REPORT ON SOLUBLE CITRATE OF MAGNESIA. 
115 
would require the employment of 201 parts of citric acid to 60 of 
magnesia. The citric acid employed by Dorvault must be that 
expressed by the formula, (C l2 H 5 tJ 3HO) 2HO, which is ob- 
tained by precipitation from a hot solution, and which it is believed 
is rarely met with in our shops. Moreover, we must not overlook the 
fact that the best calcined magnesia of commerce is always more or 
less hydrated, and contains traces of carbonic acid. That used in 
preparing the accompanying specimens, a fair commercial article, 
was carefully examined. It effervesced on the addition of acid, 
and 50 grains thoroughly calcined in a platina crucible over a 
counter blow pipe, and weighed immediately, lost 4*5 grains, 
equal to 9 per cent. 
From these discrepancies, both in regard to the acid and base, 
we are led to suggest the following proportions, as more nearly 
representing the actual equivalents. 
Take of Citric Acid Crystallized, 100 grains. 
Calcined Magnesia, 35 " 
Water, 15 drops. 
Proceed as in the other case. 
By the use of these proportions, the 5 additional drops of water 
being rendered necessary from the fact of the citric acid containing 
only one equivalent of water of crystallization instead of 2, we 
should very readily prepare the neutral and soluble citrate, but for a 
practical difficulty arising out of the great comparative bulk of 
the magnesia, and the very small quantity of the liquid to absorb 
and combine with it. A portion of magnesia is almost unavoid- 
ably left uncombined, hence the acidity of the salt, and being 
mechanically mixed with the salt, it remains suspended when 
thrown into water, and gives it the appearance of partial insolu- 
bility. To obviate this last difficulty, the mass, when first taken 
from the capsule, and while passing into the brittle and pulverulent 
condition, should be dusted of all the adhering magnesia before 
being powdered. The heavy and very fine magnesia of C. Ellis 
& Co. was tried, but the combination was Jess complete than with 
the light magnesia of commerce. The action was so immediate 
and violent, that a portion of the magnesia was enveloped in the 
pasty mass without coming fully into contact with the fused acid, 
thus producing a very acid salt mixed with uncombined magnesia. 
