molten iron in preference to lead. Iron cramps used for uniting blocks of masonry put in hot, and run and completely surrounded with asphalte, are apparently secure against oxidation. Cast iron is much safer than wrought, unless the latter is galvanised where there is danger of the enveloping coat being abraded. It must bo admitted, however, that on this point opposite views are entertained, owing to all iron, and especially cast iron, corroding by pitting, and thus becoming perhaps honeycombed : or eaten into holes in the interior, whilst its visible surface or skin is barely affected. Sulphur is not much in vogue in : this country for running joints, its great advantage being that it expands in cooling. When it is employed, only just sufficient heat must be applied to melt it, otherwise it will run with difficulty, and it must not be allowed to burn. The surplus should be removed before it gets cold enough to become brittle, and sometimes dry sand is mixed with the sulphur with the object of hardening it. Ironwork is not dangerous when let into brickwork, but it is so in masonry without a protective coating, which in cast iron perhaps more or less effectively exists in its own skin.
This is so called on account of its enveloping the parts joined with an air-tight mass of rust, which becomes sounder by age. It is made by caulking the flanges of ironwork and the sockets of iron pipes previously partially packed with two or three rings of spun yarn, with a composition called iron cement, or rust cement, consisting of iron filings, borings, or turnings, and sal ammoniac mixed together in different proportions with or without sulphur. A good variety is described under Iron Cement Joint. The proportions of the components, however, vary in different receipts, one recommending sulphur, sal ammoniac (muriate of ammonia), and iron borings, in the respective proportions of 2, 1, and 80. These are to be separately powdered, and then well mixed together with water sufficient to moisten them into a paste, which will oxidise and swell and set on exposure to the air. It requires careful preparing and caulking also, otherwise the socket will be in jeopardy of bursting. The joint between hoop iron and mortar or cement is greatly strengthened by slightly rusting the iron.
This is similar to the corresponding joint of the Zinc Worker.
Besides the joint of the same name described in Section XI., and which is applicable to this trade also, there is another important connection occurring between the chains of suspension bridges and the saddles on which they ride that from analogy rightly goes by this term. The saddles on the piers carrying the chains of the Clifton Suspension Bridge are of wrought iron, placed on roller frames of cast iron, the rollers being of cast steel. In piping a similarly-named joint results from saddling a main with an iron band composed of two or more sections which are bolted together and caulked. The main is then retapped and the service thus becomes saddle-jointed.