252 Dr Davy on the Incrustation 



means of flame kindled with oakum, after emptying the boiler and 

 drying it. Of all the methods hitherto used, that of" blowing off," 

 — that is, the discharging, by an inferior stop-cock, a certain quan- 

 tity of the concentrated water of the boiler by the pressure of steam, 

 after the admission above of an equivalent quantity of sea water of 

 ordinary density, appears to be, from the reports made, the most 

 easy in practice, the least unsuccessful, and the most to be relied on. 

 But, as in the instance given of the North American steamer, it can 

 be viewed only as a palliative. 



Considering the composition of the incrusting matter and the 

 properties of its principal ingredient — the sulphate of lime, a 

 compound soluble in water and in sea water, and deposited only 

 when the water containing it is concentrated to a certain de- 

 gree, there appears to be no difficulty theoretically in naming a 

 preventive. The certain preventive would be the substitution of 

 distilled or rain water in the boiler for sea water. Of this we have 

 proof in the efficacy of Hall's condenser, which returns the water 

 used as steam, condensed, after having been so used : — but, unfor- 

 tunately for its practical success, the apparatus is described as being 

 too complicated and expensive for common adoption. Further proof 

 is afforded in the fact, that the boilers of steamers navigating lakes 

 and rivers, in the waters of which there is little or no sulphate of 

 lime, month after month in continued use, remain free from incrus- 

 tation. This, I am assured, is the case with the steamers that have 

 been plying several summers successively on the lake of Windermere. 

 And it may be inferred, that, in sea-going steamers in which sea 

 water is used in the boiler, — or, indeed, any water containing sul- 

 phate of lime, the prevention of deposition may be effected with no 

 less certainty by keeping the water at that degree of dilution at which 

 the sulphate of lime is not separated from the water in which dis- 

 solved. From the few trials I have made, I may remark, that 

 sulphate of lime appears to be hardly less soluble, if at all less, in 

 water saturated with common salt than in perfectly fresh water. This 

 seems to be a fortunate circumstance in relation to the inquiry as to 

 the means of prevention, and likely to simplify the problem. 



If these principles be sound, their application under different cir- 

 cumstances, with knowledge and judgment on the part of the directing 

 engineer, will probably not be difficult. His great object will be in sea- 

 going steamers to economize the escape of water in the form of steam, 

 and thereby also economize heat and fuel ; — also, when fresh water is 

 available to use it as much as possible ; and further, to avoid using 

 sea water as much as possible near coasts, and in parts of seas where 

 sulphate of lime is most abundant. 



From the incrustation on the boilers of sea-going steamers, 

 the attention can hardly fail to be directed to that which often 

 forms, to their no small detriment, in the boilers of locomo- 

 tive-railway engines, and of engines employed in mines, and in 



