of Dried Hydrogen Sulphide Gas. 473 



the experiment was 07235 gram ; and after the gas had 



passed was 0*8435 gram, or an increase of 0*1200 gram. 



Thus it is seen that the ratio of the increase when water is 



present with the magnesia is to the increase in weight in the 



absence of water as 



1200: 31 , , , nf; o 



1 900 • Qf^^ temperature ot 15 . 



1200 : 11 at 40°. 



The reason for the addition of liquid water to the oxide, 

 instead of saturating the gas with moisture, is because 

 Eichardson has shown (J. C. S. li. p. 801) that in analogous 

 reactions the water as steam has no influence on the chemical 

 change. 



Similar results were obtained with monoxide of barium, 

 although the increases were slightly greater than in the case 

 of magnesia. Thus in an experiment made at a temperature 

 of 15° the weight of oxide of barium taken was 1*7465 gram, 

 which, after the passage of the hydrogen-sulphide gas, showed 

 an increase of 0*0034 gram. 



Another experiment was conducted at a mean temperature 

 of 90°. The weight of oxide taken was 3*3735 grams, which, 

 after the passage of the gas and subsequent displacement by 

 hydrogen, was found to weigh 3*3787 grams, or an increase 

 of 0*0052 gram. Hence it appears from these experiments 

 that dried hydrogen sulphide has no action on dried monoxide 

 of barium between the temperatures of 15° and 90°. 



With sesquioxide of iron the change that takes place is more 

 evident than with any other oxide yet examined : although 

 the results so far obtained point to the conclusion that with 

 perfectly dry materials no change would take place*. In one 

 experiment 5*8108 grams of sesquioxide of iron showed an 

 increase in weight, after the passage of the gas, of 0*0832 

 gram. The methods adopted for drying the oxide have not 

 been sufficiently etfectual to ensure complete absence of 

 moisture, and the minute change that does take place is doubt- 

 less initiated by a trace of moisture already present f. 



Experiments of a somewhat different character to the fore- 

 going were then undertaken. Instead of determining the 



* The reaction between hydrogen sulphide and this substance presents 

 the particular interest that it is of daily application in the purification of 

 coal-gas. L. Wright [J. C. S. 1883, p. 156J in his experiments upon this 

 point seems to have used the hydrated oxide only. 



t Professor Odling tells me that although dried hydrogen sulphide 

 does not act on the ordinary oxide of iron under the conditions of these 

 experiments, yet an oxide of iron can be prepared which is acted upon by 

 the gas : thus the compound Fe. 2 3 CaO, got by fusing calc-spar and oxide 

 of iron together, is such a body. 



