January 6, 1872.] THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
547 
CITRIC ACID AND A NEW CLASS OF 
COMPOUND CITRATES. * 
BY J. CREUSE. 
Having undertaken the study of the citrates as a class, 
•*and especially of those of the citrates where the acid is 
combined with more than one base, the first difficulty I 
met was how to estimate citric acid without having re¬ 
course to the long and complicated process of an organic 
elementary analysis. I consulted the most recent pub¬ 
lications and some eminent chemists without obtaining 
my desideratum, viz.—How to estimate citric acid free 
and combined, in the same direct manner as sulphuric or 
muriatic acid ? The only thing then left for me was to 
try mj^self and find such a process, in which I succeeded, 
after many failures, including an explosion of citrate of 
silver. 
Care must be taken in this case, as in the others, that 
the saturation be as perfect as possible, for an excess of 
acetic acid causes the citrate of baryta to become soluble 
in alcohol, and an excess of alkali would precipitate some 
free baryta. 
The solution of acetate of baryta used for these ana¬ 
lyses may be prepared by treating pure diluted acetic 
acid by an excess of carbonate of baryta, heating to 
ebullition, adding some alcohol when cold, and filtering. 
This solution may be filtered to contain 5 per cent, of 
baryta, so as to know very nearly how much of it is ne¬ 
cessary to precipitate the alkaline citrates thoroughly, 
without too much excess of the reagent. The addi¬ 
tion of alcohol ensures its keeping unchanged for an un¬ 
limited period. 
I need not describe here any analysis of citric acid, 
but I shall describe the analysis of some metallic citrates. 
This process is founded on the fact that while the al¬ 
kaline citrates, the alkaline acetates and the acetate of 
baryta are freely soluble in alcohol sp. gr. 0-805 (63° 
'Tralles), citrate of baryta is completely insoluble in that 
menstruum. 
As the presence of alkaline acetates does not interfere 
with the reaction, this enables the chemist to estimate 
•citric acid in almost any shape, for free citric acid may 
be saturated by an alkali, alkaline citrates may be ana¬ 
lysed directly, and other citrates may be converted into 
-citrate of potash without difficulty. This method present¬ 
ing peculiar features, I will describe it in full. 
If the citric acid to be estimated is in the shape of an 
alkaline citrate, take from 1 to 2 grams of the salt, 
dissolve in 10 to 20 c.c. of water, neutralize the solution 
with acetic acid if it is alkaline, with ammonia if acid ; 
add a slight excess of a neutral solution of acetate of baryta 
and twice the volume of the whole liquid of alcohol 95°. 
Allow it to rest from twelve to twenty-four hours; the 
citrate of baryta, which is at first like a thick jelly, has by 
that time become denser and easier to wash. Transfer the 
■whole to a filter; but as some of the precipitate always 
■adheres to the sides of the vessel, it is recovered thus: 
pour into the vessel 10 to 15 c.c. of water, turn it round 
so as to wet all the parts where any salt adheres: citrate 
■of baryta, being to a certain extent soluble in water, is 
•soon taken up; add then double the volume of alcohol and 
pour on the filter with the first product. This being re¬ 
peated a second time, all the citrate of baryta may be con¬ 
sidered as collected on the filter. Wash this thoroughly 
with alcohol 63° and dry at a moderate heat. The pre¬ 
cipitate thus obtained represents all the citric acid in the 
shape of the citrate of baryta; 3BaO,C 12 H 5 O u with a 
variable proportion of water. 33 ut this salt is too hygro- 
metric to give correct results if weighed directly; it is 
necessary to transform it into sulphate of baryta. This 
is done without difficulty by burning the filter and heating 
the ashes and precipitate to red heat with sulphuric acid 
several times till a constant weight is obtained. This 
being ascertained, the weight of the citric acid may be 
•calculated within 2 milligrams. 
If free citric acid is to be estimated, a convenient 
quantity may be first saturated with a titrated solution of 
caustic soda, which gives generally a little more than the 
actual strength; the citrate of soda may be then treated in 
the manner described above, which gives a result a little 
below the truth, and the average between the two will 
be within 1 milligram. 
If it is necessary to estimate the citric acid of a non- 
alkaline citrate, soluble or otherwise, the analysis is con¬ 
ducted in this manner: a certain weight of the salt, from 
§ grm. is heated carefully with a solution of caustic 
soda or potash in excess; the heat must be applied long 
enough to decompose the salt thoroughly, but not enough 
to alter the citric acid. The liquid is then filtered, the 
filter washed as usual, and the liquor, exactly saturated 
\with acetic acid, may be treated as an alkaline citrate. 
* Reprinted from the American Journal of Pharmacy. 
ANALYSIS OF CITRATE OF BISMUTH. 
This citrate of bismuth is the salt obtained by preci¬ 
pitating acid nitrate of bismuth by an alkaline neutral 
citrate. It is insoluble in water, and may be obtained 
pure without difficulty; 2 grams of this salt were taken 
and decomposed by an excess of caustic potash, at a mo¬ 
derate heat. The precipitate of teroxide of bismuth well 
washed and dried was found to weigh T122 grm. The 
washings were collected together, saturated with acetic 
acid, treated by acetate of baryta and alcohol, as already 
mentioned, and the citrate of baryta thus formed, yielded 
T674 of sulphate of baryta, which corresponds to 0’788 
of citric acid. The balance 0-09 represents the equiva¬ 
lents of water and the loss. Hence, we may figure the 
result thus :— 
Teroxide of Bismuth . T122\ 
Citric Acid (anhydrous) 0'788 
Water.0-086 
Loss.0-004 
or in 
other 
T 170 = 1 equiv. 
0-825 = 1 „ 
0-090 = 2 ,, 
terms | 
2-000 ) 
2*085 
From this we may deduct for citrate of bismuth the 
following formula:— 
Bi0 3 , C 12 H 5 O n + 2 HO = 417. 
ANALYSIS OF THE DOUBLE CITRATE OF BISMUTH AND 
AMMONIA. 
This salt is commonly called ammonio-citrate of bis¬ 
muth or soluble citrate of bismuth. It is obtained in 
two forms, in solution and in scales. In solution it may 
be either acid or neutral, in scales it is always acid on 
account of the loss of some ammonia during evaporation. 
It is very extensively used in medicine, but unfortunately 
is rather unstable in solution. 
The analysis of the neutral salt offered no difficulty : 
2-085 grm. of insoluble citrate of bismuth were weighed in 
a small porcelain dish, a little warm water added, and a 
small piece of litmus paper allowed to float on it. Then 
a filtered solution of ammonia containing 0-26 of am¬ 
monia to the 100 measures was cautiously added, the 
mixture being stirred all the time. As the last drop of 
the 100 measures fell into the porcelain dish, the litmus 
paper, red until then, turned blue, and in the same time 
the liquid became perfectly clear. 
This gives for the neutral citrate of bismuth and 
ammonia the following formula :— 
2NH 3 ,Bi0 3 . C 12 H 5 O n + «HO; 
The analysis of the salt in scales was conducted in this 
wise: 2-302 grms. of the ammonio-citrate of bismuth in 
scales were dissolved in a little warm water, and a small 
piece of blue litmus paper made to float on the liquid. 
The paper turned red immediately. Then the same fil¬ 
tered solution of ammonia already mentioned was added 
carefully till saturation; 25 measures were necessary, 
which corresponds to ^ equivalent. This demonstrated 
