166 "Mr. Napier on Copper Shealhing, 



as on the vessel, and with this view he adds, " I have from twenty to 

 thirty samples, distinguished for good or bad sea wear, fixed to a buoy in 

 the tide-way under exactly similar conditions, and when these come to be 

 stripped oif, if the greater or less waste correspond to their previous sea 

 wear, it may be then fairly referred to quality of the metal, and will form 

 a more trustworthy ground for analytical inquiry." The results of these 

 trials with an analysis of each specimen, I hope, will yet be given to the world. 

 A trial somewhat similar was made at the request of Dr. Percy, by 

 Captain James. Specimens of different coppers were kept in sea water 

 for nine months, the loss of each per square inch is given thus : — 



Electrotype copper lost, 1 '4: 



Copper with arsenic, 1"2 



Copper with phosphorus, none. 



Specimen copper marked "fi-om Frolic," , 1*12 



Copper (suppose cementing), 0"8 



Copper from dock-yard, 1-66 



Do. do 3- 



Do. do 2-48 



Do. do 2-33 



Yellow metal (Muntz's), 0-95 



Here again want of careful analysis of every specimen, and particulars of 

 condition, render this otherwise interesting expei"iment useless as data 

 for a proper investigation ; however, the object of the experiment was no 

 doubt gained by the comparing of alloys of copper and phosphorus with 

 ordinary metals. The results are interesting, and may be usefully applied. 

 The analysis of such an alloy is given in the same paper, whether the 

 exact one subjected to the above experiment is not mentioned — 



Copper, 95-72 



Iron, 2-41 



Phosphorus, 2'41 



100-54 



Experiments from which we are to deduce an application to such pur- 

 poses as sheathing, may lead to false results, not being in accordance 

 with the conditions of application, such as where one sheet of copper 

 overlaps another, making a connection extending over the whole external 

 surface of a ship, and embracing thousands of plates. Where a slight 

 variation in the composition of a few will induce an electrical action 

 throughout the whole, and thus give results entirely diflerent to suspend- 

 ing any single sheet, so that we must make our experiments under the 

 same condition, or have a thorough understanding of how to apply the 

 results got from single sheets to the conditions to which these may be 

 applied, such as the clear conceptions which characterises Sir H. Davy's 

 inquiry, and from which I have no hesitation in saying, that were a ship 



