SIR WILLIAM SIEMENS, F.R.S. 151 



become of great value in the colonies for evaporating cane juice, 

 principally on account of the simplicity of the arrangement. The 

 L r ivut, loss and deterioration consequent on the high temperature to 

 which cane juice must be exposed for evaporating it on the old 

 system in open pans are well known, and many ingenious plans 

 li;t\' IHVII invented and to some extent worked for evaporating at 

 lo\v temperatures ; but, on account of the improved plans being 

 i-itlitT very much more costly or requiring much more skilled 

 attention to work them, the greater part of the sugar produced is 

 still made on the old and wasteful plan. Of all the contrivances 

 fur evaporating at low temperatures the ordinary vacuum pan 

 exhausted by pumps is at present the best, when carefully designed ; 

 and in it under favourable circumstances very rapid evaporation 

 can be produced at low temperatures. In the sugar-growing 

 colonies however almost every circumstance is unfavourable for 

 this mode of working ; the water required for condensing the 

 vapour from the evaporating pan is warm, and consequently must 

 be used in large quantities, thereby necessitating large pumps for 

 its removal, and for exhausting the pan ; the pumps and motive 

 power thus form together with the pan a very costly apparatus, 

 which requires a considerable amount of skilled attention, often 

 not obtainable, and frequent repairs. 



On the contrary, a vacuum pan exhausted by the steam jet 

 exhauster in the manner shown in Figs. 15 and 16, Plate 29, 

 becomes a very simple apparatus, only requiring a supply of steam 

 at a moderate pressure for the jet A, which exhausts the vapour 

 given off by the boiling solution of sugar or other liquid in the 

 pan B ; and the steam and vapour together are then passed through 

 the heating tubes D of the pan, thereby producing evaporation. 

 The area of the steam jet is regulated by the hand-wheel C, the 

 steam being supplied by the pipe E ; and the course of the current 

 of steam and vapour is indicated by the arrows. By this arrange- 

 ment the costly vacuum pumps and the steam-engine or other 

 motive power are dispensed with, as well as the condenser and its 

 supply of condensing water, the latter being in many places a 

 consideration of vital importance ; and in their stead is sub- 

 stituted the steam-jet exhauster, a comparatively cheap and simple 

 apparatus, requiring little or no attention, and not liable to get 

 out of order. 



