248 THE EVOLUTION OF LIFE 
curdy deposit”; while in two tubes which contained 
an originally clear solution of boric acid with 
ammonium phosphate, after a similar heating the 
fluid was found to have become ‘‘ rather turbid, with 
a comparatively large amount of a fine whitish 
sediment.” Again, specimens of sea-water heated to 
160 C. for twenty minutes, “became opalescent, 
and several small whitish shreds were to be seen in 
each of three tubes.” In other cases no such change 
has occurred, though here, as in the instances above 
cited, the tubes were composed of the same kind 
of soft German glass. It is needful to mention this, 
because other experiments have shown that the use 
of different kinds of glass may also alter the results 
of mere heating. ‘Thus, recently, three tubes con- 
taining fresh sea-water were heated at the same time 
to 120 C. for ten minutes. Two of the tubes were 
of common glass, and in them the sea-water after the 
heating was found to have remained quite clear and 
free from deposit; while in the third, which was of 
uviol glass, the fluid was full of very minute glitter- 
ing iridescent scales. Again, a faintly acid sodium 
silicate solution, after having been heated to 100° C. 
for ten minutes in a uviol tube, showed at first no 
apparent deposit of silica, and only a very little 
appeared later on; and, when the fluid was examined 
on the fourteenth day, it was found to be slightly 
alkaline, rather than appreciably acid, as it should 
have been in a tube of common glass. 
