PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 605 



leakage from the boiler must be made up by using salt water in the boiler 

 It requires more tubing than the surface condenser. The apparatus now 

 known as the decalorator is an application of this principle. 



Mr. Maynard occupied the floor in replying to various questions relating 

 to the practical operation of the Pirson condenser. 



The following is an illustrated description of the Pirson condenser de- 

 scribed by Mr. Maynard: 



Fig. 1 is a side elevation; fig. II is a top view; fig. Ill is a longitudinal 

 vertical section. Figs. IV and V are views, showing variations in the 

 construction of the same apparatus. Fig. VI is a view of a surface con- 

 denser of common construction, and similar letters refer to similar parts 

 throughout, unless specially noted to the contrary. 



Figure VI exhibits the usual mode of construction. At a is a cluster of 

 pipes (that being generally the best form to resist pressure) inserted in 

 two flanges, b. The ends of these pipes are covered at c by a cap, and at d 

 by the channel in the bed-plate; at E is a tank to hold the water for con- 

 densing, which flows in and out, as indicated, being usually driven through 

 by a force-pump. At f is the exhaust pipe for conveying the steam to be 

 condensed, and g is the air pump. The steam is thus condensed, by coming 

 into contact with the cold surface of the metal, the pump g maintaining the 

 vacuity of the pipes, by removing the water as fast as it accumulates in 

 the channel d, and also any air or uncondensed gases. Hence the external 

 surfaces of the tubes are subjected to the pressure of the atmosphere, and 

 also to that of the column of water in which they are immersed, as before 

 named. This mode of condensing steam has those difficulties to contend 

 with, and which have hitherto been found insuperable, viz: the heating and 

 cooling of the metal pipes, consequent upon the periodic injections of the 

 steam, and of the action of the cold water, causes a continual alteration of 

 expansions and contractions; and these, together with the great pressure 

 upon them, soon produce fractures in the various joints and seams. When 

 such occur the vacuum can no longer be maintained, betause of the flowing 

 in of the air, and also of the water, which, of course, is fatal to the whole 

 operation. In addition to these defects, this system has another, resulting 

 from the fact that, as the wear of tubes so situated must be necessarily 

 rapid, the time must sooner or later arrive when, in consequence, merely, 

 of such wear, the condensing surfaces must give out. The moment at 

 which this will occur cannot be foreseen, but it will almost certainly take 

 place at a time when the continued working of the engine is particularly 

 needed — -as for instance, during a storm, since then the forces are most 

 energetically in operation, which tend to its destruction. 



Previous to the date of my invention, although many plans had been 

 devised for prolonging the wear, or lessening the liability of the condensing 

 surfaces to fracture, still none had been brought forward which claimed to 

 be able to continue the condensation and maintain the vacuum when such 

 fracture did occur. The ability to do this is the principal characteristic of 

 my invention; while in carrying that out it will be evident that some of 

 the forces which, in the old condensers, were most effective in causing 

 fractures, do not in mine exist at all, while others are exerted harmlessly. 



The nature of my invention may be stated, therefore, as consisting, 



