ALUMINA. 309 



4*504 grains of sulphuric acid ; if we add this to 

 the original loss, we obtain 48*124 grains for the 

 amount of the water and sulphuric acid in 

 60-875 grains of alum. Deducting the 20 grains 

 of sulphuric acid which we know to be present, 

 there remain 28*124 grains for the water of 

 crystallization. 



But an integrant particle of water weighs 

 1*125, and 1*125 x 25 = 28*125. From this it 

 is obvious, that 60*875 grains of alum contain 

 28*125 grains of water, which is equivalent to 

 25 atoms. 



3. 60*875 grains of alum crystals were ex- 

 posed in a platinum crucible to the heat of the 

 sand bath, and afterwards to a dull red heat for 

 an hour. Distilled water was poured upon the 

 residual matter in the crucible in successive por- 

 tions, and digested on it till it ceased to take up 

 any thing 5 this water being evaporated to dry- 

 ness, left 11 grains of sulphate of potash. Hence, 

 60*875 grains of alum contain 6 grains of pot- 

 ash. We see, too, that one-fourth of the sulphu- 

 ric acid is united to the potash : the remaining 

 three-fourths must be in combination with the 

 alumina. 



4. To obtain the alumina, 60*875 grains of 

 alum were dissolved in distilled water, and to 

 the solution was added the quantity of carbonate 

 of potash just necessary to saturate 15 grains of 



sulphuric acid. The experiment was repeated 



us 



