XX Vill. ABSTRACT OF PROCEEDINGS. 
and tear of atmospheric and other influences. Any given 
structure, whether it be a ship, an engine, a house, or a 
bridge, will, if left to itself, become weathered, perish, and 
decay,unless protected. The many hosts to be thus reckoned 
with are:—Chemical and electrical influences, mechanical 
and meteoric changes, erosion by sand, wind, and rain, 
factory-chimney emanations, all more or less accelerated 
by contraction and expansion, together with biological 
influences and animal depredations. It is found that by 
examining the structure of a metal, much useful informa- 
tion may be obtained as to its powers of resistance under 
given circumstances. A section of a metal for instance ig 
highly polished and then etched by an acid, an alkali, or a 
peroxide, either applied directly or by electrolytic methods. . 
From the visible grain, texture, or structure, as seen under 
the microscope, good and bad materials may be differen- 
tiated one from another. This method of examination and 
testing materials has come rapidly into use during recent 
years, and is particularly useful in the case of iron, steel, 
bronze, brass, Muntz, and other yellow metals. The rust- 
ing of iron and steel is dealt with, the author referring to 
experiments made from time to time during the last fifteen 
years, and the immediate cause of the publication of this 
paper at the present time was owing to a paper published 
in a recent number of the Journal of the Chemical Society 
by Dunstan, followed by a similar one by Moody on the 
rusting of iron. The former observer lays stress on the 
action of hydrogen peroxide, while the latter accounts for 
rust by the action of carbonic acid, which action he com- 
pares to the action of any mineral acid on iron with the 
consequent liberation of hydrogen. Petit, in 1896, showed 
that the mere presence of carbonic acid gave rise to corro- 
sion and formation of ferrous carbonate, which is one of the 
antecedent products in the formation of rust. The author 
was engaged in a work of investigating the causes of the 
