MESSRS. EDITORS—You inquire, in a late number of the " Scientific American," " what was the cause of the bursting of the blast pipe of the Crane Iron Works, Pa. V I will endeavor to answer. I am not aware of the circumstances of the explosion, but I believe you will find the cause as I shall describe it. If I am correct, the explosion was not caused by the blast, nor while the blast was in operation, but in putting#n the blast, just as a boiler explodes when putting on the pumps. The cause of the explosion was gas from the furnace, the pipe having become filled with it while the blast was gff. When the blast is put on, the gas is forced back into the furnace or rather explodes on the first turn of the cur-rent to the furnace instead of from it, as it was before the blast was applied. You will observe that the draught, as I have stated, is, in the first place, from the furnace, sometimes caused bv the wind blowing down the chimney ; sometimes I have noticed quite a strong natural draught into the pipe. The tuyeres are placed low, near the bottom ot the furnace, a reason why the gases have not been more consumed when entering the pipe. Furnaces ought all to have an opening of about two or three inches in diameter, and at the end of the bend, where the pipes ascend or descend from the tuyeres, with a slide or cover, which should always be open when the blast is not on the furnace, this causes a draft into the furnace, arid prevents any from it. As we are on explosions, I ask the scientific world,—" did you ever see our foundry-men pouring melted iron into a pailful of water to warm it in winter, often causing a steam explosion on a small scale ; here is a pail of water without any power, into which you can pour melted iron to a certain extent in perfect safety, but the instant this is exceeded the pail is dashed into a hundred pieces without any warning whatever; where is the utility of safety valves, false alarms, c, for this kind of explosion, when the top of an open pail won't do? pour yaaf water from engine pumps on red-hot inland the same result ensues. I have often ssfen roes ai e mom or less in this way ; a little experience, however, soon teaches a man how far to go with safety. Troy,N. Y., 1853. J. T. [The following is. another letter on the same subject:— " The blast-pipe which exploded, as mentioned in the " Scientific American," must have been charged {by stopping the blast) with di-carburet of hydrogen, formed by the distillation of coal in the furnace. It being nearly one half as light as air, would find its way into the pipe, and as it (C.HS) requires only about two volumes of oxygen, or a little more to render it highly explosive, when they started the blast it passed off like thnhcler. Salem, Mass., April, 1853. E. L. N."