180 



Allen, Crenshaw, Johnston, and Larsen- 



Table II. 

 Effect of temperature on the formation of marcasite. 



Taken 



Found 



Tem- 

 perature 



FeS0 4 . 

 7H 2 



Sulphur 



Free H,S0 4 



Water satu- 

 rated with 

 H 2 S at 0° 



Oxidation 

 number 



Percent 

 pyrite 



300° 

 300° 

 200° 

 100° 

 100° 



5g. 



5g. 

 5g. 

 5 g. 



0-5 g. 

 0-5 g. 

 0-5 g. 

 0-5 g. 

 0-5 g. 



0*17 g. 

 0-17 g. 



0-17 g. 

 0-17 g. 

 0-17 g. 



100 cc 

 100 cc 

 100 cc 

 100 cc 

 100 cc 



29-0 



28-4 



20-7 



16- 



17*2 



57-5 

 56*5 

 32-0 

 6'0 

 10*0 



Table II shows the influence of temperature on the reaction. 

 Here ferrous sulphate and sulphur, the products of the action 

 of hydrogen sulphide on ferric sulphate, were taken. The 

 quantities of acid used, by inadvertence, were considerably less 

 than intended, but the evidence shows the influence of tempera- 

 ture very plainly. The higher the temperature the greater is the 

 quantity of pyrite formed. A word is here needed on the 

 question of the formation temperature. The furnace was first 

 heated to the required temperature, then the cold bomb con- 

 taining the tube was introduced. Obviously, the reaction could 

 not take place entirely at one temperature. At the lower tem- 

 peratures, however, the reaction is very slow, so that the time 

 required for the bomb to reach the temperature of the furnace 

 is not important. When the bombs were heated to 300°, many 

 hours were required to reach the maximum temperature. It 

 would not be worth while, after having shown that the two 

 variables, temperature and acid concentration, both influence 

 the product of this reaction, to study the problem in great 

 detail, but it is interesting to note that the reaction will proceed 

 at ordinary temperatures, and also that pure marcasite may be 

 obtained by a proper combination of the two variables. Thus 

 at 100° the precipitate formed from a solution containing 

 1*18 per cent of free sulphuric acid gives the oxidation coeffi- 

 cient 14*5 and is therefore pure marcasite. From 2 liters of a 

 solution which contained 3 per cent of hydrous ferrous sulphate 

 and 0'15 per cent of free sulphuric acid, 1 gr. of precipitate was 

 obtained at room temperature in about three weeks. Unfortu- 

 ately, there was an accident in the determination of the oxida- 

 tion coefficient of this product, but we can state that it contained 

 less than 10 per cent of pyrite. For every temperature there 

 appears to be a quantity of acid which inhibits the reaction: 



