ELISHA MITCHELL SCIENTIFIC SOCIETY. 7 
These experiments were upon solutions containing one 
gram to 100 cc. A solution twice as strong was next 
taken: 
i. Tk 
Percentage in violet solution precipitated 
COLES SSRN ES NORE Og en Sa eR teen 28.88 31.80 
Percentage in green solution (heated one 
nour) precipitated colds ys 2.3 5....5 0440. 19.55 21.47 
Again a solution containing 0.5 gram to the 100 ce. 
was taken. 
Percentage in violet solution precipitated cold....... 28.30 
Percentage in green solution (heated one hour) pre- 
SAWS eae GRC s 65'S sg ahi ey ofa ROG AIa 6 Ele aS ao. eS 23.00 
The difficulties of washing and filtering barium sul- 
phate precipitated in this manner account in part for the 
lack of agreement between the analyses, but two things 
are evident; first, that all the sulphuric acid is not pre- 
cipitated from either v olet or green solutiens in the cold, 
and, secondly, that a short boiling effects such a change 
that only two-thirds of the sulphuric acid is precipitated 
by barium chloride in the cold. he amount not precipi- 
tated ranged from 9.06 to 13.51 per cent. 
Many observations have been recorded as to the acidity 
of the violet and green solutiens of the alum. NRecoura! 
has stated that the vapors coming from a solution at 100° 
are acid, while the solid salt at the same temperature does 
not lose any acid. He further maintains that the green 
solution, left after the heating, contains a considerable 
amount of free acid. He made use of the heat of neutral- 
ization as a means of measuring the degree of acidity. 
A known amount of soda was added to the liquid and the 
heat liberated was measured. In so far as this corres- 
ponds with the heat liberated by the neutralization of free 
sulphuric acid in the same degree of dilution, he conclud- 
ed that he was dealing with free acid. According to his 
1 Compt. rend., 112, 1440. 
2 Ann. Phys. Chem. (3) 61, 218. 
