I 



/ 



2IO 



MANURES. 



Sect. X. 5. 4. 



fly exifted both hi the calcareous earth of the felenite, and 



(hes of the gum arable 

 •Mr. Canton, in 



, in the Philof. Tranfad. Vol. LVIII. p. '^2>1'> P"^ 



lifhed his making a pyrophorus by calciniHg oyfter-lheils, and thei 

 mixino- them reduced to powder with fulphur, and recalcining then 



1 



clofe veffi 



This powder after being expofed to light, or heated 



by other means, became luminous in the dark for many min 



By 



this procefs the acid of phofphorus exifting in the animal (hell had 

 l>een decompofed by the red hot fulphur having robbed it of its oxy- 

 gen ; and thus the phofphorus remained un 



ted with th 



earth 



M. Du Fay, in a memoir publiflied in the year 1730, aflerts from 



periments, that all calcareous ft 



wh 



they 



ol 



acid or not, 



■with this difFeren 



pable of becoming luminous by calcui 

 ly, that the pure calcareous ftones req 



a 



I ' 



ftrontyer or repeated calcination ; whereas thofe, which contain an acid 



ypfu 



become phofphoric by fligl 



as felenites, or g 



M. Mart^raaf alfo aflerts, that all kinds of calcareous ftones may by 



be rendered phofph 



but thinks, that the p 



ones 



fhould be previoufly faturated with an acid. Keir's Did. Art. Phof- 



phoru 



And laftly, fome kinds of fluor, which is known to confift 



of calcareous earth and the fiuor-acid, emit phuiphoric light on be 



t> 



heated flowly, but loofe it, wh 



m 



h 



\J 



d. (Kirwan's Mi 



logy.) This material might probably as well as gypfum become ufe 



ful in ag 



4. Thefe experiments, w 



h 



(hew th 



common calcareous 



ftones, which 



ly carbonic acid, were rendered phofph 



by calcination ; but that thofe which did contain a fixed acid, as gyp 

 fum, and fluor, were rendered phofphoric with lefs difficulty, acquain 



t 



firfl with perhaps one very important u 



fe of 



me 



agriculture. 



Secondly, with that alfo of gypfum, or alabafter, which has lately 



been ufed in America and in Germany without previous calcination ; 



but 





