104 
and diminishes the 
Ultimate elongation of annealed iron 0’8 per cent. 
„ unannealed iron 0*83 „ 
2nd. That immersion in hydrochloric acid for 6 hours 
diminishes the 
Tensile strain of annealed mild steel 2,5631bs. per scp in. of section, 
and increases the 
Ultimate elongation of annealed mild steel 4 '7 per cent. 
When first I discovered that a decrease of ultimate elon- 
gation under strain was the result of immersion of steel in 
acid, I thought there must he some experimental error, and 
accordingly carefully selected 8 coils, all of uniform temper, 
and made 3 tests from each coil, the results of which are 
given in detail in table C. The singular regularity of these 
tests must be said to remove all doubt as to the truth of 
the results of the first experiment. 
It then occurred to me that possibly lyrolonged immer- 
sion in acid might so decrease the breaking strain that the 
wire would not recover its original strength. For this pur- 
pose I carefully tested the elongation and breaking strain of 
the wire before immersion in acid and again after heating for 
5 days on a hot plate. The results of these experiments as 
given in tables D and E confirm this view, showing that 
there is 
1st. A permanent decrease in breaking strain after pro- 
longed immersion in 
Sulphuric acid of 12,2051bs. per sq, inch of section. 
, Hydrochloric „ 31,2751bs. „ „ 
Both these results are doubtless too high as the surface of 
the wire was pitted by the acid, consequently its actual sec- 
tional area was less than that calculated from the diameter 
as measured. 
2nd. A permanent increase in the elongation after pro- 
longed immersion in 
Sulphuric acid of 1 ‘7 per cent. 
Hydrochloric ,,2*17 „ 
Having examined the effect of acid on annealed steel it 
was next thought advisable to try the effect on unannealed. 
This was done with results as in table F, showing that the 
