531 



Of these coals the Sweet Vein was perfectly free from 

 sulphur ; the Rushes coal contained but a minute trace ; 

 but the Pollough coul contained a good deal, and as the 

 sulphurous acid produced during its combustion should be 

 absorbed by the potash, and counted as carbonic acid in the 

 analysis, it was necessary to correct the above result by a 

 direct determination of the sulphur. For this purpose 3.526 

 grammes of the coal were boiled with aqua regia, and the 

 liquor precipitated by chloride of barium. The sulphate of 

 barytes obtained weighed 1 .589 grammes, corresponding to 

 45.07 per cent., containing 6.18 of sulphur. 



Now, 6.18 sulphur give 12.36 sulphurous acid, and sub- 

 tracting that from the carbonic acid obtained in the elemen- 

 tary analysis, then converting the sulphur into bisulphu- 

 ret of iron, and subtracting the pyrites from the ash, 

 there comes out, as the true composition of the Pollough 

 coal: 



Ash, free from iron 

 Bi-sulphuret of iron 

 Carbon .... 

 Hydrogen . . . 

 Oxygen .... 



2.19 

 11.58 

 75 42*1 



"^•^^ C thracite 86.23. 

 8.40 



J 



100.00 



It is interesting to contrast the composition of the really 

 organic part of these three varieties of coal. 



Rushes. Pollough. Sweet Vein. 

 Carbon .... 93.53 87.46 94.39 

 Hydrogen . . . 3.63 2.79 4.05 



Oxygen . . . 2.84 9.75 1.56 



100.00 100.00 100.00 



By the practical mode of analysis these coals were found 

 to give, per cent. : 



