Effect of Temperature, Acidity, etc. 



409 



was at first believed that the quantity of sulphide precipitated 

 below the maximum temperature would decrease regularly 

 with the increase in acidity, since the total quantity of product 

 obtained at different temperatures diminished with the acid 

 concentration. But experiment has shown that the relation is 

 not so simple as that, and the question arises : Why are the 

 final products at these maximum temperatures so simply 



Fig 2. 



350 



300 



L. 



^200 



(0 



L. 



a) 

 a. 

 E 



100 



j^_ — ■ o 



5 10 



Time in hours 



15 



Fig. 2. Typical curves showing time required for a cold bomb to reach 

 the temperature of the furnace. 



related to the acidity ? The most plausible explanation is that 

 the influence of temperature is comparatively small in the 

 interval in which precipitation occurs. We can get no ade- 

 quate measure of this by comparing the curves for 200° and 

 300°, for experiment shows that when the furnace is set for 

 300° most of the product is precipitated (i. e., the hydrogen 

 sulphide is nearly used up) by the time the maximum tempera- 

 ture is reached. Until we have more knowledge or can bring 

 about precipitation at a constant temperature we can not state 

 quantitatively the influence of either temperature or acidity. 

 What we do know is the direction and regularity of both 

 influences. It will be noticed in the figure (fig. 1) that the 

 two lines representing the composition of sulphides from vari- 



