290 PHENOMENA OF DEW. 



The fait was not Upon an examination both of the water and the clay, with 

 cbTof the* 6 wn i c h the bricks were made, there are but faint indications of 

 bricks. the exiftence of this fait, at the fame time that the prefence of 



the muriatic acid is very perceptible. Is it poffible that the 

 muriatic acid may have been diflipated during the burning of 

 the bricks, and the fulphuric generated by the union of oxigen 

 Conjecture. with fome fulphureous matter exiiting in the coals ? I fear this 

 conjecture will be thought extravagant, but at prefent I fee 

 none which is more probable. 

 This Incident It is neceflary to add, that no injury to the plaifter appears 



the plaifter. to have arifen from the prefence of this fulphate of magnefia. 



XIII. 



Abftmft of a Memoir on the Dew. By Cir. Benedict 



PREVOST *. 



Well known J[-p j s known that a glafs veflel is fometimes covered with 

 tells more plen- dew in the midft of a veflel of lilver, which at the fame time 

 tifully,orinpre- remains dry ; and that mercury in a china veflel is not low- 



wd no^oTme- 5 ered b >' the devv ' thou S h the ed S es of the veflbl are ver 3 r Wet ; 

 t»ls. and it is very generally concluded from various experiments 



of this kind, that glafs is a fubftance upon which the dew is 



moll: plentifully depofited, while it is not at all precipitated 



on metals. 



Repetition of Cit. Prevoft was curious to repeat thefe experiments, which 



the experiments. ^ nQt p eem to ^ m to j ]ave j )een mac i e w j t h Efficient care, in 



order to determine to what degree of precifion it might be al- 

 lowable to fupport the ufual conclusion. In this repetition he 

 obferves fome very fingular facts, of which we fhall proceed 

 to give the general remits. 

 Difcs of metal l. Difcs of tinfoil, of gold, of filver, of copper, &c. being 



XnchangeT a PP lied <* ftuck to P lates of g lafs > and expofed to the dew, 

 with dew j tho* were often found to be no lefs charged with dew than the 



more frequently e l a fs itlelf on which they were placed; though it more com- 



they are dry and & J • , , , • , ., i r 



the glafs wet. monly happens that they remained dry, while .the glals was 



very wet. 



* Read to the Society of Sciences and Arts of the Department of 

 Lot, fitting at Montanban. Tranllated from the Annales de 

 Chiinic, XLIV. 75. 



2. la 



