OF ARTS AND SCIENCES. 



83 



Table XXI. 



" The mode of action of the saltpetre has been the subject of experi- 

 rhent. I had previously exposed bright bars of lead to natural waters 

 containing traces of nitrates, which were deprived of air and sealed in 

 glass flasks. Months had produced no action upon the lead, and had 

 conducted to the opinion, that lead was not acted upon by nitrates in 

 natural waters. As the reaction of the Cochituate or Fairmount water 

 was perfectly neutral, the decomposition of the saltpetre by free acid, 

 which should expose the lead to uncombined nitric acid, was not possi- 

 ble. Fresenius had observed that the carbonate of lead was less soluble 

 in water containing nitrate of ammonia and ammonia than in pure wa- 

 ter. I was aware that alkaline chlorides promoted the solution of cer- 

 tain lead compounds, and it occurred to me that they might 'be more 

 soluble in waters from the presence of nitrate of potassa, soda, or 

 lime. 



" In changing the waters, from day to day, exposure to the air would 

 furnish the oxygen and carbonic acid more directly than the absorption 

 from the surface, for the formation of the hydrated oxide and carbon- 

 ate, and these might to a slight extent, it seemed possible, experience 



confirmed it in the water of a great number of wells in Lowell." Appendix to 

 Tanquerel, p. 367. — Guy ton Morveau, most of whose labors belong to the last cen- 

 tury, mentions saltpetre as one of the salts denominated by him protecting in its in- 

 fluence on leaden pipes, when seeking to find the value as protectors of the differ- 

 ent salts occurring in natural waters. Christison. — Dr. Dana has ascribed a 

 prominent place to nitrates and chlorides in the action of well-waters upon lead. 

 Appendix to Tanquerel. — Experiments with graduated solutions of common salt 

 were made. See p. 74. 



