378 
TATURE 
[Fepruary 18, 1897 
question, the author says, ‘‘ has been definitely answered in the 
affirmative.” 
In dealing with the copper zinc alloys, the author reminds us 
that it is seldom an alloy solidifies sharply or at one tempera- 
ture, as water does. There are generally at least two freezing 
points; and in the industrial brasses, which never contain more 
than 45 per cent. of zinc, only three of the freezing points were 
referred to at first, although the scientific interest of the rest was 
considered later on. The chief point of interest in the paper 
was the consideration of the eutectic alloys. Of the several 
breaks in the curves of cooling points of most alloys, the first 
usually represents the falling out of a more or less pure metal, or 
some compound of the metal, from the cooling alloy. A second 
and sometimes a third break indicates the solidification of a 
eutectic alloy, that is a fusible metallic or ‘‘ mother liquor,” 
which solidifies at a definite temperature. In the copper zinc 
series there are several of these eutectic alloys. 
Guthrie introduced the designation ‘‘eutectic” alloy to 
denote the most fusible alloy of two or more metals, comparing 
it to the mother liquor of a salt solution, which remains fluid 
after the bulk of the salt hascrystallised out. The recording pyro- 
meter shows that as regards alloys the case is really far more 
complicated. Many alloys consist, when fluid, of more than one 
solution ; and each of the several solutions leaves, on cooling, a 
solid deposit and a fluid mother liquor. These mother liquors, 
however, do not usually unite with one another; and a com- 
plicated set of conditions is established, when the temperature 
has fallen sufficiently low for the whole mass to become solid. 
Each of these metallic mother liquors is a eutectic alloy. Some 
alloys—the lead-tin for instance—are of a simple character, and 
when fluid have only one eutectic alloy, that is, the deposits fall 
out from a single mother liquor. All the alloys which are used 
for the sake of their strength appear to be highly complicated. 
Thus in the alloys of copper and zinc there are at least four 
eutectic alloys, and in the copper-tin series there are at 
least six. 
The composition of eutectic alloys does not in general corre- 
spond to simple atomic proportions of the component metals, 
and the author considers there are theoretical reasons for sup- 
posing that a eutectic alloy cannot possibly be a chemical com- 
pound, It should be noted that in the cooling curves of some 
alloys, solidification, as shown, takes place over a somewhat long 
range of temperature. The point at which one constituent 
begins to crystallise has been called the higher freezing point, 
and the temperature at which the eutectic alloy solidifies out is 
called the lower freezing point. These two points are indicated 
by separate evolutions of heat. That the lead-tin series has 
more than one freezing point, is illustrated in a familiar way 
which has considerable industrial importance. A plumber 
making a ‘‘ wiped joint” uses a solder containing 66 per cent. 
of lead, and its pasty condition is due to the fact that it has two 
widely separated points of solidification, the alloy consisting of 
granules of solid lead in a fluid mother liquor. 
The facts above given lead up to a consideration of the 
mechanical properties of brasses, and the relation of these 
properties to the freezing point curve. In dealing with this 
part of the subject, the author had recourse to a series of 
diagrams exhibited on the walls of the theatre. Without the 
aid of these it will be impossible for us to treat the matter at 
all completely, even from the point of view of a brief abstract. 
Indeed the report—which is of great length—is so full of 
matter that we cannot hope to do more than give a few of the 
most prominent facts, which may serve to afford our readers an 
idea of its scope. Those interested in metallurgical research 
will naturally go to the original for fuller information. The 
method of investigation pursued was to heat an alloy in a steel 
cylinder and squeeze out the eutectic by hydraulic pressure ; the 
temperatures being noted, until finally a comparatively infusible 
residue is left. The several portions were then analysed, and 
the results of the analyses were given in an appendix. The 
results were discussed by the author in detail ; the dominant fact 
disclosed being that the maximum strength in the series of cast 
brasses occurs in the alloy containing 60 per cent. of copper. 
