Polytechnic Association. 719 



between the flues is two and three-quarter inches in the clear. All the 

 flat water-spaces of the boiler are four inches wide, including thickness 

 of metal. The grate surface is thirty-eight and a half square feet. 

 The water-heating surface in the furnaces is 80.09 square feet ; in 

 the combustion chambers, 31.84 square feet ; in the lower flues, 

 428.70 square feet ; in the back connection, 76.92 square feet ; in the 

 upper flues, 587.48 square feet ; and in the front connection, 57.98 

 square feet ; making a total water-heating surface in the boiler of 

 1,263 square feet. The steam-superheating surface in the steam- 

 chimney is eighty-four square feet. 



The boiler, on the 2d of September last, was subjected, at 

 Hoboken, to a hydrostatic pressure of 112 pounds per square inch, 

 which broke a few of the braces without altering the form of the 

 semicircular top of the rectangular front. After being repaired, it 

 was again subjected, at Sandy-Hook, on the 4th of November last, to 

 a hydrostatic test of eighty-two pounds per square inch, without the 

 rupture of any part ; and on the following 15th of November, it was 

 subjected to a steam pressure of sixty pounds per square inch, without 

 fracture. 



In the experiment of the 22d of November, which we witnessed, 

 the fuel used was wood, and it was intended to burst the boiler by 

 steam-pressure under the condition of twelve inches of water above 

 the top of the flues, but it was found that the pressure could not be 

 raised above ninety-three pounds per square inch, owing to the exces- 

 sive leakage of steam from the seam joining the steam-chimney to 

 the boiler-shell. At the above pressure no fracture occurred, but the 

 form of the semicircular top of the rectangular front underwent a 

 change. The experiment was only of value in showing the strength 

 of a boiler of this type and construction after thirteen years' service 

 in a vessel. 



The next experiment was made on a rectangular box, built to repre- 

 sent the flat water-space or water-leg of the Westfielcl's boiler, recently 

 exploded at New York on board that vessel, with great destruction 

 of property and life. 



This box was six feet long, four feet high and four inches wide, 

 over all. The two side-plates were of the best flange fire-box iron, 

 five-sixteenths of an inch thick, manufactured by the " Abbott Iron 

 Company." The plates were held together by a single row of rivets 

 at their edges, passing through a frame made of wrought iron bars, 

 mitered at their ends, and having the same outside dimensions as the 

 box. These bars were three and three-eighths inches wide, two 



