33.94 per cent of zinc have nearly the same figures for hardness, varying only from 427-08 to 472.92. This corresponds with what has been stated in regard to the similarity in strength, colour, and other properties of alloys between these compositions."

SHEET BRASS AND WIRE BRASS

§ 28. For rolling into sheets, and drawing into wire and tubes, it is in the highest degree essential that the metals employed in alloying should be pure and consist only of copper and zinc. One of the most injurious substances to brass is antimony, which is occasionally found in common copper. Brass laminates well in the rolling mill in the cold, as long as it is kept sufficiently soft by occasional annealing, which, on account of the expansion of the mass by heat, releases the strain put upon its particles by the pressure of the rolls. The malleability and ductility of brass depend upon the composition; and for alloys of a full-yellow colour, the most suitable proportions are found between 66 to 73 per cent of copper and 34 to 27 per cent of zinc. The following table gives the composition of a few English and foreign varieties:

For hot-rolling, the alloys known as Muntz' metal, or more commonly yellow metal, are employed. They vary in composition from 56 to 63 per cent of copper and 42 to 37 per cent of zinc.1 Mr. George Frederick Muntz of Birming

1 Percy's Metallurgy, p. 619.

ham took out his first patent for yellow metal as a sheathing for bottoms of ships and other vessels in 1832. The proportions specially recommended in the specification are 60 per cent of copper and 40 per cent of zinc; but these proportions may be varied from 56 up to 63 per cent of copper. Best selected copper and foreign zinc are directed to be used. The metal is cast into ingots, and rolled while hot into sheets, which, when finished, are pickled in dilute sulphuric acid to remove the adhering scale, and afterwards swilled in water. In the same year Mr. Muntz obtained a second patent for an improved manufacture of bolts, and other ship fastenings. Precisely the same proportions of copper and zinc are claimed as in the first patent. In 1846 a third patent was granted to Mr. Muntz for the use of an alloy consisting of 56 per cent of copper, 401 of zinc, and 33 of lead. In the specification it is directed that only the purest metals should be used, and that the alloy is to be cast into ingots, which are to be rolled at a red heat, and treated in other respects in the same manner as stated in the specification of the first patent. Dr. Percy states that he has succeeded in rolling brass well, which, on subsequent analysis, was found to contain not less than 8 per cent of lead.

The theory assigned by Mr. Muntz for the application of his alloy is, that by exposure to sea-water the zinc is slowly and uniformly corroded over the entire surface, whereby the attachment of barnacles, etc., is prevented. Yellow metal sheathing has entirely superseded copper sheathing in the merchant service. Its special advantages are stated to be, that it keeps the bottoms of ships cleaner, and costs considerably less than copper sheathing. An experienced yellow metal manufacturer states that the proportion of zinc in the alloy should not exceed 38 per cent; and that if it exceeds this proportion, the sheathing is apt to become friable; and that if it is sensibly below this proportion, it wears away too rapidly. In 1874 an alloy composed of 62 parts copper, 37 parts zinc, and 1 part tin, was proposed by Mr. Farquharson for naval brass. To insure the best results he recommends