1890.] Col. "Wafcerhou.'?e — Agale-lllce furmatiuu in Silicate of Soda. 177 



but whether light has had anything to do with the decomposition of 

 the solution and the formation of the deposit, it is impossible to say, 

 and it is uncertain even whether the side of the bottle which shows 

 the formation was continuously exposed to light. 



Towards the end of 1883 a fire took place in the room in which this 

 bottle was kept, and it and other chemicals in the same place were 

 exposed to a very gi'eat heat in a closed-up room. I did not at the time 

 notice any change in the silicate solution — nor do I recollect when I 

 first did notice the formation, but it was at least some three or four years 

 ago : the deposit was then well formed, and no particular change has been 

 noticeable since, except that the upper part of the solution, which then 

 was clear, is now clouded and beginning to solidify. The bottle ap- 

 pears never to have been opened since it came, but it is now cracked in 

 the upper part and air might have access to the contents. The bottle 

 may have cracked from the heat at the time of the fire. 



I am indebted to Dr. W. King and Mr. Lake of the Geological 

 Survey for kindly helping me in looking up the literature of the sub- 

 ject, and from a memo, by the latter, it appears that solutions of alkaline 

 silicates are prone to deposit silica in a gelatinous form by keeping. 

 In one somewhat similar case of deposit in a bottle, the deposit contained 

 97-G Si Og and 2-4 Na Og in 100. 



The causes that bring about this deposition are : — 



(1.) Cooling of the solution. 



(2.) Evaporation. 



(3 ) Access of air containing COo. 



(4.) Contact with certain silicates (e. g., glass) in which the acid 

 is not saturated and which therefore tend to remove alkali from the 

 solution (?). 



(5.) Silica is also precipitated by almost all acids and many salts. 



Except in the case of the fire the solution has been exposed to no 

 extremes of temperature, beyond the ordinary seasonal changes between 

 60° and 94° ; so that cause (1) could not have had any very great effect 

 in producing the change except at the time of the fire. 



The bottle having been closed there has been no sensible evapora- 

 tion, nor except by the crack could air with COg have had access to the 

 solution and then only in veiy small quantities. No acids or other re- 

 agents have been added — so that the only remaining possible cause of 

 the deposition of silica is the decomposition of the glass of the bottle 

 itself, and this seems most probable. 



Herr 0. Maschke, who has particularly studied the separation of 

 crystallised silica from watery solutions (see Pog. Annalen, cxlv), does 

 not appear to have noted upon depositions by lapse of time, as in the 



