Mr. Hennell on the mutual action &c. 241 
for such decompositions by Dr. Prout and Mr. Cooper, 
Trans. Soc. Arts XLI. p. 56. In these experiments I always 
obtained, along with the other products, a considerable pro- 
portion of sulphurous acid, and afterwards upon washing the 
contents of the tube with water upon a filter, it was of a 
bluish tint, and held sulphate of copper in solution ; a result 
which I could not readily account for, as every precaution 
had been taken to free the oil of wine which I used from, all 
adhering sulphurous and sulphuric acid. 
I now added a few drops of the same oil of wine to a 
solution of muriate of baryta and gently heated the mixture, 
when not the slightest cloudiness was produced, although 
litmus paper indicated the existence of a free acid ; but upon 
evaporating the mixture a precipitate fell, when it became 
concentrated, and on boiling it to dryness, a considerable 
quantity of sulphate of baryta was found in the residue; it 
became evident therefore that the sulphuric acid was in some 
state of combination which prevented its usual action upon 
tests, or that its elements were in some peculiar state of 
arrangement in the oil of wine. 
To determine the quantity of sulphuric acid thus elicited, 
I boiled 200 grains of very carefully prepared oil of wine, 
free from all trace of acid, with a solution of caustic potassa 
to dryness ; the residue was heated red hot and dissolved in 
water, the excess of potash being slightly supersaturated 
with dilute nitric acid ; muriate of baryta was then added as 
long as it formed a precipitate, and 218,3 grains of sulphate 
of baryta were thus obtained. A repetition of this experi- 
ment gave the same results ; so that we may conclude upon 
the presence of 74 grains of sulphuric acid in 200 of oil of wine. 
