292 ilr. X.u?iEK on the Evaporation of Water in Copper and Iron Vessek. "3 



if there really were any saving of space and fuel, this would not be the 

 case, that the efficiency of 3 to 2 was altogether an error. 



In order to satisfy myself, and perhaps others also, whether the 

 quantity of water evaporated followed the law of the conducting power 

 of the substances in which it was evaporated, (the foregoing quota- 

 tions being evidently based on this supposition,) I had a number of 

 vessels made of copper, iron, and lead, and the time which equal quan- 

 tities of water took to evaporate noted, and as if the preceding statements 

 were true, I certainly expected to find that the evaporation would be 

 completed in much less time in a thin copper vessel than in a thick lead 

 one. I was satisfied that the mode I adopted of conducting the experi- 

 ments, though rude, was sufficiently accurate to get at least a rough idea 

 of the subject. The vessels, five inches diameter and two and a-half 

 inches deep, were placed over a gas-burner, first with wire gauze be- 

 tween, and latterly without it, and the water evaporated to dryness. 

 The results are as follows : — 



Quantity of 



water boiled 



off. 



Iron vessel 

 ,'^ inch thick. 



Copper vessel 

 s.^^ inch thick. 



Iron sides J^, 

 & cop. hot ='j. 



Iron sides ,L, 

 & oop. hot H. 



Iron sides gW, 

 lead bottom H. 



Fluid, oz. 

 4 

 11 

 5J 



■1 



Min. 

 19 

 33 

 50 

 35 



Min. Sec. 



18 30 



30 45 

 44 



I think from this it is evident that the conducting power of the con- 

 tinuous metal has little or nothing to do with the quantity of water eva- 

 porated in a given time, any more than the thickness of the metal has to 

 do with it, as the same experiments prove. And therefore the universal 

 adoption of iron for steam boilers, is based no doubt upon well-grounded 

 experience, for iron is stronger and cheaper, is equally eflFective in 

 raising steam, and lasts, when well made, frequently till the fashion has 

 changed, and some better arrangement taken its place. 



As Peclet treats of the same subject in his " Traite de la Chalure," 

 and arrives at similar results, I have taken the liberty of introducing 

 some of his remarks. He comes to the conclusion that in the limits of 

 thickness generally employed, the nature and thickness of the metal are 

 without sensible influence. " For example,'' he says, " in the case of 

 steam boilers, at least for that part which does not receive the radiation 

 from the fire, I have not made direct experiments on this subject, but 

 the result of practice does not permit me to doubt that if the nature and 

 thickness of the metal have any influence it is very small, for it has been 

 long known that boilers of cast iron, of copper, and of malleable iron of 

 the same dimensions, but in which the metals have very various thickness, 

 give sensibly the same products in the same circumstances. This," he 

 adds, " is a fact upon which all engineers are agreed. We might besides 



