UPON THE SULPHATE OF LEAD. 
269 
neutral tartrate of ammonia. A concentrated solution forms 
after some time a stiff jelly, like silica." This last is no 
doubt a double tartrate of lead and ammonia. 
I had also observed, some time previously, that a solution 
of the citrate of ammonia, when poured upon the sulphate 
of lead and allowed to stand, altered the character of the 
sulphate, and this, with the other fact above stated, led to 
the examination of what was really the action of these as 
well as other ammoniacal salts in general, upon the sul- 
phate in question, and it is found that in every case it was 
decomposed. 
Citrate of Ammonia. — If a solution of citrate of ammo- 
nia be poured upon the sulphate of lead and shaken toge- 
ther, the clear solution will be found to contain the sulphate 
of lead, as shown by hydrosulphuric acid and a salt of ba- 
ryta — (taking care in testing with the baryta to acidulate 
first with pure nitric acid, to prevent the formation of the 
citrate of baryta.) If they be allowed to remain several 
weeks in contact, the solution will be found to contain more 
lead, the sulphate having undergone decomposition, sul- 
phate of ammonia and a double citrate being the result; as 
this latter salt is not very soluble, a large portion of it re- 
mains in the form of a precipitate. The rapidity of this 
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 per- 
fectly transparent ; 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, sul- 
phuric 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 
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