210 Mr. H. Medlock on the Action of Water upon Lead. 
resulting from the decomposition of nitrogenous organic matter 
will go on attacking and dissolving lead ad infinitum. Fach 
atom of nitrous acid, in acting upon lead, forms an atom of neu- 
tral nitrite of lead. Three atoms of this neutral nitrite, accord- 
ing to the above equation, attacks the lead vigorously, and forms 
the polybasic salt with simultaneous production of ammonia*. 
This ammonia is in turn converted by the action of the lead into 
nitrous acid, which in its turn attacks and dissolves its quota of 
lead. Thus, although the quantity of nitrogenous organic mat- 
ter in water may be very small, and the nitrous acid directly 
resulting from the oxidation of ammonia may be in very minute 
quantity, yet it will be evident from the foregoing remarks that 
the quantity will rapidly increase from a process of self-manu- 
facture which is continually gomg on. The nitrous acid, in 
attacking the lead, produces ammonia: this ammonia in turn 
becomes transformed into nitrous acid by simple oxidation. 
When nitrates are present in water, a similar action on lead is 
effected. The nitrate of lead produced in contact with the metal 
is speedily transformed into the quadribasic nitrite with evolu- 
tion of binoxide of nitrogen, which, by combining with another 
atom of oxygen, forms again nitrous acid. The formation of 
quadribasic nitrite of lead, from the nitrate in contact with me- 
tallic lead, is represented by the followimg equation :— 
5(PbO, NO®*) +11Pb=4(4PbO, NO) + NO?. 
The foregoing observations sufficiently explain why leaden 
pipes and cisterns are so rapidly destroyed by the action of cer- 
tain waters, while they are not acted upon by others. The chief 
conclusions arrived at from these investigations are,— 
Ist. That the action of water upon lead is entirely due to the 
presence of nitrous and nitric acids, resulting primarily from the 
decomposition of organic matters and of ammonia contained in 
the water. 
2ndly. That waters deprived of these acids, and of substances 
capable of producing them, have no action on lead, and may be 
conveyed with perfect safety through leaden pipes or stored im 
leaden cisterns. 
drdly. That carbonic acid exercises a de useful influence in 
decomposing the basic nitrite of lead formed, and precipitating 
the basic atoms of oxide as carbonate, leaving only very minute 
quantities of the neutral nitrite in solution. 
* Schonbein (Phil. Mag. vol. xii. p. 457) has shown that platinum and 
finely divided copper have the power of converting ammonia instantane- 
ously into nitrous acid. Most other metals, especially those which have a 
powerful affinity for oxygen, possess the same property. 
