271 



On the Preservation of Sheet. Iron from Rust. [July 



what varnish or composition wouUl best preserve the exterior surtace 

 of such vessels from the rapid corrosion to which iron is so pecu- 

 liarly subjec t in a hot chmate. A series of experiments was uncler- 

 ttikon Willi tiiis view by myself at the requisition of Government; 

 and it may perhaps be useful to record the principal results in a 

 journal of science. 



Two sets of six wrought- iron plates, each measuring; three feet by 

 two feet, were tixed to two ivon triangles, the plates being prevented 

 by studs from coming into contact with each other. The same 

 varnishes were applied to both sets, one being intended for entire 

 submersion under water, the other to be only half immerged, in 

 v;ider to feel the united inHnence of air and water. 



The followint^ were the coatings applied. 



1. Common coal tar, laid on hot, and the plate heated. 



2. Theetsee varnish of Ava, one coat. This took a very consi- 

 derable time (two months) to dry, kept fust in a cool-room, and 

 afterwards in a room heated by furnaces.'* 



3. Native Dhuna, a|>plied to the iron hot, in a thick uneven 

 coat. 



4. Best white-lead painl, lliree coats ; allowed to dry and harden 

 for nearly three months. 



5. Coach-makers' varnish, two coats; dried rapidly. 



6. Spirit varnish, several coats ; warmed. 



7. White wax, melted on the surface. 



8. White wash, of pure lime water. 



9. The surface of the iron plate cleaned and guarded with an 

 edging of zinc soldered on. 



10. The natural surface of the rolled iron sheets, covered with its 

 usual hardened grey oxide. 



Many of the foregoing were employed from curiosity only, espe- 

 cially No. 6, the spirit varnish, which had on many occasions proved 

 quite ineffectual in preserving the surface of polished iron and steel 

 from rust in the atmosphere of Calcutta. 



The two frames were suspended as above described, one under 

 water, the other half immersed, from one of the unused dredging 

 boats near the Chitpur lock gates of the Circular canal, where they 

 were left undisturbed for three months, during a period of the year, 



* Major BuRNEY states, that three or four days are sufficient for the 

 varnish to dry when laid on wood, (Journal, Vol. I. p. 172.). I had not a 

 dannp vault in which to expose the plate as recommended by that officer, 

 and that may partly account for the delay in drying; but all varnish and paint 

 takes longer to dry on metal than on woo(', from its non-absorbent nature. 



