42 SOME NOTES ON ANCIENT MOETAES. 



near N'aples, is the product of volcanic eruptions, and has 

 this composition : — 



Per cent. 

 Silica 45-56 



Alumina 14-24 



Lime 8-94 



Magnesia 3-90 



Oxides of iron and titanium 11-02 



Alkalies and volcanic substances . . . .5-70 



Water 10-64 



However, it was not needful for the Romans to have 

 brought a pozzuolana from Italy, for they had already found 

 beds of trass near Bonn which have been worked ever since 

 they jfirst quarried them. Like pozzuolana it is of volcanic 

 origin, and has doubtless been thrown out of the burning 

 mountain of Eifel. The following is an analysis of a sample 

 of trass : — 



Per cent. 



Silica . . . . ' 10-92^ 



Oxide of iron 11-29 



Manganese trace 



Alumina , . . 18*52 y^ 



Lime 3-81 3 



Magnesia 2-54 -3 



Alkalies 3*01/ ^ 



Silica 38-12 



Alumina 0-92 



Oxide of iron 0-74 



Lime 2-81 [Iq 



Magnesia 0-19 ^ 



Alkalies 1-05 § 



Water, with traces of ammonia .... 9-09 



In conclusion, it is interesting to note that Mr. W. B. 

 Roberts ^ analysed some specimens of old mortar from the 

 walls of a building erected about 200 years ago, and he 



1 " Chemical News," vol. 400, p. 25. 



,^ 



N 



