1922] 



YOUNG THE TOXIC PROPERTY OF SULPHUR 429 



part of the country. To accomplish this the material must yield 

 readily the toxic compound, pentathionic acid. The reaction 

 must be kept slightly acid (P H 4.0-5.5), as this toxic compound 

 is destroyed above or below this point. It must be readily oxidiz- 

 able at ordinary temperatures. It should have great adhes- 

 iveness; it must not burn the leaves. 



Colloidal sulphur has all these properties when tested in the 

 laboratory and greenhouse. It is almost impossible to wash it 

 from the leaves of plants after it has dried. It is difficult to 

 remove it with a strong stream of water. Certainly rain would 

 have little effect upon it. 



That colloidal sulphur is readily oxidized has been demon- 

 strated in the foregoing experiments. Kuhl ('21) states that col- 

 loidal sulphur bears the same relation to atmospheric oxygen as 

 phosphoric iron, the latter being self-inflammable. 



Methods for the preparation of colloidal sulphur mixtures for 

 fungicidal use are being experimented upon. The hydrophilic 

 colloidal sulphur prepared by the method given above is suitable 

 as a spray. It did not burn the leaves of bean, potato, tobacco, 

 rose, and geranium when sprayed on them. By the use of commer- 

 cial materials this mixture is not too costly for practical purposes. 

 Other methods for its preparation are being tried. 



The method for the preparation of hydrophobic colloidal sul- 

 phur for trials in the greenhouse was as follows: One gallon 

 of commercial or home-made lime sulphur was diluted with 5 gal- 

 lons of water. Commercial phosphoric acid was added until the 

 reaction was slightly acid. A milky precipitate of colloidal sul- 

 phur was formed. The mixture was allowed to stand a day or 

 two to remove excess H 2 S, and then applied. The advantage of 

 phosphoric acid over other acids is that the calcium acid phos- 

 phate formed maintains the proper reaction. This mixture diluted 

 1:5 with water prevented the germination of Botrytis cinerea and 

 Colletotrichum Gossypii in aerated cultures. When sprayed on 

 the plant this type of colloidal sulphur does not stick as well as 

 hydrophilic colloidal sulphur but no doubt can be made just as 

 effective a spray by the addition of soluble glue or other suitable 

 spreaders. Any precipitated sulphur to which has been added 

 calcium acid phosphate or another suitable compound for main- 

 taining the slightly acid reaction should be an effective fungicide. 



With respect to increasing the value of flowers of sulphur as a 

 spray the writer is not yet prepared to make a definite recom- 



