tome 



ALUMINA. 



as united to the alumina ; so that the quantity 

 of silica actually united with the alumina, ac- 

 cording to Stromeyer's analysis, is 4-915. Now, 



24-915 : 28-669 : : 2 (atom of silica) : 2-3013 = atomic Gives 

 weight of alumina. 



3. HARMOTOME. 



This mineral, which occurs in a state of great 

 purity in the lead mine at Strontian, in Argyle- 

 shire, was found, by Klaproth, to be composed 

 of the following constituents : 



Silica . . 49 



Alumina . 16 



Barytes . . 18 



Water . . 15 



98 



Let us consider this mineral as a compound of 

 3 integrant particles of trisilicate of alumina, 

 and 1 integrant particle of bisilicate of barytes. 

 Then, 



(1.) 2-25 (atom of alumina) : 6 (three atoms silica) : : l6 



(alumina in the mineral) : 42-666 = silica united to 



alumina. 

 (2.) 9-75 (atom of barytes) : 4 (two atoms silica) : : 18 



(barytes in the mineral) : 7*384 = silica united to 



barytes. 



But 42-666 + 7-384 = 50-05 ; and this exceeds 

 the silica found in the mineral by 1-05 grain. 



T2 



