W. G. Mixter — Polymerization of Oxides. 31 



simple molecular ratio between the water and the ferric oxide. 

 Furthermore, Professor Foote, in an investigation which will 

 be published later, has found that part of the water in ferric 

 hydroxide, precipitated and washed at common temperature, 

 behaves in freezing like capillary water. 



Titanium Dioxide. — Titanium hydroxide precipitated by 

 ammonia, dried at 100°, contained 6*7 per cent of water, and 

 after heating for a day at about 160°, 5 per cent. It was 

 finally heated three days to 225 — 240°, losing the last day less 

 0*1 per cent. The preparation lost on ignition in two deter- 

 minations 2*23 and 2*24 per cent. The results of fusion with 

 sodium peroxide were 702 and 688, mean 695 cal. for the heat 

 effect of 1 g. of the substance containing 0-978 g. of Ti0 2 and 

 0*022 g. of water. Assuming that the water content reacts in 

 the fusion as free water, we have 



695 — (0-022 X 2000) -f- 0-978 = 666 cal. 



The heat effect of ignited titanium dioxide was found* to be 

 629 cal. Hence (666-629) X 80 = 3-0 Cal. for the heat effect 

 of the condensation of titanium on ignition. If it be assumed 

 that the heat of union of water with titanium dioxide equal the 

 heat effect of Na 3 + H 2 the result is 6-0 Cal. Hence tita- 

 nium dioxide, holding 2-2 per cent of water at about 240°, 

 evolves between 3 and 6 Cal. on ignition. 



Silica. — Silicic acid was made by adding hydrochloric acid 

 to a solution of sodium silicate and evaporating to dryness on 

 a steam bath. After washing and drying it was heated a day 

 at 360-400°. The preparation contained 3-8 per cent of water. 

 Two determinations of the heat effect of 1 g. fused with sodium 

 peroxide gave 1268 and 1207, mean 1237 cal. Some years ago 

 I found for ignited silica 1185 and 1182, mean 1183 cal. 

 These values indicate that silica polymerizes at high tempera- 

 tures with small heat effect. 



■Zinc Oxide. — De Forcrandf made a thorough investigation 

 of zinc oxide. His results for the heat of formation of the 

 oxide prepared at increasing temperatures are 80*29, 82*98, 

 84*50 and 84*70 Cal. 



In conclusion, attention is called to the uncertainty in the 

 derived heats of combination of water with the oxides of the 

 heavy metals given in the following table : 



* This Journal, xxvii, 393. 



f Ann. Ch. Phys. (7), xxvii, 26, 1902. 



