MECHANICS AXD USEFUL ARTS. 51 



Starch- Sugar, Molasses, Syrup.' Gunion. put into a boiler, seventeen and 

 a half feet long, and three and a half feet in diameter, five kilogrammes 

 of molasses every two months ; he found that this completely prevented 

 incrustation. 



Guimet proved the advantage of this process, but employed brown 

 starch syrup, three pounds every six months for a boiler of eight-horse 

 power. 



Tin salt (chloride of tin) is recommended by Delandre ; it is similar in 

 its action to muriate of ammonia ; but as it is cheaper it is to be preferred. 



Soda and potash have been recommended by Kuhlmann, and more 

 recently by Fresenius. According to the latter, the property of forming 

 crust occurs more with water containing gypsum than with that contain- 

 ing chalk. 



Kuhlmann recommended the addition of 100 to 130 grms. of soda 

 monthly, to every horse-power with water containing sulphate of lime. 

 Eisner observes that too much soda might injure the solderings and joints. 

 Zimmer, of Frankfort, who long employed this method, found that the 

 boiler was strongly acted upon ; he ascribes this to the presence in almost 

 all sodas of cyanide of sodium, which possesses the power of dissolving 

 iron. Scientific American. 



NEW FORM OF SUSPENSION BRIDGE. 



At a recent meeting of the Franklin Institute, Mr. "William Reed ex- 

 hibited a model of an improved form of suspension bridge. He forms a 

 hollow, truss-beam of plate iron, with cast-iron ends the whole length of 

 the span. In this, the wire is suspended from the upper end of each 

 extremity, and passing towards the lower margin, near the centre, the 

 cable and tube being well supported by truss braces, which effect the 

 double purpose of bringing the weight of the truss, and the superstructure 

 of the span, on to the cables, and holding the truss-beam in proper shape, 

 acting as the ribs to a vessel. The height of the truss-beam, and the 

 thickness of the iron of which it is made, are to be governed by the 

 length of the span. The upper part of the truss-beam must contain suffi- 

 cient material, to resist the compression of the superstructure and load, 

 and the two feet of the lower edge of the truss-beams, with the cables, 

 are to support the whole tension. Where the span is long, and breadth 

 of beam is required, in order to save material, the top, and two feet of the 

 lower edge of the beam, may be made of plate iron, and the intermediate 

 space filled in with wrought iron bars, riveted from the top to the bottom, 

 crossing each other, forming a lattice so as to preserve the stiffness of the 

 tube or beam. Where footways are wanted, the floor-beams can be ex- 

 tended out for that purpose. By this arrangement, the whole amount of 

 the tension of the wire can be obtained, while the peculiar form of the 

 truss-beam will cause any weight that may be brought on any part of 

 the bridge, to communicate to all parts of the span. 



