ON ATLANTIC STEAM NAVIGATION. 27 



marine boilers on long voyages, are liable to form erroneous notions of the accumulation of soot 

 and its consequences. In the first place, soot cannot exist in the furnaces, when the plates 

 of which they are formed, with the best management, are constantly giving out from the 

 intense heat they sustain. The accumulation in the flues is principally on the bottoms, as will 

 presently be shown. The chimney or funnel never absolutely requires to be swept, even in 

 the worst cases of draught. In some vessels the practice is resorted to simply as a matter of 

 course : in the 'African' it was never done, except to prevent the dust from falling on those 

 repairing the flues immediately beneath, when it was previously beaten only on the outside for 

 that purpose : again, the vessels in the Mediterranean packet service are never detained on 

 their voyage of 1000 miles, no matter how long the time occupied thereon, to sweep 

 the flues. 



The 'African' eight or nine years since, when in the colonial service, made the passage from 

 England to Malta direct, nearly 2000 miles. On the third day after her departure a fair wind 

 sprang up, the wheels were unconnected, and the vessel put under canvass : it was thought a 

 favourable opportunity of setting the machinery in order; the flues were swept at the same 

 time, in order to profit by any advantage arising therefrom : after having sailed two days, they 

 proceeded by steam at full power and fine weather for the nine succeeding days, at the end of 

 which time no lack of steam was apparent. And recently she went from Malta to Alexandria, 

 820 miles, thence to Beyrout, 320 miles, back to Alexandria, and thence to Malta, without 

 sweeping the flues, a distance of 2200 miles ; the necessity of arriving at Malta with the 

 Indian mails, preventing the vessel from remaining a sufficient time at either of the posts for 

 the purpose of sweeping the flues. 



The sweeping of the flues consists simply in removing the soot and burnt fuel carried over 

 by the draught from the lower part of the flues ; the upper portions, which are available for 

 steam generation, having merely a thin coating of soot, which by no means amounts to 

 a formidable non-conductor. 



After the long voyage of the 'African' above alluded to, I was curious to know the condition 

 of the flues, more particularly as the steam was generated in abundance, without any apparent 

 increase either of labour or fuel, immediately before arrival ; a blue lambent flame (carbonic 

 oxide) constantly appearing some feet above the chimney, as was usual after being a day or 

 two under weigh : it appeared that the flame had reverberated downwards, so as to act on the 

 lower parts of the first or main flue of each boiler : the soot was deposited on the bottoms of 

 the other flues to a greater extent ; and beneath the chimney, the soot was swept, so as to leave 

 an opening about one foot clear, out of 4 feet 6 inches, the entire depth of flue ; the voyage 

 having occupied, with stoppages at Alexandria and Beyrout, about twenty days. 



Shortly afterwards, a voyage was made from Malta to Corfu, of between four and five days; 

 the flues were then swept, and, to my surprise, as much soot was withdrawn as on the occasion 

 last described : it then became quite evident, that after a certain quantity of fine cinder and 

 soot had been carried over and deposited, the surface, being swept by the flame and heated 

 air, was rendered so light as to be carried up the chimney, and driven away at the same rate 

 as its formation ; and this conclusion was confirmed by the quantity of burnt soot which was 

 strewed over the decks, at night in particular, after the awnings were furled, being sensibly 

 crushed by the feet on pacing the decks. Again, having examined the flues of the same vessel, 

 after being employed on experiments, &c. for twenty-five days, during the months of June and 



