MECHANICS AND USEFUL ARTS. 113 



steeple of St. Mary's Church; it was three-eighths of an inch thick origi- 

 nally, but had increased to seven-eighths of an inch with the rust. There 

 were several wedges used, and these had lifted the stones which they were 

 meant to keep in their places, and sonic of them had even been split by the 

 slow but certain force of rust expansion. The steeple was erected in 1756, 

 and the upper part had become so ruinous by these wedges, that it had to 

 be taken down by the city surveyor. 



Destructive Action of Oxides of Iron on Wood. M. Kuhlmann, at a recent 

 meeting of the French Academy, drew attention to the decay of the wood 

 of ships in the places adjoining iron nails and bolts; while no such decay 

 took place where wooden or copper bolts were employed. His observations 

 were made on ships at Dunkirk. For the purpose of explaining these facts, 

 he had instituted numerous experiments on the action of sesqui-oxide of 

 iron on various vegetable products, the results of which appear to prove 

 that the sesqui-oxide brings the oxygen of the atmosphere into contact 

 with the organic matter of the wood, and thus hastens its destruction. The 

 oxide becomes, in some degree, a kind of reservoir of oxygen, filling itself 

 at the expense of the air, and emptying itself to suppoi't the combustion 

 of combustible bodies. To avoid this injury to the wood of ships, the nails 

 etc. should either be coated with zinc, or made of copper. 



ON THE STRENGTH OF IRON AND STEEL. 



At the meeting of the British Association for 18-39, Prof. Macquorn gave 

 an abstract of a set of experiments conducted by Robert Napier and Son, 

 (the eminent engineers) of Glasgow, to test the strength of iron and steel 

 bars and plates. The following are the most important results arrived 

 at, arranged in a tabular form, the weights in each case being applied 

 gradually. 



TABLE A IRON BARS. TABLE B IRON PLATES. 



Tenacity] Tenacity 



Districts. in Ibs. Districts. in Ibs. 



per sq. in. | per sq. in. 

 Yorkshire, strongest, 62,886 Yorkshire, strongest crosswise, 50,515 



weakest, 60,075 



" forged, 66,392 



weakest, " 46,221 



TABLE C STEEL BARS. 



Staffordshire, strongest, 62,231 Steel for tools, rivets, etc., 



weakest, 56,715 



West of Scotland, strongest, 64,795 



" weakest, 65,655 



Sweden, strongest, 48,232 



" weakest, 47,855 



Russia, strongest, 56,805 



" weakest, 49,564 



strongest, 132.909 



" weakest, 101,151 



Steel for other purposes, 



" strongest, 92.015 



" weakest, 71,486 



TABLE D STEEL PLATES. 

 Strongest lengthwise, 94.2S9 



TABLE B IRON PLATES. Weakest lengthwise, 75,C94 



Yorkshire, strongest lenghthwise, 56,005 Strongest crosswise, 96.308 



" weakest, 52,000 ' Weakest crosswise, 69,082 



NOTE. The strongest lengthwise is the weakest crosswise, and vice versa. 



ON THE USE OF PINE AS AN ORNAMENTAL WOOD. 



In the royal palace at Potsdam there is a suite of apartments, the whole 

 wood-work of which, as well as the standing furniture, consists of yellow 

 deal, not painted, but polished, and exhibiting the natural color and grain 



10* 



