OECT. V . 



/ 





'I 



•8 



of 



Jruall, 



n\ 





nic 



m 



. '"s oxv. 



IS curl 

 I 



Oufly I 



have feea 

 them have ob. 



'^'^s; butv.!"' 



' -A 



^ ^vhichpens. 



dtoth 



pen' 



e oim 



* 



e (lones, v, hicli 

 d clay, and hav- 

 : fome metaEic 



: pcrh:p3 from 

 I then (^nSd 

 been fuppo^^'' 



indurated ^^^^' 



remar 



e flu.'- 



,arei!fl' 



:ous 

 he 



ones 



combine 



; nation 



h -reater 



degf^^ 



h 



.^.raifeS^P''^ 



101 



Ivedth'/ 



dof 



ve 



ere 



tatio^ 



on 



\0^^ 





*^ 



Sect. X. 7.4. MANURES. 



When marl, which confifts of clay, calc 

 •which are frequently coloured red by 



22| 



eous earth, and fand, 

 blue probably by man- 



ft 



fe, is expofed in fmall lumps to the atmofphere ; it is liabl 

 mble into powder, which 1 fuppofe to arife from a fimilar circi 



that the oxygen of the atmafphere uniting with 



the metallic particles it poffeffes, lets at liberty the fame gas, or fteam., 

 which is feen to rife from clay, when thrown on heaps for the brick 



kiln or pottery ; v 

 •of lime are broke 



hich breaks the lumps into powder, as th 



mp 



h 



1 into powder by the fteam, w 

 thrown on them, by the heat fct 



D 



berty by the 



combination of the lime and wate 



This union of oxygen with the clay, or vwith the metallic part 



mino-led with it, I fuppofe to be much facilitated by expofin 



red heat, as 



burning brick 



while a greater h 



ay 



unite fo 



much 



xy 



with it as to turn it into glafs. Exadly fuch a pro 



cefs occurs in the produdion of minium 



quantity of h 



With the contaa of air combines fo much oxygen with the melted 

 d, as to form an oxyde ; a greater quantity of heat converts it into 



o-lafs 



4. When clay Is united with fo much oxygen by fire as to form \ 

 foft or imperfea brick, it polTefTes the power cf promoting the ge 



of the nitrous acid in certain fit 



fe 



like an efflorefcence on 



moulderine walls, having 



t) 



which is frequently 



become by 



the addition of lime 



The ufe of thefe foft brick 



I, 



:the produaion of nitre is well known in Paris, where the rubblfli of 

 old houfes Is regularly purchafed for that purpofe ; wh 



ch before 



t 



was a royal 



faa 



d mixed with th 



As thefe foft efflorefcent bricks from old houfes are known power 

 fully to promote vegetation, when pulverized ai 



at the fame time that they are capable of producing the nitrou 

 ; 1 imagine, that the ufe of paring and burning the turf of fom 



^11 

 ^cld 



ly enclofed commons depends on 



th 



mft 



Th 



IS 





that 