This alloy has practically only one freezing point. Further 
additions of zinc cause a rapid diminution of tensile strength and 
extensibility. The explanation given was that in these alloys 
the compound CuZn is unaccompanied by free copper. . In a 
series the summit of the curve representing extensibility coincides 
with the first appearance of the upper eutectic which falls out 
from the alloy that contains 71 per cent. of copper. This 
NO, 1425, VOL. 55] 
eutectic probably consists of a mixture of copper with the com- 
pound CuZn. The mixture of these soft and hard substances 
produces great strength, as is evident from the fact that the 
strongest alloy of the series consists almost entirely of this 
eutectic ; but the presence of the eutectic naturally diminishes 
the extensibility of a mass which contains more than a small 
amount of it. 
The addition of small amounts of iron to certain alloys of 
copper and zinc (Sterro and Aich’s metal) is next discussed by 
the author. The reason of the remarkable increase of strength 
thus produced has hitherto been obscure, but the facts are dis- 
closed by a comparison of the cooling curves given in the report. 
The alloy selected contained 61 per cent. of copper and 39 per 
cent. of zinc; and in the absence of iron there was a low 
eutectic point in the cooling curve at about 450° C. or 842° F., 
evidently due to the presence of a eutectic, which constituted a 
source of weakness. The added iron, however, entered into 
combination with the eutectic, forming with it a less fusible 
compound; for a cooling curve then showed that the low 
eutectic point was absent, and that the source of weakness had 
been removed. Moreover, the main solidifying point of the Aich’s 
metal was higher than that of the brass: which in itself is an 
indication of augmentation of strength. The facts thus established 
are probably of wide importance in metallurgical practice ; and 
where strength is desired, it would appear to be advisable, 
whenever a cooling curve reveals the presence of a low eutectic 
in an alloy, to add some third metal which will diminish the 
fusibility of the eutectic. Aich’s metal, when compared with 
brass of the same composition but without the 14 per cent. of 
iron, is greatly superior in strength. If it owes this superiority 
to the fact that a eutectic alloy does not remain fluid as the 
mass cools, it might be anticipated that the relatively high 
tenacity of Aich’s metal would be maintained at temperatures at 
which the brass would become weak. 
We have not space to follow the author further in his valuable 
and interesting research. He shows how the action of impurities 
is made clearly evident in connection with eutectic points, and 
has some most instructive remarks on the diffusion of metals, 
the latter a most important section of the report. Healso gives 
an account of improvements in the recording pyrometer by 
which great delicacy in recording is secured. The report con- 
cludes with a comparison of the thermo-junction with the air 
thermometer. k 
A good discussion, opened by Sir William Anderson and Sir 
William White, followed the reading of the report; but we 
have preferred to devote the space at our disposal to the report 
itself, as containing the most important matter. It may be said, 
however, that the tone of the discussion was entirely favourable 
to the report, its practical importance and value being dwelt 
upon both by the engineers and metallurgists present. 
DR. VERSIN, AND PLAGUE VIRUS. 
N view of the importance which attaches to Dr. Yersin’s 
discovery of the plague virus and its anti-toxin, the follow- 
ing notes on his work may be of interest. 
When a youth of twenty, Yersin had the rare good fortune 
to obtain an entrance to the Institut Pasteur. The extraordinary 
ardour with which he devoted himself to his work, rapidly won 
for him the admiration and respect of all his colleagues. When 
little more than a student, Roux signalled him out to assist him 
in those important researches on the toxin of diphtheria which 
have since become so memorable, and which were communicated 
to the scientific world under the joint names of the master and 
his pupil. f 
While at Tonkin, in the spring ot 1894, he received the 
request from the French Government to proceed to Hong Kong 
to study the plague which had recently broken out there. 
Yersin started off on his mission, and arrived in Hong Kong a 
few weeks after the plague had commenced its terrible career in 
that city—a career which had already claimed the lives of 300 
Chinese, and which was yet to exact a tribute of over 100,000. 
Yersin describes how, on reaching Hong Kong, he found the 
authorities busy rapidly erecting temporary hospitals, the exist- 
ing accommodation being quite inadequate to cope with the 
widespread dimensions of the epidemic. He obtained permis- 
sion to erect a small hut within the precincts of the principal 
hospital ; and there, in a concentrated plague atmosphere, he 
