188 REPORT — 1860. 



It Mill be seen that a very considerable portion of the copper plate has 

 been dissipated, that the surface has been sweated down, and in some parts 

 the whole substance has evaporated away. Bright crystals of red oxide of 

 copper line the wasted surface, which is also covered above with a coat, 

 |-th of an inch thick, of mixed crystalline oxides of copper and lead ; and 

 in the hollow which the dissipation of the metal has left between it and the 

 indurated sand, is a sublimate consisting of fine twisted coherent threads of 

 metallic copper, like those met with in mines and slags. Where nearest to 

 the lead, it has so intermixed its exhalations with those proceeding from 

 that metal as to have spread over the upper leaden surface a coating of green 

 crystals, consisting of a double oxide of copper and lead. Beneath, and round 

 the lead, at its contact with the sand (which below has penetrated its sub- 

 stance without altering its form), runs a pink skin, marking the path of the 

 red oxide of copper. I cut the lump of lead in half, and found it not only 

 traversed in the middle by a seam of mixed oxide, but, what was still more 

 remarkable, dotted with spots of metallic copper, which had found their way 

 to the very centre of the mass, and even reached the opposite side. 



That it was the metal in this case, as in that of the zinc, which became 

 volatile, and was subsequently deposited in the form of specks and filaments 

 of copper in some places, and combining with oxygen, as a crystallized oxide 

 in others, cannot be doubted. To attribute these effects to thermal electricity 

 would not be consistent with the facts ; for there was here no contact, and no 

 circuit. The penetration of the lead by the molecules of copper may be 

 called Cementation, and be supposed to be due to capillary attraction of pores 

 distended by heat acting on the volatile particles. 



But the surprising part of the result is, that the sublimation of copper by 

 heat should have taken place at so Iowa temperature. These four metals, in 

 close proximity, and all acted upon in the same manner, were their own 

 mutual thermometers. It was impossible that the heat to which the copper 

 plate, as a whole, had been subject could have been higher than the melting- 

 point of the unfused lead and tin. I can attribute this unexpected fact to 

 no other cause than the continual and protracted passage of hot currents of 

 air and vapour, mingled perhaps with carbonaceous gas from the neigh- 

 bouring wooden boxes* ; and it seems probable that if the central portion 

 of the bottom stone had withstood to the end the action of the furnace, or 

 if the buried boxes had been protected with a vault of brick, more light 

 might have been thrown on the transfer of molecules at moderate tempera- 

 tures by similar effects produced on other materials. 



I owe an apology for having delayed this Report much longer than I 

 should have done, had the bulk of the experiments been attended with better 

 success. I have been reminded of them by the design of a member of the 

 Association to institute some of a similar character with the added conditions 

 of pressure and steam. Whoever should now undertake such experiments 

 would conduct them on the vantage ground of the later researches which I 

 have here noticed, and might obtain results of high interest to geological and 

 chemical science. It may be doubted whether heat protracted through many 

 years, or even extraordinary pressure, may be essential elements of such 

 results. The unintermitted presence of volatile materials, for a considerable 

 time, passing over and dwelling among those of greater fixity at temperatures 

 mounting up to a red heat, may be the only needful condition ; and if a fur- 



* If I am right in believing that an oolitic Echinus, Pecten, and Coral, and an Ammonite 

 from the Lias, which I recovered from the furnace, are those marked in the Plan with the 

 Nos. 8, 9, 10, then, as these were reduced to alkalinity, though without change of form or 

 markings, it would follow that the carbonic acid under the same circumstances separates 

 from lime at an equally low temperature of the mass, under the partial action of hot currents. 



