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Professor R. H. Thurston, who conducted the investigations for the United States Board, makes the following remarks on the preceding table :

"Alloys having the name of Bolley appended give compositions and commercial names, and mention valuable properties, such as are given in the column of remarks, but do not give results in figures as recorded by other authorities. The same properties and the same name are accorded by Bolley to alloys of different compositions, such as those which in the column of remarks are said to be suitable for forging. It might be supposed that such properties belonged to those mixtures, and not to other mixtures of similar composition. It seems probable, however, that when two alloys of different mixtures of copper and zinc are found to have the same strength, colour, fracture, and malleability, it will also be found that all alloys between these compositions will possess the same proportions, and hence, that instead of the particular alloys mentioned only being suitable for forging, all the alloys between the extreme compositions mentioned also possess that property.

"In the figures given from Mallet under the heads of order of ductility, order of malleability, hardness, and order of fusibility, the maximum of each of these properties is represented by 1.

"The figures given by Mallet for tenacity are confirmed by experiments of the author, with a few very marked exceptions. These exceptions are chiefly the figures for copper, for zinc, and for CuZn, (32.85 copper, 67·15 of zinc). The figures for CuZn, as given by Mallet, can, in the opinion of the author, only be explained on the supposition that the alloy tested was not CuZn2, but another containing a per cent of copper, probably as high as 55. The figure for the specific gravity (8.283) given by Mallet indicates this to be the case, as does the colour. The figure for ductility would indicate even a higher per cent of copper. The name watchmaker's brass in the column of remarks:

must be an error, as that alloy is brittle, silver-white, and extremely weak.

"The figures of Calvert and Johnson and Riche, as well as those of the author, give a more regular curve than can be constructed from the figures of Mallet.

"The specific gravities in Riche's experiments were obtained both from the ingot and from powder. In some cases one, and in some cases the other, gave highest results. In the table under the head of specific gravity Riche's highest average figures are given, whether these are from the ingot or from the fine powder, as probably the most nearly correct. The figures by the other method, in each case, are given in the column of remarks. The figures of Riche and Calvert and Johnson are scarcely sufficient in number to show definitely the law regulating specific gravity to composition, and the curves from their figures vary considerably. The figures of the author being much more numerous than those of earlier experimenters, a much more regular curve is obtained, especially in that part of the series which includes the yellow or useful metals. The irregularity in that part of the curve which includes the bluish-gray metals is, no doubt, due to blowholes, as the specific gravities were in all cases determined from pieces of considerable size. If they were determined from powder, it is probable that a more regular set of observations could be obtained, and that these would show a higher figure than 7·143, obtained from cast-zinc. Matthiessen's figure for pure zinc (7.148) agrees very closely with that obtained by the author for the cast-zinc, which contained about 1 per cent of lead.

"The figures for hardness given by Calvert and Johnson were obtained by means of an indenting tool. The figures are on a scale in which the figure for cast-iron is taken as 1000. The alloys opposite which the word 'broke' appears were much harder than cast-iron; and the indenting tool broke them instead of making an indentation. The figures of alloys containing 17.05, 20:44, 25·52, and

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."

§ 26. TABLE OF VARIOUS COPPER-ZINC ALLOYS

NAME.

Authority. Copper. Zinc. Tin. Lead. Iron.

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Name.

§ 27. SOME VARIETIES OF MODERN BRASS

Jeweller's gilding Red

alloy

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Pinchbeck

Reddish-yellow 88.8 11.2

Oreide (French gold) Reddish-yellow

Talmi gold

Tissier's metal with

Red

Gold

Red

93.6

6'4

90

10

90.70 8.33

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