jB t)r. Wall on the Origin of the 



the fun feldorrs has adminion. It is built of ftonc, 

 and therefore, except when the fires are kept up 

 for the lectures, or occafional experiments, is 

 liable to be damp. The wall, to which I allude^ 

 is immediately under a retired pafiage, a very 

 convenient place of retreat to foot-paiTengers 

 under certain circumftances of necefTity. The 

 ground, therefore, and the adjacent wall have been 

 for years largely impregnated with excrementitious 

 animal fluids, in all the different ftages of putrcr 

 fadion. The faline tfflorefcence on fuch walls 

 is fometimes fuppofed to be alkaline, and really 

 to be the fofiile alkali ; but that in this inftance, 

 \vith which others of a fimilar fort probably have 

 fome analogy, it was perfed nitre, the following 

 remarks will evince. 



The fait deflagrates readily with charcoal, oi 

 fulphur, and leaves an alkali exadly fimilar in 

 tafte to that of the nitrum fixum. It does not 

 deflagrate per fe — It does not give out the fmcll 

 of hartfliorn, or the volatile alkali, when lix- 

 ivium tartarl is poured upon it either in a dif- 

 folved, or a dry ftate. A filtered folution of It 

 fuffers no precipitation, on the addition of lixiv, 

 tartari. A fmall quantity of this folution evapor- 

 ated to cryftallization (hoots into long, filamen- 

 tous, not cubical, cryflials, exactly the fame as 

 thofe obtained from an equal quantity of 

 folution of nitre, by the fame mode of treatmentj 

 ^nd indeed, the efflorefccnce on the v.'alls, where 



it 



