270 
ACTION OF SOME OF THE ALKALINE SALTS 
possessing certain characters which do not belong to the 
simple citrate, I consider it a double of lead and ammonia. 
It contains not the slightest trace of sulphuric acid. It was 
not analysed, 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 sul- 
phate 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 few weeks, the pre- 
cipitate 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 completely soluble in 
dilute nitric acid, affording no precipitate with a salt of ba- 
ryta. If the mixture of the tartrate and sulphate be boiled, 
this change takes place more rapidly, and in a manner some- 
what 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 ebulli- 
tion, 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 tar- 
taric acid. This is different from what takes place with the 
citrate, which, when boiled 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, de- 
compose it in part, and form a double tartrate of lead and 
ammonia, which last salt is subsequently decomposed by 
continued contact with water, or still more rapidly by its 
solution being boiled. 
