5 and 6 which were taken at a depth of i in. below
the tread in strips 4 and 3 respectively. No. 5 is
the finer, showing that the metal received more
work at that point than it did deeper in on
strip No. 3. This D tire had the fmest grain
and the most uniform structure of the samples
examined. On the other hand, the photographs
corroborate the chemical analysis of low carbon
content, possibly down to 0.50 per cent., as indi-
cated by the proportion of ferrite (white) and
pearlite (black).
Next in order of fineness of grain comes the C, B
and A tires respectively. Here again the relative
amounts of ferrite and pearlite give an approximate
indication of the amount of contained carbon, from
which it would appear that the B and C tires would
not run over 0.60 to 0.65 per cent, while the A may
rise to 0.70 pe^^ cent.
The material of the B tire shows a practically
uniform texture of grain throughout its whole depth,



30



with no decarbonization at the tread due to heat
treatment, although this is undoubtedly due to the
tire having been turned before being examined.
In the C tire, which was new, it will be seen that
the outer layer of the material next to the tread, as
indicated by the photograph No. 7, was decarbonized
by the action of the heat treatment to which it was
subjected. The presence of ferrite is very marked
all the way across the tread, but below the surface,
as indicated by the photographs Nos. 8, 9 and 10,
which were taken at depths of J in., ^ in., and i in.
