PROCEEDINQS OP THE POLYTECHNIC ASSOCIATION. 603 



1st. With surface condenser, feeding fresh, water to the boilers : 



Average running time '.'. 12 days 164 hours. 



Coal consumed 420 tons. 



Oil expended 56 gallons. 



Tallow 43 lbs. 



2d. With the jet condenser and salt watdr feed : 



Average running time 13 days 21 hours. 



Coal consumed 471 tons. 



Oil expended 78 gallons. 



Tallow 125 lbs. 



As the steamer made twenty trips per annum, it will be apparent that 

 the inci'eased expenses of the jet over the surface condenser would be : In 

 time, twenty-four days ; in coal, 1,020 tons ; in oil, 440 gallons ; in tallow, 

 1,640 lbs. The money value of which at the time was as follows : 



1,020 tons of coal, at $25 $25,500 



440 gallons of oil, at $1.90 836 



1,640 lbs. of tallow, at 12^0 205 



Boarding 300 passengers, twenty-four days, at $1.00 7,200 



Total $33,741 



The vacuum on the Sonera averaged 26 inches by the mercurial gauge, 

 with the water at 142 deg. F. for twelve days consecutively in the month 

 of June. 



The improvements on Hall's condenser have been fully illustrated before 

 this association. It is now proposed to examine more minutely the defects 

 common to all, and the manner in which they can be completely obviated. 

 The chief difficulty to be contended with in such condensers is the con- 

 tinued contraction or expansion of the tube within the condenser, arising 

 from the changing of temperature, by injection of steam and cold water; 

 this added to the weight which the tubes must sustain, produces fractures 

 in the various joints and seams. The wear of the tubes must be necessa- 

 rily rapid, and 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 particu- 

 larl}'- needed, as for instance, during a storm, since then the forces are most 

 energetically in operation, which lead to its destruction. 



The surface condenser in the ocean steamer the British Queen, gave out 

 in a gale, causing for a time the stoppage of the engine; the vessel, how- 

 ever, was saved. Some eminent engineers entertain the opinion that the 

 loss of the President must have been from the disabling of her surface con- 

 denser. The apparatus to be described remedies the defects mentioned. 

 It consists in enclosing the surface condenser within a tank or vessel, 

 which shall be so constructed as to be capable of serving as an ordinary 

 jet condenser, when any derangement of the tubes or other condensing sur- 

 face proper shall require it, thereby affording an alternative which shall 

 secure the continuity of the vacuum, though, of course, at the expense of 

 the loss of the whole or a part of the fresh water afforded by the surface 

 condenser when in perfect order. Another highly important feature in this 



