classes of steam hammer constructed by Messrs. Thwaites and Carbutt of Bradford, fig. 47 being the form most appropriate for small hammers, and fig. 48 that most appropriate for large. Messrs. Thwaites and Carbutt have had much experience in the construction of steam hammers, and for some time have made nothing else; and they state that they find that the hammers wrought by hand are preferred and are gradually taking the place of those wrought by selfacting mechanism, being under such easy and ready control. They state that they have made eighteen hammers for Messrs. Brown and Co. of Sheffield, the largest of which, a 15-ton hammer, was made with wrought-iron standards, and that they have also made several hammers with wrought-iron standards, and believe that this method of construction will come into general use. In the manufacture of the Bessemer steel, hammers of 5, 8, and 12 tons are habitually required. When the standards are of cast iron, the box form is now preferred to the old T form, and immense strength is necessary to enable the hammer permanently to endure the heavy shocks to which it is exposed. Messrs. Thwaites and Carbutt do not recommend hammers of the form shown in fig. 47 for larger sizes than 12 cwt., and such hammers are very suitable for the work of the smith's shop. But above that weight they recommend hammers with double standards, of the form shown in fig. 48, as being firmer and stiffer, and better suited for heavy work.

These hammers are controlled in their movements by two handles, one of which opens or shuts the stop valve, while the other gives motion to the working valve by which the steam is let into and out of the cylinder. This last valve is a balanced piston, so

that it is quite easily moved, and the hammer is consequently under ready control.

In Fig. 49 is shown a design by Messrs. Thwaites and Carbutt for a very heavy steam hammer carried

between two inverted cylinders, and the pistons, which are fixed, stand on the tops of two strong pillars. In this example the hammer acts by gravity alone. But it would be easy by making the bodies of the pillars less in diameter than the cylinder to aid the

THWAITES AND CARBUTT'S DOUBLE CYLINDER STEAM HAMMER, (ANOTHER FORM).

descent by the force of the steam. Fig. 50 represents another variety of this species of hammer, but the cross head is formed of wrought-iron plates riveted together. It is doubtful how far riveted work would stand the constant jars to which such an instrument would necessarily be exposed. In Fig. 51 is shown another form of double-cylinder hammer by the same designers. Here the cylinders are not inverted and the descent of the hammer is assisted by the steam.