i9o6] AS A FUNGICIDE. 161 



The table sHows that when sulphur is heated very slowly with 

 free access of air a large percentage (nearly one-third) of the 

 vaporized sulphur is converted into sulphuric acid, very little or no 

 sulphurous acid being formed. When the temperature is increased 

 and the sulphur more rapidly vaporized, the percentage of sul- 

 phuric acid formed is very much smaller, the percentage of sul- 

 phurous acid formed remaining about the same. When the sulphur 

 is heated rapidly with access of less air the proportion of sulphurous 

 acid is increased while the percentage of sulphuric acid formed is 

 very much lessened. It is of course difficult to carry on an experi- 

 ment for collecting the gases formed which would at the same time 

 simulate the conditions in a greenhouse where there is free access 

 of air and the temperature is comparatively low. But the results 

 of my experiments as given in the table would lead to the inference 

 that a large percentage of sulphuric acid would be formed and very 

 little or no sulphurous acid, as shown in experiments 8 and 9. 



While it is known that sulphurous acid has marked germicidal 

 properties and while a small percentage of sulphurous acid is pro- 

 duced when sulphur is heated under certain conditions, still owing 

 to the large percentage of sulphuric acid produced when sulphur 

 is heated under conditions which more nearly simulate those where 

 sulphur is heated on steam-pipes in the green-house, the question 

 arose as to whether sulphuric acid has not marked fungicidal action 

 and as to whether it is not one of the active agents when sul- 

 phur is used as a fungicide. In order to determine w^hether sul- 

 phuric acid has fungicidal properties a number of experiments were 

 carried out. 



Spraying Experiments. 



During the summer of 1904 some preliminary experiments were 

 conducted to determine what strength of solution of sulphuric acid' 

 could be used for spraying plants without injurious effects. In this 

 series of experiments the solutions were made with distilled water, 

 and used in strengths varying from i part in 200 to I part in 10,000. 

 The plants experimented with were the common field plants, such 

 as wild cherry, elder, ailanthus, Phytolacca, yellow dock, burdock, 

 abutilon, blackberry, wild rose, milkweed, locust, etc. x^n ordinary 



