Page:Report from the Select Committee on Steam Carriages.pdf/91



John Farey, Esq. 10 August, 1831. have had many trials of it; and I am well acquainted with Mr. Gurneys; the former uses flat chambers of thin iron plate standing edgways upwards over the fire in parallel vertical planes; the latter uses small tubes (such as gun barrels are made of,) to contain the water, the fire being applied on the outsides of the tubes. In Mr. Gurney's boiler I think the subdivision of the water into small spaces is carried too far, because the steam cannot get freely away out of such small tubes as he uses (and they are also of great length) without displacing much of water which ought always to be contained within them. By an ingenious arrangement of connecting pipes and vessels which he called Separators, be collects all the water which is so displaced along with the steam, and returns it again into the lower ends of the same tubes, and thus avoids the evil of water boiling over into the engines; but that makes only a partial remedy for the diminished production of steam, which is attendant on the absence of the water from the heated tubes, and the still greater mischief of burning and destroying the metal. Hence the evil of burning out the tubes is very great. Also his separators hold a considerable weight of water, from which no steam is generated; and they require to be heavy in metal, to render them quite safe and strong. Mr. Hancock has taken the middle course in subdividing the water in his boiler, having all that can be required for safety, and the weight I believe, on the whole, to be less than that which will produce the same power of steam; for, owing to the freedom with which the steam can get away in bubbles from the water without carrying water with it, the surface of the heated metal is never left without water. Hence a greater effect of boiling is attained from a given surface of metal and body of contained water, and that with a much greater durability of the metal plates, than I think will ever be obtained with small tubes.

Do you think there is a danger of such an explosion as could do injury from the mode in which Mr. Hancock's boilers are constructed?—That danger I hold to be very slight; the metal of Mr. Hancock's