BIRTH AND ZAPTINITIES OF -CRYSTALS 123 
at a higher temperature than that corresponding to the appear- 
ance of the second shower in an open vessel. For example, a 
48'2 per cent. solution of sodium nitrate is saturated at 26°, and 
yields the dense shower at 16°; a 51 per cent. solution is saturated 
at 39°, and yields the dense shower at 30°; and these solutions 
enclosed in sealed tubes only yield a shower on shaking at 16° 
and 30° respectively. 
During the visit of the British Association to South Africa 
X 
t 
L] 
| 
L] 
1 
t 
i 
t 
Temperature. 
oO 50 p 
Concentrator. 
ETC wr. 
I carried sealed tubes containing these and other solutions with 
me, and during several weeks kept the first solution between 
the temperatures of 26° and 16°, and shook it violently at inter- 
vals without causing crystals to appear. But as soon as the 
temperature fell to 16° the solution began to crystallise. 
We conclude, therefore, that in an open vessel such a 
solution crystallises at 26° only because the liquid is inoculated 
by crystal germs from the air, and that it crystallises again at 16° 
because fresh crystals appear spontaneously or are born in the 
