26 W. G. Mixter — Polymerization of Oxides. 



S + 3(2Na + 20) + (Ca + S + 60 + 4H) + (2Na + 0) = 

 359-4 473-9 100*3 



2(2Na + S + 40) + (Ca + O) + 4(Na + O + H) + 276-1 Cal. 

 657-2 145 407-5 



The experimental result is 169-8 + 111-6 = 281-1 Cal. 



The results with CaS0 4 aud CaS0 4 .2H 2 are somewhat 

 higher than the values derived from Thomsen's data. Whether 

 the difference is due to errors or to CaO set free from the 

 sulphate combining with sodium oxide, or to other causes, can- 

 not be determined. It has been stated that CaO made by 

 heating the carbonate gives no heat effect in the fusion. CaO 

 separated from the sulphate may be in a different molecular 

 state from the intensely heated oxide. 



The difference found between the heat effect of CaS0.*2H a 

 and CaS0 4 is 111-6 - 43-7 = 67-9. The number taken for the 

 heat of the reaction of H 2 + Na 2 is 36-1 (p. 24). For free 

 2H 2 it is 72-2. Hence for the heat of combination of 2H 2 

 with CaS0 4 we have 72-2 - 67'4 = 4-8 Cal. Thomsen's value 

 is 4-7. 



The work with gypsum has been given in detail as it 

 illustrates well the method of fusion with sodium peroxide for 

 determining the heat of combination of water. 



Brucite, MgO. H^O. — The mineral used was a good crystal- 

 line specimen. An analysis gave the theoretical quantity of 

 water, 0-3 per cent FeO, and traces of Mn and Ca. Two cal- 

 orimetric tests were made of the MgO from heating the brucite 

 with the result of 0, and 13 cal. per gram. One of pure MgO 

 gave 13 cal. Three determinations of the heat effect of brucite 

 in mixtures of sulphur and sodium peroxide gave 476, 438 and 

 456 cal. "With lampblack in place of sulphur the result was 

 461 cal. The mean 458 X 58-3 = 26'7 Cal. This number 

 subtracted from 36*1 gives 9-4 Cal. for the heat effect of 

 MgO + H 2 0. From Richards' result for the heat of solution 

 of magnesium in hydrochloric acid, Thomsen's values for the 

 heat of solution of the chloride, etc., and Yan Wartenberg's 

 Mg + O = 143-6 is derived 7"0 Cal. This value is for preci- 

 pitated Mg(OH) 2 , which is commonly regarded as amorphous. 



Ferric Hydroxide. — Ferric hydroxide after drying in vacuo 

 was found to have the composition Fe 2 3 4- 1*96 H 2 0. When 

 mixed with sodium peroxide the mixture became warm, hence 

 the preparation was not available for the calorimetric work. 

 Next ferric hydroxide was precipitated from a boiling solution 

 of the chloride by ammonia and the whole was kept hot on a 

 steam bath for several hours. The precipitate was washed 

 with hot water and dried in the open air. After pulverizing 

 it was left nine days over solid potassium hydroxide. This 

 preparation, designated as A 1 , lost on ignition 11-3 per cent and 



