1825.] Sir H. Davy ou Copper Sheatlwig. 297 



III The proportions of sulphate of lime indicated (15) and 

 (15') in the aslies of the soil, are not so great as those uaich 

 really exist in it, because, during the calcmatiju, a portion ot 

 sulphuric acid is decomposed. ^ , , . 



IV. It is probable that a portion of phosphate of magnesia is 

 combined with phosphate of ammonia. 



Article VII. 



Additional Experi.nents and Observations on the Application of 

 Electrical Conibiuationa to the Preservation oj the i.opper 

 Sheathing of Ships, and to other Purposes. By Sir Humphry 

 Davy, Bart. Pres. RS.* 



I HAVE already had the honour of communicating to the 



Royal Society the results of my first researches on the modes of 



preventing the chemical action of fluid menstrua, such as sahne 



solutions, or sea water containing air, on copper, by the contact 



of more oxidable metals. 



For some months I have been engaged in a series ot nev^ 

 experiments on this subject, so important to the navigation and 

 commerce of the country : and through the liberal and enhg-ht- 

 ened views of Lord Melville, and the Lords of the Admimlty, 

 who desired the Commissioners of the Navy Board and of the 

 Dock Yards to give me every assistance in their power, and all 

 the facilities which our magnificent Naval establishments at 

 Chatham and Portsmouth furnish, 1 have been enabled to con- 

 duct mv operations upon a very large scale. At this advanced 

 i)eriod of the session, it will be impossible for me to give more 

 than a very short notice of experiments which have been tried 

 under a ^-"reat variety of circumstances, and the details of which 

 would occupy some hours in reading; but I cannot deprive 

 myself of the" pleasure of stating the satisfactory and conclusive 

 nature of the results, many of w^iich have even surpassed my 

 expectations. ^ r .i • 



Sheets of copper, defended by from Vv to -nnnr part of their 

 surface of zinc, malleable and cast iron, have been exposed, tor 

 many weeks, in the flow of the tide in Portsmouth Harbour, and 

 their wei<rhts ascertained before and after the experiment. 

 When the metallic protector was from ^^ to -^U, there was no 

 corrosion nor decay of the copper ; with smaller quantities, 

 such as from ^.-.r to -^U, the copper underwent a loss ot weight, 

 wliich was ^rreater in proportion as the protector was smaller ; 

 and as a proof of the universality of the principle, it was tound 



« From tbc PliiloKophicRl Transactions for 1821, Part II. 



