'^18 Ohen'alio7is respecting 



The following circumstance is particularly deserving of notice* 

 A part of the north wall of the laboratory, on which saltpetre 

 usually cfiloresced, having been covered with wainscot some 

 months since, and the wainscot having been painted with com- 

 mon white paint, 1 was surprised after a time in observing an 

 efflorescence on particular parts of the paint, similar to what 

 might have been expeete«l on the wall itself. Where this ef- 

 floreseence had taken place the paint was loosened from the 

 wainscot, and might be readily peeled off in small flakes. The 

 .saline particles of which this eHloresceuce consisted I at first 

 supposed to be nitrate <jf leail ; but upon examination in various 

 ways no trace of lead could be found in them, and they exhi-i 

 bited the principal characters of conunon nitre : they deflagrated, 

 lor instance, with charcoal, leaving a deliquescent alkaline re- 

 siduum. Many weeks have elapsed since that saline efflores- 

 cence was brushed off, but I have not vet observed any renewal 

 of it. 



Though the production of saltpetre had been pointed out to 

 me in the laboratory of the Ashmole Museum as long since as 

 the year 1S02, I was prevented by manv circumstances from ob- 

 serving with any degree of regularity or precision the phieno- 

 mena of this natural process previously to the connnenccment 

 of last year; about which time having carefullv brushed away 

 the whole of- tlie saline efflorescence from a part of the north 

 wall situated I)elow the level of the street, and very imperfectly 

 exjjosed to the liglit, I was surprised by the fact of its (luick re- 

 appearance. It was brushed away at the end of January ; but 

 within three days it had again effloresced in sufficient (luantitv 

 to present that appearance of hoar frost, or down, or mould, 

 ^vhich is very characteristic of the manner in which naturally 

 formed saltpetre is ofi;en accumulated ; and which a person, 

 utterly incapable of judging of the real nature of the substance, 

 described at the time by the term " damp." 



I was still more surprised, however, in observing after a few 

 days, that the quantity of tiie saltpetre was apparently very much 

 diminislied; and that at the end of eight or ten davs there was 

 scarcely any appearance of it remaining: though there was no 

 reason to suppose a particle had either accidentally fallen to the 

 ground or been intentionally removed. 



The same part of the wall was again brushed perfectly clean, 

 and I continued to make daily observations in expectation of a 

 renewal of the process ; but no new collection was perceptible, 

 excepting in the form of a very few detached and minute capil- 

 lary crystals, till the IGth of March; on which day, having been 

 absent dirisig the whole of the 1 4th and 15th, I found a more 

 abundant accumulation than in the preceding instances. 



