I may here observe that I have been professionally engaged to inspect the effects, with a hope of finding the cause, of thirty-four cases of explosion, where the sacrifice of human life was above an average of two each, or nearly one hundred, and I never yet have found one single case which could not be clearly demonstrated to have been caused either solely by neglect of the superintendent, or from sheer ignorance on the part of the engineer constructing the arrangement of boilers. For every accident may _sweepingly be said_ to be occasioned by a want of space for the escape of the steam: a too small valve, in the first instance, and in the second, a villanous construction of what is called iron boiler plate--a concentration of the veriest rubbish, under the name of wrought iron, ever gathered together. For this reason, I have drawn the reader’s attention aside for a few moments. The improvement of boiler-iron may detain us slightly, if by the delay any good can be accomplished. For an inconsiderable increase of outlay, a boiler might be rendered doubly safe to what it is at present, by simply using moderate caution in the selection of scrap iron, a perfect cleansing of that scrap, and by fusing the bloom on the bed of an air furnace. The great advantage would be that you would get a stronger, a much denser, and consequently a much better, metal: nor is this all the advantage; you might use a very much thinner plate, which would yet be equally strong; and science will tell you that steam would be more easily generated, as heat is more rapidly conducted. There is a very handsome description of barrel-iron made, generally termed “Stub-Damascus.” The method of preparing it, is of late considerably altered. A quantity of old files are hardened, by being; heated red-hot and immersed in water, then broken in pieces with a hammer, and afterwards pounded in a mortar until the pieces do not exceed in size a corn of number five shot. A proportion of 15 lbs. of these to 25 lbs. of stubs, is fused together on the bed of an air-furnace, beaten down, and rolled into rods. The rod of 3-8ths of an inch square, is twisted like a rope, precisely in the same way as the Damascus. The effect of this winding, is to give a beautiful mottle to the barrel; which will be found depicted in plate No. 3. Another mixture, represented in plate No. 2, was first made by Mr. Wiswould, of Birmingham. It is a compound, so far as I have been able to ascertain, of three parts of steel to two of iron, intimately blended and intermixed, and twisted as just described. It is a most beautifully clean and dense iron; but the extreme twisting is to it, as to all, highly injurious and prejudicial. The twisting is similar to the Damascus; only that two twisted rods are welded together instead of three, and with the twist of the strands running in opposite angles, as depicted in the wood-cut below. [Illustration]