Mh. J. Napiee on Incrustations in Steam Boilers. 195 



Water, .... 2-4 



Salt, &c., . . . 1-1 



100-0 



Sulphate of lime, . . 94-5 

 Magnesia, . . . 1'5 

 Peroxide of iron, . . '5 



This shows what may be done by care ; but I may mention that there 

 was a constant blow off from the boiler to an extent of three-fourths of 

 that boiled off as steam. So that this cake may be looked upon as 

 being only one-fourth of that which would have been formed without 

 blowing off. 



It will be seen from the specimens that the sulphate cake is crystal- 

 line. The water, by evaporation, becomes saturated with the salt when 

 it crystallizes ; and this saturation being kept up by the supply water, 

 these crystals grow up, not in an isolated form, but as a plate over the 

 whole surface of the boiler, and more on those surfaces exposed to fire ; 

 and the thickening of this plate is the extension of the crystals, which 

 stand upon their points or axes — that is, the crystals of the plate 

 arrange themselves in a line with the heat current, in the same manner 

 as fused solids crystallize under the influence of rapid cooling. 



I will now glance at a few of the remedies proposed to prevent incrus- 

 tation. The first is adding to the boiler a little muriatic acid. This 

 acid will act upon carbonate of lime, and produce a very soluble salt, 

 chloride of calcium, which will not form a cake ; but it has no action 

 upon sulphate of lime, which is the principal ingredient of boiler cake ; 

 and besides, this remedy must be used with the utmost caution, as any 

 excess of acid over the quantity required for the carbonate of lime will 

 act upon the boiler, and also pass off with the steam, and corrode joints 

 and stuffings. Indeed this remedy cannot be used with safety even 

 under the constant superintendence of a chemist. 



Another universal remedy was suggested by Eitterbrandt, namely, 

 Salammonia. This salt, put into a boiler with sulphate of lime, has no 

 action further than rendering the sulphate a little more soluble, making 

 it a little longer before crystallization begins ; but salammonia decom- 

 poses carbonate of lime, producing carbonate of ammonia and chloi'ide 

 of calcium, both soluble salts. Should there exist any sulphates in the 

 water, this reaction will be immediate, followed by another ; the carbo- 

 nate of ammonia will decompose the sulphate of lime, and form carbo- 

 nate of lime and sulphate of ammonia ; but the practical defect in this 

 case is, that whenever the carbonate of ammonia is formed it volatilizes 

 with the steam, and destroys the buskings, and everything containing 

 copper, and is hurtful to the tubes of tubular boilers, which are com- 

 posed of copper and zinc. 



Carbonate of soda has been tried, which decomposes the sulphate of 

 lime, producing sulphate of soda and carbonate of lime. As a precipitate 



