194 



Mb. J. Napiee on Incrustations in Steam BoUers. 



composed of magnesia ; but when magnesia had existed in the water, I 

 have never found a crust free of that earth. The crust or cake upon 

 fresh water boilers have generally more of a mixed composition than 

 from marine boilers. I wiU add a few of these as illustration. 



Carbonate from Fresh Water. 



Carbonate of lime, 

 Sulphate of lime, 

 Peroxide of iron, 

 Magnesia, 



79-0 

 6-3 

 3-5 

 21 



Silica, 



Water, at 212°, 



6-5 

 40 



100-4 



Another, from using water having sulphates in excess or carbonates — 



Sulphate of lime, . . 58'4 



Carbonate of lime, . 27 "3 



Carbonate of magnesia, . 6'2 



Peroxide iron and alumina, 3 '2 



Silica, 



Carbonaceous matters. 



2-0 



. 4-0 



100-1 



From a marine boiler, upon the iron plate, where care was taken in 

 blowing off regularly, runnmg between Aberdeen and Loudon. This is a 

 very hard, tenacious crust — 



Sulphate of lime, . . 79-2 Water, 



— magnesia, . 6-8 



Peroxide iron and alumina, 4-8 



. 6-0 



Chlorine and common salt, 2-4 

 100-0 



The next is from boiler tubes running between Glasgow and Liver- 

 pool. In this little or no care had been taken by the engineer to pre- 

 vent formation of crusts, which are composed of two distinct layers — the 

 one next the tube a pure crystalline cake ; that upon it was soft and 

 granular. The two measured from ^ to f of an inch thick. These two 

 layers separately gave — 



99- 



100-0 



The next is from the same boiler tubes, working the same length of 

 time, but every precaution and care taken by engineer. The crust was 

 only §• inch thick, and crystalline. 



