226 ACTION OF SOME OF THE ALKALINE SALTS. 



change is in proportion to the concentration of the solution 

 of the citrate. If instead of performing the experiment in the 

 cold we boil a tolerably concentrated solution of the citrate 

 with the sulphate of lead, a very large quantity of the latter 

 will be dissolved, and the solution become perfectly transpa- 

 rent; if it be set aside and allowed 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 decomposes 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 decompose 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 sul- 

 phate 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 completely dissolved, the tartrate forms during the 

 ebullition and is precipitated in little shining crystals. If the 

 ebullition be continued a sufficient length of time, the whole 

 of the lead previously dissolved will combine with the tartaric 



