of Phosphorus and Sdlfid r ; &c ' 4*5 
protoxide of manganese, and when heated strongly, it gives on 
its water and becomes a dark olive oxide. 
It has been often suspected, that the contraction of volume 
produced in the pure earths by heat, is owing to the expulsion 
of water combined with them. The following fact seems to 
confirm this suspicion, and offers a curious phenomenon. 
Zircona, precipitated from its solution in muriatic acid by an 
alkali, and dried at a temperature below 300% appears as a white 
powder, so soft as not to scratch glass. When heated to 
700° or 8oo°, water is suddenly expelled from it, and notwith- 
standing the quantity of vapour formed, it becomes at the 
moment red hot. After the process, it is found harsh to the 
feel, has gained a tint of gray, its parts cohere together, and it 
is become so hard as to scratch quartz. 
