96 
the column of the liquid. In order to he perfectly sure of 
the purity of carbon dioxide gas, it was passed through a 
series of flasks containing distilled water, and then through 
a long tube containing solid sodium bicarbonate, to keep 
back any free acid which might be mechanically carried 
over. 
After passing a steady current of the gas through for 15 
minutes, the water in the cylinder was tested for acids 
other than carbonic. The absence of sulphuretted hydrogen 
was also proved by exposing a paper moistened with lead 
acetate solution. 
Then about *07 grams of ultramarine infused in 2 cc. of 
distilled water were added to the water in the cylinder. 
Within 5 minutes the paper turned brown, showing the 
presence of sulphuretted hydrogen, which therefore can 
only be attributed to the decomposition of ultramarine. 
In order, however, to ascertain the presence of any alka- 
line sulphide existing as such and not as a constituent of 
ultramarine, a large quantity of the latter was treated with 
distilled water and quickly filtered. The filtrate contained 
no sulphide. Hence the evolution of sulphuretted hydro- 
gen was really due to the decomposition of ultramarine by 
the carbonic acid. The colour of the pigment was dulled, 
but could not be destroyed completely even when metallic 
chloride existed in the solution. 
Through the kindness of Messrs. Jewsbury and Brown, I 
got a dozen bottles of aerated water, one half of which were 
charged with 2 grains of sodium chloride in each. The 
effects of these waters upon ultramarine were compared 
together week after week by putting *07 grams of the pig- 
ment into the cylinder containing these liquids. In all 
cases the following effect was observed : the decomposition 
of ultramarine did not commence at once, but on standing 
for about an hour the paper moistened with lead acetate 
solution and placed over the cylinder began to be blackened. 
