83 Action of some Alkaline Salts upon /Sulphate of Lead. 



solution become perfectly transparent ; if it be set aside and al- 

 lowed to cool, in the course of a few hours an abundant white 

 precipitate will be formed, and upon testing the clear solution, 

 sulphuric acid, ammonia, citric acid and oxide of lead will be 

 found present. The precipitate, when washed, affords citrate of 

 lead and ammonia. I was at first inclined to think it simply a 

 citrate of lead, attributing the ammonia present to some of the 

 citrate not washed out ; but from its possessing certain characters 

 which do not belong to the simple citrate, I consider it a double 

 citrate of lead and ammonia. It contains not the slightest trace 

 of sulphuric acid. It was not analyzed, from the difficulty of 

 obtaining it perfectly pure, as the water used to wash it decom- 

 poses it, and as yet this difficulty has not been surmounted. So 

 then the result of the action of the citrate of ammonia upon the 

 sulphate of lead is, first to dissolve it, and subsequently to de- 

 compose it, forming the sulphate of ammonia and citrate of lead 

 and ammonia. 



Tartrate of ammonia. — If a solution of this salt be added to 

 the sulphate of lead and shaken with it in the cold, the clear 

 solution will be found to contain both lead and sulphuric acid ; 

 and if set aside for a few weeks the precipitate will have changed 

 its character, having assumed a crystalline nature ; the solution 

 will no longer contain lead, but the quantity of sulphuric acid 

 present will be found to have increased. The precipitate now 

 consists of tartrate instead of sulphate of lead, which is com- 

 pletely soluble in dilute nitric acid, affording no precipitate with 

 a salt of baryta. If the mixture of the tartrate and sulphate be 

 boiled, this change takes place more rapidly, and in a manner 

 somewhat different from the case of the citrate ; the sulphate 

 will not be dissolved in such large quantities, and moreover by 

 continuing to boil the solution after the sulphate has been com- 

 pletely dissolved, the tartrate forms during the ebullition, and is 

 precipitated in little shining crystals. If the ebullition be con- 

 tinued a sufficient length of time, the whole of the lead previ- 

 ously dissolved will combine with the tartaric acid. This is dif- 

 ferent from what takes place with the citrate, which when boil- 

 ed upon the lead salt dissolves it, and no length of ebullition 

 will produce a precipitate. The action of the tartrate is first to 

 dissolve the sulphate, decompose it in part, and form a double 

 tartrate of lead and ammonia, which last salt is subsequently de- 



