358 SAGES, SHOVE SLA GLOIBIN TES 
magnesium and calcium salts which collect at the surface and 
are dissolved by the water when the samples are washed. 
Effect of carbonic acid gas—TVhe effect of carbonic acid gas 
on limestone is determined in the same manner as that of 
sulphurous acid gas. The samples are dried at a temperature of 
110° C. and weighed. They are then placed in a wide mouthed 
bottle which is filled with carbonic acid gas. A beaker of water 
is placed in) the bottle to keep thevatmosphere, moist ken 
being treated for forty-four days the samples are removed, 
washed, and weighed. The percentage of loss in weight is 
taken as the result. 
Sulphur dioxide and carbon dioxide probably do not at any 
time exist alone in the atmosphere. The effect of these gases 
acting together or in conjunction with the many less abundant 
gases of the atmosphere may produce very different results than 
when acting separately. 
Bok BUCKEYE 
GEOLOGICAL AND NATURAL History SURVEY. 
Madison, Wis. 
