RIEDERER-LITHOPONE. 403
nvnilablc for gnlvnnising, and could bo produced very cheaply.
Dr. G. T. MORGAN asltcd wlictlicr zinc dust vnporiscd more rendily thnn tho masrire metal, and wlicthcr at tho t~mpcrnturo of tlic proccss zinc dust liad nny npprecinbly different vnpour pressurc to zinc itself. Mr. COWPER-COLES, in reply, said tho first question raised \vns thnt of cost. Undoubtcrllg, the cost of vnpour gnlvnnising was lcss than thnt of hot gnlvnnising, the chief rcnsons being thnL no zinc-iron nlloy wns formed, and tho whole of the zinc dust wns eonsumcd, and thcre was no mnste. If the zinc dust deteriorated n t all, i t could nlnnys bo rcnovntcd by tlic addition of carbon. Tlic tcinpernture required for vnpour @vnnising \vns very low as conipnrcd with hot gnlvnnisin ; it never nced cxcccd 0000 F., and wns qnito worlrnbfc cvcn at 5000 F.
In tlic cnsc of hot gnlvnnising. a lnrgc mnss of nietnl h o d to be Itc t moltcn dog nnd night; the molten zinc \vim continunlfy working on tho iron tnnlta to form a zinciron alloy, which ivng only snlcnblc nt n considcriibly reduced cost. Anotlicr saving c l k c t d by vnpour gnlvnnisin was thnt tlic cleansing had not to be cnrricd out to tfio somp dcgrec 01 nicety as in tho ordinnry hot proccss or in rlcctro-zincing. The next question rnised wns that of the tcmpcrof thcnrticles trcntrd nnd ilicir clnsticity. Among tlio specimcns exliibitctl, would bc found files and wntcli springs coated by thc vnpour proccss, which liad not lost their tcnipcr in nny degrcc. Spccimcns of iron plutc which lind becn vaponr gnlvnnised nnd thcn rolled and rlmwn. wcrc nlso exhibited.
With rclercncc to tlic rnnsirnuiii nnioiint of zinc oridc which could bc prcscnt iii tho zinc nnd yct give sntisfnctorv results, Iic hntl not tlic figures wit11 him, but Iic lind carried out mpcrimcnts cxtc~lding over mnny months, using tho snmc zino dust and ndding oril n siifficicnt quantity cncli dny. to iunkc good t ~i c nctunPmetal~ic zinc vnporised. It wns found tlint tho zinc bccnmc more oxidised cnch dny. ns the drunis wcrc opened when tlic zinc dust \vns still hot. If hc remembered rightly they found tlicy could gCt good rcsults with only 40 pcr ccnt. of rnctollio zinc present, nltliougli it took fiorncwlint longer to obtain tho snine w i g h t of zinc per squnrc foot on the iron nrticlcs under treatincut.