42 On Mr. Arthur PFooIf's improved Apparatus, 



furnace S,S,S, through which the flame first passes, and re- 

 ceive its direct action, which it does over nearly a half of 

 its surface, as may be seen by looking at the vertical section 

 ASS, fig. 6. The smaller cylinders have a communication 

 with the main cyhnder in the following manner : — Ihree 

 cylinders, CCC, are placed parallel to the main cylinder A, 

 over the part of the furnace by which the flame returns, in 

 such a manner that each of the cylinders C C C takes in three 

 ot the smaller cylinders a an, being' united to and con- 

 nected with them as shown in fig. 4, which is a longitu- 

 dinal vertical section of that part of the apparatus. The 

 cylinders CCC have a direct communication witli tne main 

 cylinder A by the pipes or tubes PPP, as may be better 

 seen by the cross vertical section, fig. 6, in which the same 

 parts are marked with the same letters as in figures 3 and 4. 

 The three tubes CCC are preferred to one lon^ tube, to pie- 

 vent any derangement taking place in the furnuce or in ihe 

 tubes, by the expansion and contraction, occasioned by 

 changes of temperature, which is more considerable lu one 

 tube of the whole length of the furnace than when divided 

 into three portions ; and it is for the same reason tha: *he 

 tube A IS not made to communicate dh'ectly with the smaller 

 tubes aaa, but mediately by means of the tubes marked 

 C and P. — N.B. The two outermost of the tubes marked P, 

 instead of eoing parallel to the middle tube P, may both be 

 inclined towards it, as one of them is from v>, so as to join 

 the cylinder A near the middle ; or any other direction may 

 be given to them, to prevent derangement by expansion. 



Ihe tubes C and a are kept from separating by boii.- from 

 the inside of a passing through the top of C, where they 

 are secured by nuts screwed on to them (see fig. 5.); and 

 these parts of C are so contrived, that by takinir otTany of 

 the nuts a cover may be reirovcd, and a hole presented 

 large enough to admit a man's hand into C to clean it out. 

 Fig. 5 is a longitudinal vertical section of the boiler and 

 furnace, through the centre of the axis of the main cylin- 

 der A, showing the course which the flame and heated air 

 are forced to take. The first three small cylinders are com- 

 pletely surrounded with flame, being directly over the fire ; 

 the flame is stopped by the brick-work W over tiie. fifth, and 

 forced to pass under it, and then over the sixth, where it 

 again meets with an interrui)tion, which forces it to go under 

 the seventh, over the eighth, and partly over partly under 

 the ninth. It then turns round the end of the longitudinal 

 \vall which divides the furnace, and passes over the eighth 

 smaller cylinder, under the seventh, and so on alternately 



over 



