HOW SULPHUR ACTS. 45 



drawbacks which sublimed sulphur has of grilling the leaves and 

 irritating the eyes of the operatois. it has been ground with inert 

 bodies capable of neutralizing the acids which it contains. Neutral 

 mixings, with a much more gentle action on the plant, .and which act 

 in the same way as the neutral sulphur above described, are thus 

 obtained. It is thus that mixtures containing gypseous, bituminous, 

 calcareous ingredients are met with, which have at the same time 

 the advantage of favouring adherence in rainy weather. Many pre- 

 parations are used in the south of France, and in Algeria, where they 

 are specially applied for August treatment ; but a larger amount must 

 be used in inverse proportion to the sulphur content. It was in- 

 teresting to know the action of sulphur on fungi living as parasites on 

 plants, and several scientists devoted themselves to this study. It is 

 recognized that the destruction of the parasite is more rapid the 

 warmer the weather. With a temperature of 30°-40° C. (86°-104°F.) 

 destruction occurs in one to three days ; from 25° C. to 30° C. (77°-86° 

 F.) it is already slower and takes four to five days ; below 25° C. (77° F.) 

 it is still more slow. According to Mach, Vesque, Sorauer, Hollrung 

 and Dufour, this action of sulphur on the mycelium of fungi results from 

 the formation of sulphurous acid, formed by the slow combustion of 

 sulphur under the action of the sun and heat. Pollacci, on the other 

 hand, believes that the sulphur is transformed into sulphuretted 

 hydrogen, the vapours of which have a very energetic action on fungi. 

 The third opinion is that of Mares and Mohr, who believe that the 

 sulphur acts of itself, i.e. by its own vapour. The first hypothesis 

 seems in fact inadmissible, for the simple reason that the sulphur 

 cannot be transformed into sulphurous acid except at high tempera- 

 tures and only by its combustion. But the sulphur does not act only 

 on the mycelium of the fungi where it is in contact with it ; sulphur 

 placed at a distance acts equally well. Spread on the soil around 

 the plant, it acts perfectly well if the temperature reaches 25°-30° C. 

 (77°-86° F.). This observation was noted as regards greenhouses by 

 Bergmann, Lord Eothschild's gardener in 1853, and by Viala, for 

 vines in the open air. If it be therefore recognized that sulphur 

 acts by the vapours which it emits, the nature of such vapours remains 

 to be examined. Sulphurous acid must not be dreamt of ; xo^o o^^ 

 of this acid in the air would burn the leaves. In warm and cold 

 greenhouses where the plants are unceasingly exposed to the vapours 

 of the sulphur emitted from the sulphur spread on the soil, these 

 would not resist long if the ambient air contained sulphurous acid. 

 The effects of this acid, to be examined further on, are disastrous to 

 plants, and if it be admitted that sublimed sulphur burns plants, this 

 drawback is only due to the presence of sulphurous and sulphuric 

 acids. The formation of sulphuretted hydrogen is equally impossible. 

 To determine of what the nature of the vapours emitted from sulphur 

 when it is spread on the leaves and the soil and exposed to the 

 action of the air and the sun may be at temperatures of 25°-40° C. 

 (77°-104:° F.), the author (Bourcart) made a series of laboratory experi- 

 ments. Sulphur mixed with dry or moist soil with or without humus 

 was placed in flasks with a tubulure. After having arranged these 



