99 
by themselves No. I. gave off water and became friable 
sometimes exfoliating, No. II. also gave off water and be- 
came opaque (like No. III.) and at the same time friable, 
while No. III. underwent no change. 
The general conclusions to be drawn from these experi- 
ments are that the principal difference between the three 
kinds of rods lies in the relative proportions of water they 
contain, and that the larger proportion of water contained 
in any sample, the more transparent is it. From even a 
cursory examination of the rods, it may be seen that as the 
proportion of water decreases the original features of the 
rods become more and more obliterated, so that a totally 
dehydrated rod is reduced to a mass of crystalline inorganic 
silica. It will be seen that an examination of the state of 
combination of the water in the different rods would be 
likely to throw light on their constitution ; but, owing to 
the small quantity of rods at my disposal, the method for 
thus examining substances, which I have published else- 
where,* was in this case inapplicable, an optical examination 
being the method which promised to yield the best results. 
Heating the rods with caustic soda solution did not give 
results throwing any light on their structure, the general 
effect of this reagent being to erode them, as shown 
in Fig. 1. An attempt was made to gain a knowledge of 
* Examination of Substances by the time method. Chem. Soc. Jonrn., 
No. CLXXVII. 
