CHEMICAL PHENOMENA OF DIGESTION. % 141 
determined whether it exists in the gastric juice, or if under 
the circumstances of the operation it is not produced by the 
decomposition of a chloride. When you add to gastric 
juice, which as is known contains lime, a minimum pro- 
portion of oxalic acid, it is rendered turbid by the formation 
of an insoluble oxalate of lime, whilst a like quantity of the 
same reagent occasions no turbidness in water containing 
2000ths of hydrochloric acid, to which chloride of calcium 
has been added. 
This single experiment evidently shows that the hydro- 
chloric acid exists in the form of a chloride, and is not found 
in a free state in gastric juice. We shall have further oc- 
casion to confirm this fact by other experiments. 
Phosphoric acid being a fixed acid, we were required to 
seek it in the gastric juice, likewise concentrated by distil- 
lation ; the residue had acquired an extremely acid reaction, 
and effervesced with chalk, but never entirely lost its acid 
reaction, notwithstanding the excess of chalky carbonate. 
This property, joined to those given it by different authors, 
indicated in a positive maimer the presence of phosphoric 
acid in gastric juice. We afterwards saturated the juice 
with lime and oxide of zinc : the filtered liquors were neu- 
tral, and presented to us all the characters common to lime 
and zinc. This experiment proves that the phosphoric is 
not the only free acid of gastric juice, for had it been so, by 
reason of the insolubility of the two phosphates we should 
not have found either lime or zinc in the filtered liquid. 
We satisfied ourselves that such foreign principles as chlo- 
ride of sodium disguise nothing of the re-action. To de- 
termine now the nature of the acid, which, existing in gas- 
tric juice, could give rise to soluble salts of lime and zinc, 
we should bear in mind that it is an acid passing only with 
the last products of distillation, and does not precipitate 
salts of silver. 
Lactic acid exhibited to us similar characters ; we sub- 
mitted to distillation water acidulated with lactic acid, and 
vol. XI. — NO. II. 13 
