The reference thus made to the popular theory of some lost art of hardening the native copper, afforded an opportunity of testing it in reference to the Brockville relics. They were accordingly submitted to my colleague, Professor Henry Croft, of University College, Toronto, with the following results: The object of the experiments was to ascertain whether the metal of which the implements are made is identical with the native copper of the Lake Superior mines; or whether it has been subjected to some manufacturing process, or mixed with any other substance, by which its hardness might have been increased. A careful examination established the following conclusions:—No perceptible difference could be observed between the hardness of the implements and that of metallic copper from Lake Superior. The knife or small dagger was cleansed as far as possible from its green coating; and its specific gravity ascertained as 8·66. A fragment, broken off the end of the broad, flat implement, described as a “copper knife of full size,” having been freed from its coating, was found to have a specific gravity of 8·58. During the cleaning of this fragment, a few brilliant white specks became visible on its surface, which appeared, from their colour and lustre, to be silver. The structure of the metal was also highly laminated, as if the instrument had been brought to its present shape by hammering out a solid mass of copper, which had either split up, or had been originally formed of several pieces. These laminæ of course contained air, and the metal was covered with rust, hence the specific gravity. The process by which a flat piece of copper has been overlapped, and wrought with the hammer into a rude spear-head, is shown in the accompanying illustration. A portion of very solid copper, from Lake Superior, of about the same weight as the fragment, was weighed in water, and its gravity found to be 8·92. The specific gravity of absolutely pure copper varies from 8·78 to 8·96, according to the greater or less degree of aggregation it has received during its manufacture. The fragment was completely dissolved by nitric acid; and the solution, on being tested for silver by hydrochloric acid, gave a scarcely perceptible opacity, indicating the presence of an exceedingly minute trace of silver. The copper having been separated by hydro-sulphuric acid, the residual liquid was tested for other metals. A very minute trace of iron was detected. The native copper from Lake Superior was tested in the same manner, and was found to contain no trace of silver, but a minute trace of iron. From this, it appears that the implements are composed of copper almost pure, differing in no material respect from the native copper of Lake Superior. [Illustration: FIG. 68.—Brockville Copper Spear.]