MECHANICS AND USEFUL ARTS. 65 



metal, lead with tin, not, however, in the form of an alloy or mixture, but 

 so that each metal will be kept perfectly distinct, the tin or superior metal 

 being only exposed, while the lead or inferior metal is encased within. In 

 order to make such sheets or foils, a peculiar ingot or slab must be first 

 made, by which the whole amount of metals to be contained in the in- 

 tended sheet or foil must be joined at their surfaces, and retained in such 

 position that the subsequent action of the rolls shall not be able to dis- 

 place or extend one metal more rapidly than the other, for it is evident 

 that the lead, by reason of its being the softer and more yielding metal, 

 would be squeezed out in an undue proportion to the tin, were it not con- 

 fined on all sides by the tin. I therefore make the ingot or slab for roll- 

 ing, in the following manner : First, a metallic mould is made, which 

 shall determine the size of the slab to be cast ; the cavity in such mould may 

 be, say six inches wide, one inch thick, and ten inches long ; then prepare 

 a slab of lead, as much less in size than the cavity in the mould, as is de- 

 signed for the different proportions of the metals, say of the following 

 dimensions : five and one-half inches wide, nine and one-half inches 

 long, and half of one inch thick. This, when suspended in the centre of 

 the mould, will leave a clear space all round, and the tin can then be poured 

 in. To accomplish this suspension properly, I prepare small blocks or 

 posts of tin, of a length equal to the space left between the lead and the 

 sides of the mould, and by placing these around on all sides, I sustain the 

 slab of lead exactly in the centre. The surface of the lead being properly 

 clean, or properly fluxed or coated with an alloy of lead and tin, the mould 

 is ready to receive the tin which is poured in, until the whole of the space 

 is filled, the lead being then completely encased within it. The posts of tin 

 of course combine with the fluid tin poured in, and form part of the solid 

 mass. The slab is now ready for the rolls, and may be extended into 

 sheets and foils of any degree of thinness. From this construction of the 

 slab or ingot, it is evident that the lead cannot escape from the tin, but 

 must extend and be pressed out with it, in exactly the same manner, and 

 at the same rate, thus insuring perfect equality in regard to the given pro- 

 portions first adopted, as to every part of the sheets, no one part having 

 more lead in combination with it than another. Thus, foils or sheets are 

 produced, which, for many of the purposes to which those of pure tin are 

 applied, such as for wrappers of tobacco, caps for bottles, &c., are fully 

 equal in the qualities required to those of pure tin, while they are fur- 

 nished at a greatly reduced cost. Scientific American. 



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TEMPERING AND GRINDING STEEL. 



Mr. Chesterman, of Sheffield, England, has lately invented and patented 

 several vaiuatle improvements in hardening and tempering steel, and in 

 grinding, glazing, buifing, and brushing steel and other metallic articles. 

 The process of hardening and tempering apply principally to thin steel, 

 such as is used for saw-blades, for example, The hardening is effected in 



