6 JOURNAL OF THE 
ties is that noted in the action of the sulphate or alum, 
before and after heating, upon solutions of barium or lead 
salts. This was first observed by Loewel' and was 
studied by Favre and Valson.* A _ violet solution on be- 
ing treated in the cold with a solution of barium chloride, 
yields practically all of its sulphuric acid as barium sul- 
phate. A cold green solution forms a precipitate slowly, 
and even after a number of hours the precipitation is far 
from complete. On boiling, all of the sulphuric acid will 
be precipitated. Favre and Valson found that only one- 
third of the sulphuric acid present in the original chromic 
sulphate was precipitated in the cold by the barium 
chloride. 
Our own experiments upon this point were as follows: 
A weighed amount of the pure alum was dissolved and 
the solution made up to a definite quantity. Two aliquot 
portions were taken, one of which was heated for half an 
hour and allowed to cool. ‘Then both portions were pre- 
cipitated with an excess of barium chloride. It was 
found impossible to filter these immediately with asbestos 
felts or the best filter-paper. They were therefore al- 
lowed to stand about twenty-four hours. This very long 
standing probably changed the conditions somewhat, but 
we were unable to avoid it. Still the results would con- 
firm the observations of Favre and Valson. The pro- 
longed standing also showed that it was not merely a de- 
layed precipitation, but one partially prevented. 
I EH, 
Percentage of SOg3 in alum is 32.06............ 
Percentage of SOg in alum, violet solution 
PLECIMI ATEN GONE ok g by be a cee ew nS} yeaa le8 30.44 30.19 
Percentage of SO3 in alum, green solution 
heated one-half hour......... TREE OSE I 
Percentage of SO 3 in alum, green solution 
heated one hour: : oS. u ceo beet ree eR 22.87 21.83 
1J, Pharm. (3), 4, 32. 
2 Compt. rend., 77, 803. 
