TAcnTM PA>-s. 349 



The foregoing plates, Xos. XXX^^^ and XXX IX, represent two 

 styles of vacuum pans manufactured by the Colwell Iron- Works, and 

 the following description of the details of their construction, and the 

 mode of their operation has been supplied by the manufacturer: 



Vacuum pans are of copjier or iron. Copper was once used ex- 

 clusively, but of late years cast-iron has been the choice. 



The heating surface is of seamless drawn copper tubes, in serpentine 

 coils, leaving from three to four inches space between each circle, and 

 inclining to the center, the lower coil following the dip of the bottom, 

 and the upper coil having a dip of about four inches, taking steam on 

 the outside, and leading the condensation out at the center through the 

 bottom to traps — the diameter of tubes depending upon the size of pan. 



These coils are secured to cast braces by a cup and cover, which hold 

 them securely from jumping during the boiling, yet allowing them to 

 expand and contract without any strain. The braces are so arranged 

 that they offer but little obstruction to the outflow of the finished 

 sugar (this is a late improvement). Heretofore it was clumsy and 

 strong, or light and weak — in the first place, holding great masses of 

 magma at each strike of the pan ; or, in the latter case, when a very 

 stiff boiling is made, the worms were oftimes in a ruin at the bottom 

 of the pan. With our arrangements, the minimum of obstruction and 

 the maximum of strength are obtained. The heating surface is the 

 life of the pan, and if not properly arranged, properly secured, with 

 proper inlets and outlets, the amount of work will not be up to expec- 

 tation. 



Mountings. 



Double steam valves, through which the steam is admitted into the 

 coils — principally exhaust steam. That not being enough, live steam 

 can be used at the same time, and yet not exert any back pressure 

 up>u the exhaust of the different engines, if properly managed. 



Eye glasses, which are placed in curb and dome to see the depth of 

 liquor, as well as the action of boiling. 



Thermometer, vacuum guage, which, to be the most accurate, should 

 be columns of mercury. A double-charge cock, with one pipe leading 

 to the syrup tank, and another leading to molasses tanks. 



A butter or oQ cup, for the introduction of a little oil or sweet but- 

 ter to check the foaming. 



The charge cock has a small cock in its side, called the lime-water 

 cock, for the purpose of correcting any acidity that may occur. 



The draw off valve at the bottom is made much larger than for- 

 merly, as refiners and planters find it much more economical to boil 

 the pan as stiff as it can be done without getting it too dry (in which 



