3813.] Azote, of Hydrogen, and of Ammonia. 361 



nitrate of lead with metallic lead in an apparatus proper to 

 collect the gas which might be evolved. The apparatus was 

 surrounded with hot water," into which I had put a thermometer. 

 When the water acquired the temperature of 131° the lead 

 began to tarnish, and at 140° it was covered with a white crust, 

 and the liquid began to acquire a yellow colour at 167°. There 

 was a sensible action between the lead and the liquor, but still 

 without any disengagement of gas. At 176° bubbles of air 

 slowlv formed, and the action was increased. 1 then diminished 

 the temperature to 167°, and I kept it nearly at that tempera- 

 ture for 36 hours. There had disengaged about -^th of a cubic 

 inch of gas, which was a mixture of nitrous gas and of azotic 

 gas driven from the solution by the elevation of the temperature. 

 The lead was entirely covered by a white crystalline crust ; and 

 a quantity of the same substance crystallized on the inside of the 

 glass during the cooling. The liquor had a fine yellow colour, 

 which it retained even when cold. On examining it, I found 

 that it contained a small quantity of nitrate of lead not decom- 

 posed, and neutral nitrite of lead, to which it owed its colour. 

 The white crystalline precipitate was the first submtrate. When 

 heated it lost".-! per cent, of water; and when raised to a red. 

 heat, 19 percent, of nitric acid were disengaged, leaving 78 

 parts of yellow oxide of lead. This experiment proves that the 

 nitrite may be formed without the disengagement ol nitrous gas; 

 and it is evident, that when nitrous acid is formed at the same 

 time that the base increases in quantity, it is the nitric acid that 

 ought in the first place to combine with that excess, because its 

 affinity for the oxide of lead is stronger than that of nitrous 

 acid. ' After this long but necessary digression, we wdl resume 

 our examination of the decomposition of nitrate of lead by lead 

 in the metallic state. 



We have said that when Az 6 + P O has dissolved an 



additional P, it is converted into Az 6 + 2 P O ; that is to 

 say, when !00 parts of nitrate of lead have dissolved 621 

 pans of had (a quantity equal to that previously contained mthe 

 nitrate), the whole is converted into nitrite : and when a greater 

 quantity of lead, as, for example, 7<) parts, is dissolved, a con- 

 siderable quantity of snbnitrite at a maximum must be formed, 

 at the expense of the nitrous acid of the nitrite; but 1 have 

 proved that LOO parts of nitrate of lead are capable ol dissolving 

 77 9 parts of lead before any perceptible trace of suhnitnte at 

 a maximum can be discovered (Ann. de Chim. July, 1M '-')j 



that I- to say, that the same Milmitiilc, which is already lonned 



when t liquor has dissolved 62j parts of had, continues still 

 to be formed till the liquor has dissolved /8 parts of lead. This 

 experiment proves, then, thai nitric acid has more oxygen to 

 Jose before it is converted into nitrous acid than is consistent 



