Very slight bands may be forced on by levers: thus, wagon makers use a lever or jack, such as in [Fig. 1428], for forcing the tires on their wheels. The wheel is laid horizontally on a table as shown, and the tire a forced out by the vertical lever, the arm b affording a fulcrum for the lever, and itself resting against the hub c of the wheel.
The following extracts are from a paper read by Thomas Wrightson, before the Iron and Steel Institute of Great Britain.
“The large amount of attention bestowed upon the chemical properties of metals, and the scientific methods adopted for their investigation, have led to the most brilliant results in the history of iron and steel industries. It must not, however, be overlooked that iron and steel have highly important properties other than those which can be examined by chemical methods. The cause for so little having been done in accurate observation of the physical properties of iron is twofold: 1. The molecular changes of the metals are so slow, when at ordinary temperatures and when under ordinary conditions of strain, that reliable observations, necessarily extending over long periods, are difficult to obtain: 2. When the temperatures are high—at which times the greatest and most rapid molecular changes are occurring—the difficulties of observation are multiplied to such an extent that the results have not the scientific accuracy which characterizes the knowledge we have of the chemical properties of metals.
“The object of the present paper is to draw attention to some phenomena connected with the physical properties of iron and steel, and to record some experiments showing the behavior of these metals under certain conditions.
“In experimenting the author has endeavored to adopt methods which would, as far as possible, eliminate the two great difficulties mentioned.
“It is obvious that the possible conditions under which experiments may be made are so numerous that all which any one experimenter can do is to record faithfully and accurately his observations, carefully specifying the exact conditions of each observation, and this must eventually lead to a more complete knowledge of the physical properties of the metals.
“The author’s observations have been led in the following directions:—
“1. The changes in wrought and cast iron when subjected to repeated heatings and coolings.
“2. The effect upon bars and rings when different parts are cooled at different rates.
“3. These changes occurring in molten iron when passing from the solid to the liquid state, and vice versâ.