ON MARINE BOILERS. 3 



necessary to be withdrawn, four-fifths being the amount required to be evaporated for the 

 supply of the engines. It having been before observed that the water evaporated is fresh or 

 distilled water, that remaining being specifically heavier than sea water in proportion to the 

 quantity evaporated, it is evident that without a change the saturation would increase till the 

 boiler became a common salt pan. The operation of the brine pump however maintained 

 the water uniformly at about 226, at 2| Ibs. pressure per square inch ; at which temperature 

 it contained -/^ of its bulk of salt : hence, as much salt was extracted by the pump, in a 

 gallon of brine, at -/$ concentration, as was injected by the feed pump in 5 gallons of sea water 

 containing ^ salt : thus maintaining the condition required, which being within the prescribed 

 limits of saturation, viz. 232, sulphate of lime only could be deposited ; but at this period 

 the deposition of muriate of soda was the evil sought to be averted, and this arrangement 

 did it effectually. The lime remains to be considered, of which more hereafter. The brine 

 pump has given place to the indefinite operation of blowing out ; but, from my knowledge 

 of its advantages at sea, I should recommend its use in all land engines where fresh water 

 cannot be obtained ; an opportunity being afforded of recovering nearly all the heat abstracted 

 from the boilers with the water thus withdrawn. 



5. The incrusted state of the boilers, to which I have referred, appeared at variance with 

 observations made by me in the North Sea, Channel, &c. on the influence of sea water on the 

 interior of marine boilers. To determine the fact, I carefully noted the degree of saturation 

 of the water of the boilers at various periods each day, as indicated by Fahrenheit's thermo- 

 meter immersed in a portion drawn therefrom, and boiling under the pressure of the atmo- 

 sphere, on my first voyage, in 1831, from Falmouth to the Mediterranean and back; the 

 result of which was, that having blown out a portion of water from the boilers (which were of 

 copper) every two hours during the passage, they were on each successive examination found 

 perfectly clean and free from marine deposit, with the exception of a slight film ; the thermo- 

 meter being at 215, and not having varied in excess throughout the voyage. This circum- 

 stance was without precedent ; no mud-plate having been removed, or men employed in the 

 boilers during the voyage. 



From extensive experiments of Dr. Davy, (brother to Sir Humphrey,) to ascertain the 

 relative saltness of the sea in various situations, its specific gravity was found to vary very 

 little, except when influenced by the influx of large rivers ; and this conclusion is corro- 

 borated by other scientific men, with whom I have conversed on the subject, in the 

 Mediterranean. 



From the coincidence of the above experiments, therefore, it may be inferred that the 

 water of the Mediterranean is not, in its effect, salter than that of the Bay of Biscay or the 

 Channel, that boilers hitherto incrusted must have contained a solution saturated to a much 

 higher degree than that exhibited in the case alluded to, and that marine boilers are not 

 more subject to incrustation during a voyage to the Mediterranean, than on any other voyage 

 of similar duration. Also from recent examinations of boilers returned from the West Indies, 

 and the reports from the ' Atalanta ' and ' Berenice ' steam ships sent out by the East India 

 Company, I am led to the same conclusion as regards the waters of the Tropics. 



t>. The specific gravity of the water of the boilers, as indicated by the thermometer 

 remaining uniformly at 215, and its not having indicated a higher degree of concentration on 

 either passage, the delay of blowing completely out on the voyage became unnecessary, and 



