644 TRANSACTIONS OP SECTION G. 



Class 1 gives very cheap steam, as capital charges are debited to other 

 pur]Mses, but is not applicable to ordinary or average steam plants. 



Class 2 only applicable when fuel is extremely cheap. 



Class 3. When the gas is proiduced only for steam boilers ; it is only 

 applicable to boilers of the Bone-Court type. 



Cla.S'S 4. This is hardly a gas-producer at all, but is named because many 

 attempts have been made in this direction. It fails mainly by reason of 

 destruction of brickwork under the intense heat. 



Class 5. In this class is the Mills furnace. 



All the above, as compared with the ordinary internal fire, have the 

 advantage of not arresting the combustion process by temperature-reduction 

 through contact with water-cooled plates. 



Single gas-producers for metallurgical furnaces are v/ell known and successful. 



The aims of the inventor of the Mills furnace were : 



1. It should not be too costly. 



2. It must utilise the radiant heat of combustion. 



7t. There must be ample temperature to ensure complete chemical com- 

 bination. 



4. Access to boiler for examination and repairs must not be hindered. 



5. The whole of the various gases given off by the fuel must be immedi- 



ately burnt with their sensible heat of production in them. 



6. Little or no excess air must be used. 



7. All ordinary qualities of coal must be usable. 



8. Attendance must not be excessive. 



Dealing first with No. 6, above the usual allowance of excess air is absolutely 

 necessary in the burning of fuel in solid or lump form by reason mainly of the 

 mechanical difficulty of bringing each part of oxygen into intimate contact with 

 its concomitant part of carbon or hydrogen at the right time and in the right 

 place. 



To do this in a metal water-surrounded box is an impossibility. 



Slides showing outside, inside, and sectional views of the Mills producer 

 will be shown. The action and control of the induced draught giving the 

 separate air supplies for gas production and its combustion, the cellular con- 

 struction of the roof and walls by which air for combustion is heated by the 

 otherwise lost radiant heat of the producer ; the means of withdrawing the 

 whole to allow access to the boiler front ; the special design of firebrick gas-and- 

 air-mixing device and burner ; the self-cleaning sight-hole appliance ; the auto- 

 matic fuel-feed ; the arrangements for clinker-extraction ; the flue-gas inter- 

 ceptors introduced, and other details of construction are shown on the slides, 

 and examples and models of various parts will be on view. 



The results of tests on a Cornish boiler, worked on an ordinary internal fire 

 and with the Mills producer, with the same fuel in each case, and tested by the 

 same expert, show a saving of about 50 per cent., and there was no smoke. 



Tests on a Lancashire boiler with the Mills producer give high efficiencies 

 and standardised evaporations ranging from 10'23 lb. to 11"47 lb. of steam from 

 1 lb. coal, and on a comparison with another boiler fired with the same fuel 

 but with the ordinary internal fire, the tests show a saving of about 18 per 

 cent, in evaporation. In this case also there was an entire absence of smoke. 



FRIDAY, SEPTEMBER 10. 

 The following Papers were read : — 



1, The Heating of Iron when Magnetised at very High Freqtiencies. 

 By N. W. McLachlan, B.Sc, Eng."- 



This paper described experiments illustrating the heat produced when iron 

 is magnetised by very high-frequency alteniating currents, e.g., 2x10' to 

 5x10^ periods per second. 



' See The Electrician, vol. Ixxv., p.. 877. 



