.,^6 Experiments^ and Obfervations^ ':_ 



dtferetit fgeoies. - ; May we not thew conjefture^ that this change 

 |ii).l^e limeftope bs caufed by^ a epii^bination of the kmd I have 

 mentioned i,an.d the rather, as we hiid^>vhe.ak.is expofed only 

 to tj^ aQioii of -tlie -air^ and not, waflied by. water, that it forms 

 fy^jLoe qfflpreijrences, w):|ich fpeak tl^e ufliion of alkaline aqi^y.^nd 

 , earthy; fub,llances. Dr. Wai,/m',te\\^]TQiSy jthat, from the mortar 

 . ofan old [barn that was covered , with; thefe efflorefTences, he 

 .^ .graded perfed. jcryftals of pure nitre, without the application 

 ©f^any alkali; ^ndyet w£ knpw, that an alkali and an acid are 

 eflential-in di^,c^Ojinpoli,uon;Qf nitre.-— IJe. does not' attempt to 

 account for. thisr—^I fliouldhowv:erprefume, that it couJ,d only 

 happen by the lime in the mortar, having recovered a nitrous 

 acid from the air, inftead of the fixed air it had loft, and that 

 the putrid exhalations from the vegetables contained in the 

 barn, had furniftied the alkali, and that from the combination 

 of thefe, with the moifture of the air, relulted thofe effloreff- 

 ences that formed the nitre. Dr. Black ailerts, that the 

 effloreffences found in damp caverns or cellars in England, 

 contain a great proportion o{ fojjil alkali — this alkali is not 

 foiirid in Europe, unlefs combined with fea fait, of which it 

 makes the bafis ; and yet thefe eflloreffences are derived 

 from the moifture of die air : does not this argue the exiftence 

 of an alkaline fait in the atmofphere ? 



It maybe objeded, that if alkalies and acids exift in the 

 atmofphere, dicy would by dieir union form neutral lalts in 



