198 Mr. J. Napieh on Incrustations in Steam Boilers. 



at least. The sulphate crust, as already stated, is a crystallization upon 

 the surface of the boiler, and cannot be removed by mechanical means. 

 It is, however, easily and thoroughly decomposed by carbonated alkalies, 

 the cheapest is soda. It has been already stated that the only defect in 

 soda was its being added indiscriminately and in too large quantity — a 

 circumstance easily avoided. I make the matter a chemical question, 

 analyze the feed water to ascertain the amount of sulphate of lime which 

 is present in the gallon, take the size of the boiler and quantity of feed 

 water added per day. I then calculate the amount of carbonate of soda 

 that will exactly neutralize the sulphate of lime in the quantity of feed 

 water taken per day, which is dissolved in a small iron tank placed 

 above the boiler. If the engine works twelve hours, I form a syphon 

 that will run this soda liquor in the feed water in that time, so that at 

 no time is there an excess of soda in the boiler, and thus the lime is 

 converted into the state of carbonate, which precipitates, and may be 

 removed by mechanical means of judicious blowing off, as I have de- 

 scribed. I have only had the opportunity of trying this one boiler, 

 using the filthy water of the Kelvin. The blowing off was not carefuUy 

 attended to ; nevertheless, after six weeks, the usual time of cleansing 

 and scaling, which generally gave a crust of r», there was nothing but a 

 loose sludgy deposit, which was brushed off by a hard hair brush. 



In marine boilers using sea water, as already stated, the cake is always 

 the sulphate crystals, although where there is no mechanical care, car- 

 bonate crusts will also form. The use of soda in this way would be very 

 simple, and possibly, from their constant blowing off from the surface 

 this carbonate of lime might be, like the salt, carried to the surface, in 

 the first instance, and blown away while working, and would not cake 

 upon the tubes ; but its application and effects upon sea going vessels I 

 have had no means of testing. An analysis of sea water will not require 

 to be made for each vessel, as with land boilers, but an average analysis 

 may be taken. I say an average, because in different localities of the 

 sea, and even on different days, or probably seasons of the year, the sul- 

 phate of lime in sea water varies very much. However, this is a subject 

 I am not yet prepared to enter into. Instead of adding the precipitate to 

 the boiler, if mechanical means cannot throw off the precipitate entirely, 

 then a pair of tanks in which the precipitate may be made and the 

 boiler filled from the clear, would not be a very expensive nor unwieldy 

 piece of apparatus, which I do not consider, however, necessary, as me- 

 chanical means can be got for blowing off any accumulation of loose 

 precipitates. 



T have now done what I had intended in my own mind, nauiel}'', to 

 bring the subject before the Society, in hopes of drawing the attention 



