ADDITIONAL OBSERVATIONS AND GENERAL REMARKS. 



20. ENOUGH has been stated to show that muriate of soda is crystallised subsequently 

 to the deposition of the sulphate of lime ; and from further observations, I conclude that the 

 sulphate of lime will deposit and indurate at any temperature from 212 upwards, and at any 

 degree of concentration ; the more limited this is, of course the less deposit ; so that a person 

 having the care of marine engines on a station cannot be too much on the alert to meet the various 

 mechanical difficulties which may interfere with prescribed arrangements for the good conduct 

 of the boilers ; which arrangements are not always disposed so as to effect the desired 

 purpose, particularly when boilers are composed of many parts. Engineers do not give that 

 attention, at all times, to the due circulation of the water in the respective boilers, which their 

 necessities require : not unfrequently I have known three or more boilers communicating 

 freely above the furnaces, and by side pipes beneath : the pipes often become choked ; 

 consequently in blowing off the front boiler, the water equally descends in the whole, the 

 after-boilers yielding their quota from the surface, (where they communicate freely,) while the 

 earthy matters, and common salt even, are permitted to subside in receptacles whence they 

 cannot be removed. 



If there were even three or more cocks in such case, it would not be possible, day and night, 

 nor would it be safe, to open all at the same time ; and if one boiler is blown off at the end 

 of two hours, as recommended, each boiler remains six hours before the operation is repeated. 

 The descent of the water should be equal and simultaneous from all the joining boilers 

 if possible; which, if not effected, will often permit one boiler to be perfectly clean, whilst its 

 neighbour is thickly incrusted. Very recent examples of the neglect of proper arrangements 

 for circulation of the water in the respective boilers, and of injury thereby sustained, have 

 induced me rather to enlarge on this matter; but still I fear that nothing but the use of 

 distilled water will ever thoroughly obviate the evils to which marine boilers are subject on 

 very long voyages, although at the end of five or six years in active employ a copper boiler 

 may not be liable to injury if properly attended to; while it is notorious that the fire-places 

 of iron boilers of similar construction, employed between Falmouth and Corfu, require repair, 

 almost invariably, at the conclusion of every voyage. I believe that four voyages to the 

 Straits are the most that have been made prior to a general repair of the boilers. 



I have stated that the African was three years employed before it was deemed necessary to 

 detach the scales : on the sides this is extremely difficult to manage, the waterways seldom 

 exceeding four inches, and rarely being so wide. 



I was led to imagine, from the appearance of the boilers after the first voyage, that they 

 could have been employed indefinitely without any considerable scale ; but experience has 

 shown, that to a certain extent it must be expected : in the sixth year, the vessel being 

 actively employed in the Mediterranean, the boilers were scaled about once in three months ; 

 the number of entire days at sea in that time being from sixty to seventy. The tops of 

 the tubes were not always cleaned, attention being paid to remove all scales that might be 

 partially detached from the sides : no time was wasted in removing the scales by scraping or 

 chiselling them in minute portions, the loose or easily detached pieces only being attended to. 



The sides of the fire-places have seldom more than patches adhering to them here and 



b 



