OF GASES AT HIGH EXHAUSTIONS. 
415 
may not in reality be a trifle higher. The reason of its being only sometimes visible 
may be accounted for by a difference in the sensitiveness of the eye at different times, 
or by a difference in battery power. This, however, cannot be the whole explanation, 
for other lines are not found to vary in the same manner. 
676. The curve of repulsion exerted by radiation is plotted in dots on diagrams B 
and C. It is much lower than in oxygen or air, and sinks rapidly after the maximum 
is passed. 
VISCOSITY OF CARBONIC ANHYDRIDE. 
677. Several processes have been tried for the preparation of this gas, to avoid the 
collection over water, and consequent risk of admixture with air. The best methods 
are the ignition of bicarbonate of soda, and the decomposition of marble by hydro¬ 
chloric acid. The bicarbonate of soda plan has two great advantages : the generation 
of gas can be conducted in the sealed-up and exhausted apparatus, and nothing else 
but carbonic anhydride and water are given off. The amount of water, however, 
proves a serious inconvenience, as it uses up so much phosphoric anhydride,—therefore 
the production of the gas from marble and hydrochloric acid was finally employed. 
The apparatus is shown in fig. 13. 
