336 FACTITIOUS PUiZOLANA, 



fpe&ive proportions of the puzzolana and the lime, I could 

 always be alfared of the folidity of my cements. 

 "Exterior charac- There remains for me to dclcribe the exterior characters of 

 •addes uSw" 01 * lllC S uarlzi ^ r °u s ferruginous oxides, which form the bafis of 

 my factitious puzzolana, and to relate the analyfis of them 

 winch I made about 18 years ago. I will content myfelf with 

 offering the comparative ref'ults with the Italian puzzolana, 

 both in the dry way and the moid. 



Exterior Characters of the quartziferous Oxides of Iron. 



Their colour is of a reddifh-brown before calcination, or 

 Slight caki- Sightly violet. A light torrification gives them a clearer red tint 

 them from brown or a deep violet : one more intenfe renders them of a deep 

 to red. brown or of a violet-brown inclining to a black. The degree 



ch*m*^*em tc°^ llie c*tainati<Mi for ufe is coufmed to thofe two ftates. 

 z deep brown. Urged at a longer continued heat, the colour becomes a 



jJJSten ^ dee t ) black ' then the fubftance becomes porous, entirely fimi- 

 them black and Jar to certain lavas of our modern or ancient volcanos, with 

 porous like lava. uhich jj }s then fiffc^ no t to confound them. 

 Their fracture Their fracture is grained and a little earthy, and fmall cryf- 

 graiped and ta j s f q Uar(z mav ^ e diftingu iftied in them by the naked eye, 

 contain quartz and almoft always angular fragments of gray or milky quartz; 

 cryftals. a powerful magnifying lens caufes in feme fragments the dif- 



Needles of covery of needles of Ichorl, the amphibole of Hauy, and fome 

 fcborl, arnphf- f „ ; ourma!ines# 

 bole, and tour- 

 malines. Their fmell is ftrongly argillaceous on breathing on them 

 Their fmell ar- wilh the mouth, 

 gillaceous. 

 Give no fpaiks. There is no fire produced by the ufe of the fteel, when it 



does not firike a quartofe particle. 

 Do notefFer- They do not eftervefce with acids either cold or hot. 



v « efce "ir xx i'i The magnet ads a little on thefe oxides before calcination, 



Are affetted by to 



the magnet. and ftrongly, or perceptibly, after it. 



Weight of a The medium weight of a cubic foot, is 125° ; that of the 



cubic foot. Italian puzzolana is but 9 J °. 



Analyfis by the moifi Way. 



Analyfis in the I fiiall not weary the aflemb'y by a 'detail of the manipula- 

 moift way of the i\ ons relative to the folvents and re-agents which art ufes for 

 the decompofition of bodies, and fliall only fay, that filex, 

 iron, alumen, and a fmall portion of mangincfe, are the con- 

 stituent parts of thefe oxides. 



I repeated 



