28 POPULAR SCIENCE MONTHLY. 



experimentally with gases which were intentionally much diluted, pure 

 sulfur dioxid with a large excess of air being used, and it could be 

 demonstrated that the reaction did not fully cease, under certain cir- 

 cumstances, until the sulfur dioxid was almost completely converted 

 into sulfuric acid. Strangely enough, even when double the theoretical 

 amount of air was present, it seemed to have no untoward influence 

 upon the reaction, indeed it rather appeared as if the large excess of 

 oxygen exercised a favorable effect upon the quantity of sulfur trioxid 

 obtained from a given quantity of the dioxid. From this it followed 

 that the earlier conceptions, according to which the dilution of the 

 sulfur gas was unfavorable for the contact-process, must be submitted 

 to a critical examination. 



From now on the experiments were carried out upon the gases which 

 came directly from the pyrites-burners. For this purpose the gases 

 were brought directly from the pyrites-burners to the laboratory through 

 a long lead pipe. This pipe acted as a long dust catcher, and the gases 

 in their passage through it were thoroughly freed from every mechan- 

 ical impurity, such as ashes, burner-dust, etc. The gases were further 

 passed through several bottles filled with sulfuric acid, before they 

 reached the contact mass. The experiments were very satisfactory, for 

 quite as favorable results were attained as had been the case with the 

 mixture of pure gases. No diminution in the activity of the contact 

 mass could be observed, although the experiments extended over several 

 days, and the hope seemed well justified that in this simple manner it 

 would be possible to manufacture sulfuric acid directly from the burner- 

 gases without loss of sulfur. 



The experiments were now carried out on a larger scale. Here, 

 however, it soon appeared that the activity of the contact-mass rapidly 

 diminished in strength and finally ceased. The results were the same, 

 even after the gases had been not only purified as in the laboratory ex- 

 periments, by cooling in long tubes and washing repeatedly with sul- 

 furic acid, but in addition had been passed through a dry coke and 

 asbestos filter; they were then as pure as was technically possible. We 

 were, therefore, obliged to consider the experiments on a large scale as a 

 failure. 



Although by these unlooked-for results a hard blow was given to the 

 hope of success, nevertheless further experiments were undertaken in 

 the laboratory for the purpose of investigating the cause of the appar- 

 ently inevitable deterioration of the contact-mass. 



The surprising observation was soon made that there are substances 

 which, when present in exceedingly small quantities, are capable of 

 inhibiting the catalytic action of platinum to an extraordinarily great 

 degree. Among these substances are first of all arsenic, mercury and 

 phosphorus, while antimony, bismuth, lead, iron, zinc and the other sub- 



