SALTS OF LEAD. 593 



by dissolving litharge, at the boiling point, in slightly diluted 

 nitric acid, which should be free from hydrochloric and sulphu- 

 ric acids. The neutral nitrate crystallizes in large octohedrons, 

 with the secondary faces of the cube, which are sometimes trans- 

 parent, although generally white and opaque. The crystals are 

 anhydrous ; they are soluble in 7 1 times their weight of cold, 

 and in much less hot water. The nitrate of lead is decomposed 

 by an incipient red heat, yielding, with oxygen gas, the peroxide 

 of nitrogen, which is prepared in this way, and leaving the yel- 

 low oxide of lead. When a small quantity of ammonia is added 

 to nitrate of lead, or when a dilute solution of the neutral salt 

 is boiled with oxide of lead in fine powder, a soluble bibasic 

 nitrate of lead is formed PbO, NO 5 + PbO. It crystallizes 

 during evaporation in fine scales, or in little opaque grains, 

 which are anhydrous. The granular crystals decrepitate when 

 heated, with extraordinary force. The tribasic nitrate of lead 

 precipitates, when ammonia is added in very slight excess to a 

 solution of nitrate of lead. Its constituents are 2NO 5 , 6PbO 

 and 3 HO (Berzelius). It is a white powder, which is soluble to 

 a small extent in pure water. When nitrate of lead is digested 

 with a considerable excess of ammonia, the decomposition stops 

 at the point at which 6 eq. of oxide of lead are combined with 

 ] eq. of nitric acid. The sexbasic nitrate of lead contains 

 2NO 5 , 12PbOand3HO. (Berzelius). 



Nitrites of lead. When a solution of 100 parts of nitrate 

 of lead is boiled with 78 parts of metallic lead in thin turnings, 

 the lead is dissolved, and a little nitric oxide is evolved, the 

 last being the result of a partial decomposition of nitrous acid 

 previously formed. The solution is alkaline and yellow ; and 

 gives, on cooling, brilliant crystalline plates of a golden yellow 

 colour, which are the bibasic nitrite of lead, 2PbO + NO 3 . By 

 dissolving 100 parts of this salt in water at 16'7 (75 cent.), and 

 then mixing with the solution 35 parts of oil of vitriol, pre- 

 viously diluted with four times its weight of water, one half of 

 the oxide of lead is precipitated as sulphate of lead, and a solu- 

 tion is obtained of a deep yellow colour, from which the neutral 

 nitrite of lead, PbO, NO 3 + HO ? crystallizes. This salt gives 

 yellow crystals, resembling the nitrate in form. Its solution 

 absorbs oxygen from the air, and like all the nitrites, gives off 

 nitric oxide at 176 (80 cent.), and a subnitrate of lead precipi- 

 tates. Berzelius, to whom we are indebted for the preceding 



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