sir. Napier on Evaporation of Water in Copper and Iron Vesseb. 291 



" Those io the * Thistle ' were made particularly strong ; and we think 

 it must give you gratification as the builder of the vessel, to learn it 

 is to that circumstance (the strength of her bulkheads) that the safety 

 of the vessel and the passengers on board of her is to be attributed. 



" Captain Dalzell, agent of the Glasgow underwriters, happened to be 

 on board the time of the accident, he was the only passenger who 

 ventui-ed to return with her, and he tells us that but for her strong 

 substantial bulkheads, the vessel must have gone down, and been 

 another case similar to the ' Orion.' The case altogether deserves the 

 notice of both shipowners and shipbuilders. 



" Yoiu's truly, 

 (Signed) " Thos. Cameron & Co." 



XXXVIII. — Experiments on the Evaporation of Water in Copper, Iron, 

 and Lead Vessels. By Mr. J. R. Napier. 



In many works on the steam engine it is stated that copper, on 

 account of being a better conductor of heat than iron, is therefore a 

 better material for steam boilers. 



In the last edition of the " Encyclopfedia Brittanica,'' for example, 

 Mr. John Scott Eussell affirms that " Copper is the best of all sub- 

 stances for steam engine boilers in a mechanical point of view ; that it 

 is not the best in a mercantile point of view," he says, "is proved by 

 the almost universal use of wrought iron boilers. Yet it is difficult to 

 sec why this should be the case, when we remember that copper lasts 

 for ever, is worth when old nearly two-thirds of its first cost, besides 

 being a much letter conductor of heat, and so saving /weZ and space. The 

 efficiency of a copper boiler," he adds, " in generating steam is to that 

 of iron as three to two." 



Mr. Damens, in his paper on Boilers in the Appendix to Tredgold on 

 the Steam Engine, states, " I confidently express my opinion that copper 

 boilers are very far superior to iron for marine purposes." And he gives 

 as one of his reasons " that copper is a better conductor of heat than 

 iron, and that if the advantages of encasing marine boilers with non- 

 conducting matter were properly considered and availed of, boilers 

 might be reduced in capacity, weight, and expense, to the obvious 

 account of the proprietor and to the increased stowage of fuel." 



Pridcaux also in his rudimentary treatise on Fuel, published this 

 year, states " That as the -conducting power of copper is to that of iron 

 as 2-1 to 1, a much smaller extent of heating surface and water space 

 suffice.'' 



Mr. Scott Russell might either have removed his difficulties by a 

 simple experiment, or have pretty safely concluded, from the almost 

 universal adoption of iron boilers, even for tlie longest voyages, where 



