324 Review of Renwick 



After principles have been studied in the abstract, we love to see 

 them brought into near connexion with the arts which they illustrate, 

 and we renew our acquaintance with them with increased pleasure, 

 when we recognise tliem in their useful applications. 



The article on Combustion, in the second chapter,, is particularly 

 worthy of attention ; and we know not where to find, within the same 

 compass, more useful information on this important subject, not mere- 

 ly in reference to the Steam Engine, but to the ordinary purposes 

 of hfe. 



We do not propose to follow our author through all parts of his 

 work, but shall have chiefly in view those parts which are at present 

 peculiarly interesting to the community, namely, the means of secur- 

 ing safety in the use of the Steam Engine. 



The dangers of the Steam Engine are obviously of a twofold char- 

 acter, — such as result from defective construction of the machinery, 

 and such as arise from the peculiar nature of the moving force. The 

 work before us begins with the consideration of the former, particu- 

 larly as it relates to the construction of boilers. We subjoin an ex- 

 tract on the materials of boilers. 



Boilers are always of metal, and three different materials are used 

 in their construction: wrought iron, cast iron, and copper. Wrought 

 iron and copper are rolled for this purpose into plates and sheets, 

 which, after being bent to the proper form, are united by bolts, driven 

 through holes punched around their edges, and riveted. When cast 

 iron is used for boilers, they may either be of a single piece, or it 

 may be cast in separate portions, which are united by screw bolts and 

 nuts, passing through holes left or drilled in Haunches. Of the two 

 first, copper is most easily worked, but it is by far the most expensive 

 material, and is therefore now used only in a few instances, where the 

 others are, from the circumstances of the case, inadmissible. Copper 

 is much less easily acted on by oxygen, than sheet iron ; it acts 

 less powerfully on. the saline deposits, that occur when sea or other 

 impure water is used ; in addition, it*is less liable, than either of the- 

 other materials, to split or. crack on sudden changes of temperature. 

 Sheet iron is more tenacious than copper, but is liable to rapid oxida- 

 tion, and has frequently invisible joints arising from the manner in 

 which it is manufactured. Stijl, however, when the water used is 

 tolerably pure, it is the best material,.if we take into view the strength 

 and compararive cheapness. — p. 67, 



