4:8 Mixter — Heat of Formation of Titanium Dioxide. 



titanium is over 200,000 c . The mean of all of the results for 

 the heat effect of 32 grams of oxygen combining with titanium 

 is 218,500 c . Excluding those of experiments 4 and 5 with the 

 finely powdered metal, the composition of which is not accu- 

 rately known, the mean is 218,000 c . The last two results are 

 to be regarded as the best, as larger quantities of metal were 

 used and the method employed for finding the amount of oxy- 

 gen required to complete the oxidation was more accurate than 

 the one used in the other determinations. The last two results 

 give for Ti 4- 2 = Ti0 2 (crystalline) 4- 218,400 c . This is 11 

 per cent higher than found two years ago by the sodium- 

 peroxide method,* which was 215,600 c , for the heat of forma- 

 tion of amorphous titanium dioxide. 



Note on the Spontaneous Oxidation of Titanium in the Air. 



The powdered titanium mentioned on page 45 contained not 

 over 97 per cent of metal. Another sample prepared from a 

 lump of pure titanium was ground in an agate mortar from time 

 to time. Then 2*028 grams were left for four months in a small 

 loosely stoppered vial. At the end of this period the weight 

 was found to be unchanged. Analyses were made as follows : 

 One portion, 0*3067 gram, was dissolved in a beaker in hydro- 

 chloric acid and a few drops of nitric acid were added and the 

 solution was evaporated to dryness. Then the residue was dis- 

 solved in hydrochloric acid. The solution was complete. 

 Finally the titanic acid was precipitated by ammonia, washed, 

 ignited, and weighed with the usual precautions. Another 

 portion, 0-3119 gram, was dissolved in a platinum dish in hot 

 concentrated sulphuric acid, to which a few drops of nitric 

 acid were added. The solution was complete. The analysis 

 was carried out as just described. The two results were 

 respectively 96*6 and 97*1 per cent of titanium. 



The 3 per cent of oxygen found by difference corresponds 

 to 7*5 per cent of dioxide or 12 per cent of monoxide of 

 titanium in the powders analyzed. As only clean fragments 

 of pure metal were pulverized, the conclusion is that titanium 

 oxidizes superficially in the air. Since the metal does not 

 gain weight, in time the oxide forms a protective coating. The 

 only statement that I have found in the literature bearing on 

 the question is one in Abegg, III, ii, p. 407, that Schneider 

 found that titanium heated for 15 hours at 100°-120° gained 

 in weight 0*06 per cent. 



* Loc. Git. 



