Mr. J. Napier on Incrustations in Steam Boilers. 197 



ascribed to that cause. I will not take up your time discussing the 

 theoretical views how crusts of lime or gypsum lining the inside of a 

 boiler must affect the transmission of the heat, but in respect to such 

 crusts affecting a boiler, hastening its destruction, and causing danger, 

 I refer to the recent report of the Society for the Prevention of Boiler 

 Explosions, in which it is shown that incrustation affects the boiler. 

 The report goes on to say — 



" And lastly, I may mention among the causes of fracture, the forma- 

 tion of a scale or certain kinds of deposits, which, by retarding the 

 transmission of heat, also allow the plates to become overheated. The 

 nature of these deposits, so far as regards their powers of conducting 

 heat, appears to vary greatly ; for while some boilers, although thickly 

 covered with scale, continue uninjured for years, others of similar con- 

 struction, and under like conditions, with only a shght deposit, but of a 

 different kind, require frequent repairs. On this subject there is, 

 evidently, need of further investigation. For the prevention and removal 

 of such deposits, various compositions have been employed with more 

 or less success ; but in the use of any composition it is preferable to 

 effect precipitation in a tank or reservoir previous to the water entering 

 the boiler. The employment of sediment collectors and frequent blowing 

 off is beneficial, and should not be neglected." 



Few things could show more fully the necessity of such associations 

 than this part of the report ; and we trust that the next report will not 

 contain a statement that certain deposits, though very thick, will do no 

 harm, while other certain deposits, though very thin, will destroy a 

 boiler, but will be able to say what these certain deposits are, whether 

 belonging to the sulphates or carbonates. 



I have lately had my attention drawn to the whole subject as a 

 matter requiring a little investigation, and have got a few samples of 

 crusts to analyze, some of which I have given. Where the crust was 

 carbonate I have found little difficulty in preventing its formation — 

 only a little care on the part of the engineer. As we have seen, this 

 falls as a precipitate by the mere boiHng of the water. If, every night 

 after the fire is damped down, and a little time allowed for this precipi- 

 tate to subside, it be then blown off from the bottom, little or no incrus- 

 tation will ever form upon the boiler. Such crust as the sample shown 

 is always seen in nightly layers, the result of a deposit upon the boiler, 

 which hardens and cakes by standing, and could all be removed by 

 mechanical means and attention. And I liave been told by engineers 

 who liave adopted this system of blowing off, that they do not require 

 to clean their boilers over once a-year ; while other parties, using the 

 same water, require to clean and chip off the crust every three months, 



