Mr. Napier on Copper Sheathing. 165 



the copper clean, they were positive. It is to be regretted that an 

 analysis of these nails experimented upon was not given, the omission of 

 which takes from the value of the experiment. I here give the analyses 

 of three qualities of sheathing nails, which may be taken as the general 

 character of the nails now in use for copper sheathing. The first two are 

 by Dr. Percy, taken from the Chemical Gazette for 1850: — 



No. 1. 



Copper, 52-73 



Zinc, 4118 



Lead, 4-72 



Tin, — 



98-63 



No. 2. 



Copper, 62-62 



Zinc, 24-64 



Lead, 869 



Tin, 264 



98-59 



No. 1 is said to have corroded rapidly, becoming rotten at the heads and 

 breaking off; No. 2 is good, and had been taken from a ship's bottom 

 after a voyage to India and back. 



The next. No. 3, are sample nails exhibited at the meeting of the 

 British Association, Swansea, analysed by Mr. John Cameron : — 



No. 3. 



Copper, 600 



Zinc, 34-8 



Lead, 0-7 



Tin, 3-8 



Iron, 0-3 



99-6 



The application of any of these nails to fasten copper is a very question- 

 able practice. 



About two years ago, Mr. Prideaux resumed the subject of inquiry 

 into the causes affecting copper sheathing, in a series of papers to the 

 Mining Journal, in which it appears that little or no advance has been 

 made to our knowledge of this subject since his former communication to 

 the British Association. In these letters he says, " With respect to the 

 quality of the metal, I have been called upon to analyse many specimens 

 of good and bad wearing sheathing, old and recent, and to examine a 

 great many more, and have not found in the analyses any characteristic 

 or constant difference between the bad and the good, nor have those which 

 wasted quickest, nor wore worst at sea, been uniformly or decidedly more 

 Busceptible to corrosive agency in the laboratory than the very best old 

 samples." 



How valuable would a table of these analyses have been, to enable 

 others to draw conclusions, as very often men employed constantly in any 

 particular branch investigate with certain preconceived expectations, 

 which cause them to overlook many important circumstances ; hence we 

 find Mr. Prideaux expecting the same kind of results in the laboratory 



