108 
fracture, and furthur, as hydrochloric acid is much more 
volatile and of less specific gravity than sulphuric acid, it is 
only natural to expect that the effect of immersion in hydro • 
chloric acid will pass off more rapidly than of immersion in 
sulphuric. This experience fully confirms. 
Influence of Immersion in Acid on the Tensile Strain 
and Elongation. 
With a view of determining these interesting points a 
number of experiments were made in the following way, 
viz. : Small coils of iron wire were immersed in hydrochloric 
and sulphuric acids for different lengths of time, and then 
carefully tested for tensile strain in a very accurate machine, 
so constructed that the elongation of the wire while under 
strain could at any moment be ascertained. The weights 
could also be added quickly and without imparting any 
shock to the wires, points to which great importance should 
always be attached in experiments of this kind, as a slight 
shock or jar on the addition of a weight will often cause 
the rupture of a piece which otherwise would have stood a 
much higher strain. The length of the pieces tested was in 
all the experiments 10 inches between the dies of the 
machine, and their temperature at the time of experiment 
about 16° C. 
After the ultimate elongation and breaking weight had 
been ascertained with this machine, the coils were placed 
on warm plates or in hot chambers for some hours and sub- 
sequently tested in the same way. 
Experiments, the results of which are shown in tables 
A, B, C, were made in this way, and lead us to the follow- 
ing conclusions : 
1st. That immersion in hydrochloric acid for 1 hour 
diminishes the 
Tensile strain of annealed iron 29 Tibs, per sq. inch of section. 
5 , unannealed iron 2,3891bs. „ „ 
