44 ANNUAL OF SCIENTIFIC DISCOVERY. 



strain on the circular scams. This is an important practical distinction, be- 

 cause it is clear that, to insure uniform working strength, the longitudinal 

 seams must be doubly fortified; and, in the consideration of the means of 

 soldering, four distinct kinds of riveted joints are compared, and their rela- 

 tive strengths determined from actual trials. Welded joints are likewise 

 discussed, and should the reported results of their capabilities to resist burst- 

 ing strains be corroborated by advanced experience, they promise to super- 

 sede riveting, if not entirely, at all events for the principal joints. In the 

 order of tensile strength the joints are ranged thus : 



1. Scarf-welded joint, .... 100 



2. Double-riveted double-welt joint, . . 80 per cent. 



3. Double-riveted lap-joint, ... 72 " 



4. Lap- welded joint, .... 66 " 



5. Double-iiveted single-welt joint, . . 65 



6. Single-riveted lap-joint, .... 60 " 



In this comparative statement the strength of the entire plate is repre- 

 sented by 100; and the trials were made with plates varying from | to ^ 

 inch in thickness. The relative strength of single and double-riveted joints 

 do not very materially differ from those deduced by Mr. Fairbairn. London 

 Artisan, Dec. 1858. 



ON THE USE OF SUPERHEATED STEAM. 



At a recent meeting of the Society of Mechanical Engineers, London, the 

 President, Mr. Power, stated that, as the result of extensive experimentation, 

 he had arrived at the conclusion that an advantage can be derived from the 

 use of superheated steam, amounting to an economy of fuel of from twenty 

 to thirty per cent, in marine engines, and that a moderate extent of super- 

 heating enables all the important advantages of the plan to be obtained. 

 By so doing, there is nothing objectionable involved from extra tear and 

 Avear, complication of apparatus, or difficulty in lubrication. The real ad- 

 vantage in superheating the steam appeared to be in preventing the presence 

 of water in the cylinder of the engine, thus insuring pure steam to work the 

 piston, making it a real steam-engine, and not a working mixture of water 

 and steam. In all condensing engines, the interior of the cylinder being 

 open to the condenser during half the time of each revolution, the tempera- 

 ture of the cylinder is reduced to about 125. When the steam is therefore 

 admitted for the next stroke at a temperature of 260 Fah., it is robbed of 

 considerable heat, and a quantity of water is thereby formed in the cylinder. 

 A portion of this water may be evaporated again towards the end of the 

 stroke by carrying the expansion down to a low pressure, but its effective 

 value is lost during all the previous portion of the stroke. If, therefore, as 

 much heat is added to common steam by superheating it before entering the 

 cylinder as will supply the amount which is usually abstracted from it, not 

 a drop of water is formed during the whole stroke; it remains dry steam to 

 the end. The addition of 100 of heat to the temperature of steam insured 

 the desired object with steam at twenty pounds pressure on the square inch, 

 as used in marine engines. 



THE UNIT OF HEAT. 



Professor Rankine, at the late meeting of the Institution of Engineers of 

 Scotland, observed : " I am happy to recognize evidence that the true princi- 



