55 



I, in conclusion, express my conviction that many officially certified 

 tracings of the maps and copies from the books of this survey, issued 

 out of the surveyor-general's office before the lamentable and destructive 

 fire of 1711, are yet m existence, and lying concealed amongst the title- 

 deeds of ancient Irish landed proprietors. And I would urgently sug- 

 gest to such, as well as to their solicitors, a search for and submission 

 to my inspection of as many as may be found; when I will undertake, 

 upon unexceptionable and contemporaneous evidence, to prove the genu- 

 ineness of such as may be genuine ; and thus give authenticity and 

 weight to their documents of title, and at the same time additional tes- 

 timony to what I have already advanced of plots or maps being accompa- 

 niments or fruits of Strafi'ord's survey. 



Professor William K. Sitlliva^t read the following paper : — - 

 Ok some ctteiotjs Moleculak Chaitges peoduced m Silicate of Zinc 



BY THE APPLICATIO]Sr OF HeAT. 



In a Paper which I read to the Academy on its first meeting this session, 

 some curious pisolithic combinations of silicate and carbonate of zinc 

 from Dolores mine, near Santander, in Spain, were described. Mention 

 was also made of the presence of carbonic acid in the fibrous Smithson- 

 ite or hemi-morphite from the same locality. It was sought to account 

 for this circumstance, as well as the variation in the amount of water, 

 and its want of proportionality to the other constituents which are 

 generally observed in the published analyses of silicate of zinc, by sup- 

 posing that the carbonic acid existed as dicarbonate of zinc which was 

 in combination with disilicate of zinc. This hypothesis involved the 

 isomorphism of the silicate and carbonate, which were consequently con- 

 sidered to be capable of forming an indefinite number of compounds, 

 like the similar salts of isomorphic bases or acids. Por all these com- 

 pounds the general formula m (2ZnO,Si02) + n (2ZnO,C02) + p HO, may 

 be proposed. 



A very curious molecular change, which I have found to be pro- 

 duced in all these compounds by the action of heat, appears to me to 

 give a very unexpected support to the view regarding the constitution 

 of the silicates just stated, and consequently to the isomorphism of silicic 

 and carbonic acids, upon which it is primarily founded. When frag- 

 ments of the pisolithic silicates were heated to drive off the hydrated 

 water, they became of a bright lemon-colour, passing into orange ; on 

 cooling, the colour almost wholly faded. The phenomenon is just like 

 what is observed with white oxide of zinc, except that the latter never 

 yields so bright a yellow as the silicates do. The change appears to take 

 place at a little above the temperature of melting lead ; at a redness 

 just visible at daylight, the colour of the fragments changes to green, 

 which is sometimes of a deep verdigris-green. On removing the lamp 

 for a moment from under the crucible containing the fragments, they 

 suddenly became yellow. When the temperature was increased by 

 means of a blowpipe, the colour again became yellow. On allowing the 



