148 SCIENCE AND FRUIT GROWING 



gallons. In the Oregon wash, about i Ib. of caustic soda is added 

 in addition to the above materials, and the heat generated on 

 adding water to the mixture is sufficient to obviate the applica- 

 tion of external heat. A wash of this strength can be used only 

 on dormant trees, and is then more effective when applied hot ; 

 but at a lesser strength it is now being used on trees in leaf, 

 chiefly as a fungicide. The wash always contains a considerable 

 proportion of unaltered lime, the sulphur going into solution as 

 calcium thiosulphate and pentasulphide. The latter undergoes 

 rapid change, even in absence of air, the pentasulphide becoming 

 converted into thiosulphate with the liberation of sulphur, and 

 the thiosulphate into sulphite and more free sulphur : the 

 sulphite ultimately oxidises to sulphate. Where caustic soda is 

 used in its preparation, the sulphur reacts with it in preference 

 to the lime. The method of operation of this wash is uncertain. 

 It is used habitually in the Western States of America for com- 

 bating San Jose scale, and according to certain experiments, 

 none of the substances which it contains, when used separately, 

 have any effect on the scale ; according to other authorities, a 

 mixture of potassium sulphide and lime is as effective as the wash. 

 It appears that its action is in part mechanical, the sulphur 

 deposited from it on to the trees glueing the scales to the bark, 

 and preventing the egress of the young insects. What function 

 the salt performs is obscure, and, according to some investigators, 

 it may be omitted without detriment. Owing to the excess of 

 lime present in it, and to the destructive action of sulphides on 

 lichen, etc., the wash is a good detergent. 



Lime and sulphur mixed with water without heating are 

 sometimes used for aphis, mites and red spider, being preferable 

 to sulphur by itself ; such a mixture always contains some pro- 

 ducts of the interaction of the two substances. Calcium sulphide 

 solution is also used for the same purpose, but potassium sulphide 

 is preferable, as soft soap can be added to it without causing 

 decomposition : 3 to 10 ozs. in 10 gallons are the proportions 

 recommended. It can also be mixed with an emulsion of 

 paraffin oil. 



(4) Phenol, either dissolved by itself in water, or with the 

 addition of soap or glycerol, has been tried as a general insecticide, 

 without much success ; but a solution of carbolic acid soap is 

 very effective for certain aphides, as well as for mildews (e. g. 

 of roses), and phenol figures as one of the ingredients of several 

 proprietary insecticides which are now in use. 



(5) Paraffin oil has been found to be a most valuable insecticide, 



