656 
This standard of purity has only been gradually | 
attained, and we may hope for further improvement. 
The purity is a matter of importance, as it affects the 
value of the metal as an electrical conductor in two ways, 
for impurities not only lower the conductivity, but also 
increase the liability to atmospheric corrosion. The 
evidence as to the power of aluminium to withstand 
atmospheric influences, especially in towns or places 
where the air is bad, is somewhat conflicting, but on the 
whole it seems that the metal is fairly satisfactory in this 
respect. The thin film of oxide which immediately 
forms on the surface of the metal in air acts as a pro- 
tective coating. Mr. Morrison quotes an interesting illus- 
NARORE 
[OcTOBER 30, 1902 
per ton, of aluminium is found greatly to improve the 
finished casting ; the aluminium, by combining with the 
occluded gases, reduces the blowholes and renders the 
metal being cast more fluid and ultimately more homo- 
geneous. Though the actual quantity used in this way is 
but a small percentage of the metal to which it is added, 
the total consumption of aluminium for this purpose is 
very large. A second use for aluminium depending on 
the same principle has been devised by Dr. Goldschmidt 
for producing high temperatures, and has been applied 
to the welding of iron rails, pipes and so forth. A 
mixture of iron oxide and finely divided aluminium is 
used, and is ignited by means of a magnesium ribbon ; a 
very high temperature is immediately 
reached by the oxidation of the aluminium 
at the expense of the oxygen of the iron 
oxide. This process, having been only 
lately introduced, has not yet become of 
much commercial importance, but is full 
of promise. 
The extremely low specific gravity 
(2°6) of aluminium has naturally resulted 
in its use in cases in which weight is a 
drawback. Thus in naval and military 
equipments, in motor-car construction 
and like applications, the metal already 
finds considerable and increasing em- 
ployment. For cooking utensils the use 
of aluminium is steadily increasing ; the 
metal is eminently suited for this pur- 
pose, as, apart from its lightness, it is a 
good conductor of heat, is not liable to 
deteriorate in use and gives rise, if dis- 
solved, to perfectly harmless compounds. 
Applications of this kind may seem small 
individually, but in the aggregate they 
constitute no mean field for the metal 
to capture. 
The chief drawback to aluminium is 
its low tensile strength, which, for the 
cast metal, is only from five to eight 
tons per square inch ; but for this weak- 
ness its utility would be enormously in- 
creased. A certain amount of improve- 
ment can be effected by alloying a 
small quantity, generally less than Io 
per cent., of some other metal, such as 
nickel or copper, with the aluminium. 
The specific gravity of these alloys is 
only slightly higher than that of the 
metal itself, but the tensile strength 
may be made two or three times as 
great. Exceedingly valuable data relat- 
ing to a number of these light alloys are 
contained in the paper by Prof. Wilson 
to which reference has been made above. 
It is impossible to enter at all fully into 
the results obtained by Prof. Wilson, as 
the paper is itself so condensed as to 
Fic. 1.—The British Aluminium Company's Power-house at Foyers. 
tration of the tenacity. of this oxide film ; if the metal is 
cast into a mould and allowed to overflow, the film of 
oxide adhering to the molten metal that has run over 
acts as a syphon tube, and will syphon out a considerable 
quantity of the aluminium. 
The two most marked characteristics of aluminium, on 
which its principal applications depend, are its high 
affinity for oxygen and its low specific gravity. The 
former of these properties causes aluminium to play a 
part of considerable importance in the metallurgy of 
other metals. Thus im the casting of steel, iron, brass, 
&c., the addition of a small quantity, two to five pounds 
NO. 1722, VOL. 66] 
be little more than a summary, but a few 
of the more interesting conclusions may 
be briefly tabulated. In the accompany- 
ing table is shown approximately the effect of alloying 
different metals on the conductivity, specific gravity and 
strength of aluminium. 
Aluminium is now finding considerable employment as 
a substitute for copper as an electrical conductor, especi- 
ally in America, where it is used to a large extent in 
connection with the transmission of power over long 
distances. One of the most important of these installa- 
tions is the transmission of 12,000 h.p. from the Sno- 
qualmie Falls to Seattle and Tacoma, a distance of more 
than forty miles. In this scheme an alloy of aluminium 
with 14 per cent. of copper has. been used, the lightness 
