284 Proceedings of the Royal Society of Edinburgh. [Sess. 
Cu 3 A1, (c) the 60 per cent, bronze consists of CuA1 2 and a eutectic alloy, 
(d) the 70 per cent, bronze is chiefly eutectic with the addition of a solid 
solution of copper in aluminium. Accordingly, the two aluminium alloys 
which show a specially marked improvement in magnetic quality when 
cooled to liquid air temperature are the two bronzes which contain free 
copper. The same two (viz., the 5 per cent, and 70 per cent, bronzes) also 
show an increased retentivity in the quenched state. This again agrees 
with the results obtained for metallic copper.* The 10 per cent, aluminium- 
bronze does not contain free copper, and does not improve on quenching. It 
shows, however, an increased retentivity at liquid air temperature. Accord- 
ingly, one or both of the compounds Cu 4 A1 + and Cu 3 A1 is magnetic. The 
60 per cent, aluminium-bronze, which consists of CuA1 9 and eutectic, is 
practically non-magnetic. Turning now to the 30 per cent, manganese-bronze, 
we have another alloy containing free copper. It exhibits the same peculiar 
properties as the two aluminium-bronzes which had free copper, in so far as 
its retentivity is greater at liquid air temperature than at 15° C., and is 
greater in the quenched than in the cast condition. The manganese which 
is a constituent of this bronze is, comparatively speaking, strongly magnetic,! 
but it will be seen that the effects of liquid air and quenching are the 
reverse of those found in the manganese-bronze. In a paper shortly 
to be laid before this Society by Mr J. G. Gray and one of us, it will 
be shown that manganese -steel does not give an increased residual 
magnetism after quenching, as does manganese-bronze, and further that 
when in the normal condition its quality degenerates slightly when the 
material is cooled to —190° C. Manganese-steel is therefore somewhat 
similar to pure manganese in its magnetic properties, and gives effects 
altogether unlike those found in the purest copper. Accordingly, as 
manganese-bronze resembles copper in its magnetic properties and is 
essentially different from manganese and manganese-steel, it seems natural 
* J. G. Gray and A. D. Ross, “ fiber die Herstellung permanenter Magnete aus Proben 
nahezu remen Kupfers,” Phys. ZeiL, x., No. 2, S. 59. 
t The existence of tlie compound Cu 4 A1 mentioned by Carpenter and Edwards in the 
report, loc. cit ., has been questioned by other experimenters. See in this connection the 
investigations of Gulliver, Proc. Inst. Mech. Png., 1907, p. 345 ; Curry, Journ. Phys. Chem ., 
1907, p. 425 ; Gwyer, Zeit. Anorg. Chem. , 57, S. 125, 1908 ; Guillet, Revue de metallurgie , 5, 
p. 413. The occurrence of Cu 3 A1 is generally accepted, and the existence or non-existence 
of a compound Cu 4 A1 does not materially affect the present discussion. 
| The manganese used in this test was a specially purified sample supplied by E. de Haen 
of Seelze. That its magnetism was not due to iron impurity was shown by chemical 
analysis. The amount of iron present was probably less than one part in 10,000, and 
certainly did not exceed one part in 5000. Taking the upper limit, it follows that the iron 
present was less than Aq of that which would be required to account for the residual 
magnetism. 
