CHEMISTRY. 247 



adherent species of varnish, then placed in a dock to which the cupriferous 

 solution would be admitted; and then by a series of piles, the requisite thick- 

 ness of copper would be deposited in from eight to ten days. The advantages 

 promised are diminution of cost and perfection of result ; for, there being no 

 joints in the copper, destructive animals could not penetrate, neither would 

 there be such an accumulation of weeds on the bottom as now r takes place. 



OX THE QUALITY OF COPPER FOR THE SHEATHING OF SHIPS. 



From a series of articles published in England during the past year on the 

 above topic, by James Xapier, F.C.S., we derive the follow r mg memoranda. 



Shortly after sheathing by copper was introduced, it was found that it did 

 not wear equally that while some lasted many years, others only lasted a few 

 years ; but it seems a general opinion that the sheathing, since its first intro- 

 duction, has greatly deteriorated, and since these last thirty or forty years 

 the rapid wear or waste in sheathing has become the rule, and instances of 

 long wear exceptions a fact which is certainly a serious matter, both for our 

 merchants and our government. The quantity of copper required for covering 

 a ship's bottom of course varies greatly. A ship of 120 guns consumed 4,738 

 sheets, weighing 17 tons 19 cwt, which, taken at an average cost of 100 

 per ton, amounts to 1,795 for the metal alone. This is not a great amount, 

 considering the value of the vessel, and the object for which the sheathing is 

 applied ; but it becomes a vast amount if renewed every three years, instead 

 of every twenty years. This is what makes the question a vital one. 



Mr. Prideaux was of the opinion that the deterioration of the copper, 

 recently so much complained of, originated in certain modifications introduced 

 by the smelters of copper ore, or from the introduction of certain qualities of 

 ore from abroad, which had affected the general quality of the metal. 



Although there is no absolute proof on this point, yet it is probable that 

 the supposition of Mr. Prideaux was in part correct. 



Shortly after the South American ores were introduced came into use 

 Muntz's yellow metal, an alloy of two equivalents of copper and one of zinc. 

 The success of working this alloy depends much upon the purity of the cop- 

 per used ; hence, with an increased supply of impure ores came an increased 

 demand for good quality of copper to make this alloy, which copper was, con- 

 sequently, taken out of the copper market. This was obtained by the pro- 

 cess termed " selecting ;" and to show the bearing of these circumstances upon 

 the subject under consideration, I must briefly describe the process and prin- 

 ciple of smelting and selecting. The ore is first calcined by being placed on 

 the floor of a large high roofed reverberatory furnace, and kept at a dull red 

 heat for several hours, w 7 hich expels a great quantity of the sulphur, and 

 oxidates a portion of the iron. It is then fused in a separate furnace, the 

 silica and oxide of iron combining forms scorias, or slag ; the copper with iron 

 and sulphur combines, forming what I have described as regulus ; the slag 

 or scorias floats, and is skimmed off, the regulus is tapped into a deep pit of 

 water which granulates it. This granulated regulus is again subjected to 

 calcining and fusing, until the iron -is mostly all oxidized, when the copper 

 remains as a sub-sulphuret, with a little iron and a portion of the impure 



