REPORTS 
ON 
THE STATE OF SCIENCE. 

Third Report upon the Action of Air and Water, whether fresh or 
salt, clear or foul, and of various Temperatures, upon Cast Iron, 
Wrought Iron, and Steel. By Ropert Mauer, Mem. Inst. C.E., 
M.R.I_A. 
283. Tue first Report upon these subjects which I had the honour of pre- 
senting contained a statement of the condition of our knowledge therein up 
to that time, and cleared the way by the removal of certain errors as to the 
supposed methods of protecting iron from corrosion: it also indicated the 
principal directions in which further information was requisite in six deside- 
rata which demanded experimental answers. 
The second Report supplies information as to three of these, and less com- 
pletely as to the remaining three; and as in course of inquiry some other 
correlative branches of investigation suggested themselves, so it also enters 
pretty fully into the question of the protection of iron from corrosion under 
various conditions by the application of zinc in different forms ; of the causes 
of variation of specific gravity, and its effects upon the corrodibility of cast 
iron; of the comparative durability and best constitution of paints or var- 
nishes for the preservation of exposed iron, upon which several experiments 
are given; and also gives the first set of tabulated results as to the corrosive 
action of air and water upon cast iron under the five several conditions of 
experiment. One of the most important objects of those tabulated results 
was to determine the actual loss of metal by corrosion in a given time and in 
given conditions of most of the principal makes of cast iron in Great Britain, 
and hence to find their relative durabilities when used in construction, and 
by subsequent discussion of the results obtained to discover, if possible, upon 
_ what durability depended, whether upon the nature of the constituents of the 
compound alloy known as cast iron, or upon their proportions, or upon either 
of these in connection with the state of aggregation of the mass. 
The first period of exposure of about eighty-two different sorts of iron 
(chiefly cast iron) occupied 387 days, and from this alone the above conclu- 
_ sions might have been sought; but it became obvious, in course of inquiry, 
that the original state of the metallic surface when first exposed had much to 
do with its rate of corrosion, and that this became subsequently modified as 
_ it proceeded, and thus that the amount of loss of metal by corrosion might 
not follow a law of equidifference, but might increase or decrease in rate upon 
continued exposure. To arrive, therefore, at greater certainty in assigning 
a the practical engineer the actual loss of metal after long periods of expo- 
843. , B 
