FeOCEEDIXGS of the rOLYTECHNIC ASSOCIATIOX. 961 



to one-tenth of tlie heat in tlie stt^iini supplied l)j tlie l)oi!er. Theai, 

 again, the huiler does not seem to transfer to the water all tlie heat 

 evolved by the combustion of the fuel. In this direction the method 

 of saving is better understood. A l)oiler with sliort tubes and quick 

 draft will furnish a given power at a certain cost in fuel. Now, in. 

 order to save a small quantity of fuel, the size of the boiler has to be 

 greatly increased; hence there are in ])ractice boilers constructed with 

 great variations in their proportions, but the economy of each can, 

 by simple calculation, be detormined with great accuracy by the 

 skilled engineer. 



Mr. J. K. Fisher said he thought the l)oilers more at fault that the 

 engines in regard to economy. In Europe the steam boiler is much 

 more advanced than it is hei'c ; we have been crowding into boilers 

 a vast amount of heating surface, yet it appears by the experiments 

 of various engineers, that the loss of heat from various causes amounts 

 to twelve per cent as a minimum, and liftj'-four per cent as a maxi- 

 mum, so that al)Out one-fourth of the heat is only utilized. 



Adjourned for two weeks. 



January 27, 1870. 



Prof. S. D. Tillman in the chair ; C. E. Emeiit, Esq., Secretarj'. 

 Temperiisg Steel. 



Professor J. Phin said that there was hardly a subject in the arts 

 more important than that of tenq)ering steel. The difficulties in tem- 

 pering steel properlj' are not met with in small articles, but mostly 

 when large masses of it are to be treated. It is laid down as a rule 

 by writers on the hardening and tempering of steel, that all bright 

 steel requires a coating of some kind before putting it into the water, 

 more particularly when the article to be hardened is of large size. If 

 this is not done it is very liable to crack. This is shown in the case' 

 of common turning tools, which if hardened with tlie external skin 

 left by the action of the hammer in shaping them, will always stand 

 and keep a liner and more certain edge than if ground l)efore harden- 

 ini;; the precaution being taken to heat the steel to the exact tem- 

 ])erature re(|uired \o bring it when cooled to the desired hardness 

 M'ithout subsequent tempering. Mr. lleid, of Woolwick, has recently 

 written a very able work on this subject, but lie did not touch on the- 

 method about to be described. It has long been known that certaia. 



[Ln-st.] CI 



