Mixter — Heat of Formation of Titanium Dioxide. 45 



Art. VII. — The Heat of Formation of Titanium Dioxide / 

 by W. G. Mixter. 



[Contributions from, the Sheffield Chemical Laboratory of Yale University.] 



In 1909 the writer determined the heat of formation of tita- 

 nium dioxide by the sodium-peroxide method. The value 

 found at that time was 215,600 c .* In an article f which 

 appeared shortly after the writer's, Weiss and Kaiser gave the 

 results obtained by them by burning titanium in oxygen. The 

 average of their experiments is 97,772 c for the heat of forma- 

 tion of titanium dioxide. It will be seen that the value found 

 by them is less than 50 per cent of the value found in this 

 laboratory. This great difference led the writer to attempt the 

 burning of titanium in oxygen. 



A preliminary test showed that a platinum tray or cup would 

 not answer for holding the metal in the bomb since the heat of 

 the combustion melts platinum. Furthermore it seemed best to 

 have the particles of titanium separated as much as possible to 

 insure complete oxidation. With this object in view the fol- 

 lowing method was used. A weighed amount of cotton wool 

 was placed in the hemispherical bottom of a sterling silver 

 bomb having a capacity of 100 ec , and titanium in grains or 

 powder was scattered over the cotton. The ignition was by 

 means of a cotton thread suspended from a small wire connect- 

 ing the electrodes in the bomb. The cotton wool burned 

 instantly and scattered and ignited the metal. After the com- 

 bustion the titanium oxide was found mostly in one globule 

 sticking to the bottom of the bomb. It was white on the out- 

 side but dark colored and crystalline on the fractured surface. 

 In all cases the large globule was hollow, an indication of slight 

 dissociation of the oxide with sudden fall of gas pressure owing 

 to cooling. The titanium used in experiments 1 to 5 was from 

 the same pulverized metal used in the work two years ago. It 

 was ground again in an agate mortar and separated by sifting 

 into two lots, one of grains a millimeter and less in diameter 

 and one of powder. The former was used in the first three 

 and the latter in the fourth and fifth experiments. It was 

 shown in the previous paper that the metal was quite pure. 

 The low calorimetric results obtained with the powdered sample 

 raised the question of its purity and therefore it was analyzed. 

 By the pyrosulphate method 0*4765 gram of the powder gave 

 97'2, and by solution in hydrochloric acid and precipitation 

 with ammonia 0*2025 gram gave 96*4 per cent of titanium. 



* This Journal, xxxii, 393 ; abstract in Zentralblatt, ii, 180, 1909. 

 fZeitschr. anorg. Chem., lxv, 397. 



