158 KRAEMER— DILUTE SULPHURIC ACID [April 20 



using it. It is generally considered ^by plant pathologists that when 

 sulphur is used in a powdered form as a remedy for plant diseases, 

 the effects are due to sulphur dioxide. While sulphur dioxide un- 

 doubtedly does have a powerful fungicidal action, it is usually con- 

 ceded that sulphur dioxide and sulphurous acid are exceedingly toxic 

 to higher plants as well. Owing to the high temperature at which 

 sulphur inflames (260° C.) and the rapid evolution of sulphur diox- 

 ide, as well as its unequal diffusion, sulphur is never burned in 

 order to secure its fungicidal effects, but is employed either in the 

 form of a powder, or by gently heating it, when a certain portion of 

 it is sublimed, thus distributing it over the plants in a finely divided 

 state. In Italy the grape-growers and horticulturists have found 

 that the efficiency of powdered sulphur when dusted on plants is in 

 direct ratio to the degree of fineness. 



It is stated by Bloxam^ that '' finely divided sulphur, especially 

 sublimed sulphur, is gradually oxidized and converted into sulphuric 

 acid when exposed to moist air." It is also well known that sublimed 

 sulphur contains a certain amount of sulphuric acid. Not only is this 

 true, but it is claimed that if the sublimed sulphur be not dried after 

 washing it to free it of acid, sulphuric acid is again formed. Fur- 

 thermore, it has been shown by Pollacci- that, independent of the 

 presence of organic matter, sulphur is changed directly into sulphuric 

 acid when mixed with the soil. 



The fact that sulphur is easily oxidized in a moist atmosphere to 

 sulphuric acid taken together with the fact that sulphur when vapor- 

 ized on steam pipes is more efficient as a fungicide than when the 

 flowers, or flour, of sulphur are dusted on the plants, led to the sup- 

 position that this increased efficiency might be due to the increased 

 proportion of sulphuric acid formed. Accordingly, experiments 

 were undertaken to determine what- compounds are formed when 

 sulphur is slowly heated. An apparatus was constructed for heating 

 sulphur and for collecting the gases formed. The apparatus for 

 collecting the gases consists of a bell jar connected with two U-tubes. 

 The bell jar is suspended over a plate in such a manner as to permit 

 of the free entrance of air from below, or at a distance of 5 to 10 cm. 



^ Bloxam's Chemistry, seventh edition, 1890, p. 189. 



' Pollacci, Ga2. chini. ital., through Jour. Pharm. Chim., 1874,' p. 330. 



