TRANSACTIONS OF THE SECTIONS. 231 



pan, to which the tubes arc riveted, is a cast-iron steam chest, with stops, to ensure 

 a circulation of the steam through the tubes in a serpentine manner. Between these 

 tubes a series of copper discs is made to revolve, the diameter of which is 3 feet, and 

 the thickness about \ih of an inch. 



The condensed water from the tubes, caused by the evaporation of the liquid in 

 the pan, is received in an ordinary condensing box, fitted with a ball and valve, and is 

 thence conveyed to a receiver, ready for readmission to the boiler at a temperature 

 of 160" or 170° Fahr., according to that of the liquid under evaporation. 



This method affords the means of evaporating syrups and other liquids at a tem- 

 perature under 180°, at which temperature sugar will not carbonize. 



The economy of fuel in this process is very great, while evaporation is as rapid as 

 when the vacuum pan is employed. The cost of the latter (the method of work- 

 ing it requiring skilled labour of a superior degree) is such, as to place it out of 

 the reach of most proprietors in the colonies, whilst the cost of this pan is trifling, 

 and may be worked by an ordinary boiler-man. For the revolutions of the discs 

 little power is required, as they are supported upon centre bearings, and may be 

 turned by manual or any other motive power. 



Every part of the machinery is open to view, and from its extreme simplicity can be 

 cleaned, or any accidental injury repaired by a common workman. One great ad- 

 vantage to be derived from the use of this apparatus is the facility it affords for 

 working up molasses, and thus converting the second product into an article almost 

 equal to that of the first. 



On the Engines of the 'Callao,' 'Lima,' and ' Bogota' By J. Elder. 



In these engines the steam enters at 42 lbs., and is expanded to nine times, or to 

 4f- lbs., namely, from 42 lbs. to 14 lbs. in the small cylinder ; it then enters the large 

 cylinder at 14 lbs., and is expanded to 4f lbs. ; but as the second piston is three times 

 the size of the first, the gross load will be the same on both pistons, and the piston 

 rods, crossheads, and connecting rods may be duplicates of each other. 



From the above pressures of steam at the entering of the cylinder, it is evident 

 that, unless the inside surface of the large cylinder is retained about 210°, condensa- 

 tion of the steam on entering is certain, and such condensation will chiefly evaporate 

 into the condenser while the eduction port is open, and the latent heat necessary to 

 evaporate such condensation will be much greater than what would have radiated 

 from the hot cylinder to the condenser, had no condensation taken place ; and such 

 heat would be entirely lost. In the same manner it might be mentioned, that the 

 inside surface of the small cylinder should be retained as high in temperature as the 

 steam that enttrs it ; and in order to attain this object, every effort should be made 

 in the construction of steam machinery. It is evident, that, for the small cylinder, 

 superheated steam is absolutely necessary for this purpose, either in the jackets or 

 cylinder; and in the large cylinder the temperature of steam direct from the boiler 

 to the cylinder may be sufficient, if communicated through a pipe or aperture large 

 enough. 



In the engines under description, the pipe supplying steam to the jackets was 

 2-j in. diameter, and the steam was superheated to upwards of 400 degrees that en- 

 tered the jacket. It was found that a large supply to the jacket saved a vast quan- 

 tity of heat, which can only be explained by the principles above mentioned, namely 

 that any quantity of heat supplied to the jackets assisted in proportion to the quan- 

 tity of latent heat it saved being evaporated to the condenser during the eduction of 

 the steam ; and if the pipes to the jackets were large enough, or sufficient to prevent 

 the condensation referred to, the economy of the machinery was realized to the 

 greatest extent. 



The writer begs to call the attention of all parties concerned, to the performance 

 of Cornish pumping-engines, and more particularly to the similarity of action of the 

 steam-jacket in these engines to the principle of that of the double-cylinder engine 

 with steam-jackets. In the Cornish engine the piston is single-acting, and the jacket 

 has twice the time to do its work, or rather the steam in the cylinder is twice the 

 time in contact with the jackets that it is generally with Watts' engine ; so that 

 the Cornish engines have very large jacket surfaces in proportion to the power deve- 



