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WINTER COVER WASHES {conclusion). 



By A. H. LEES, M.A., 



Plant Pathologist, University of Bristol, Agricultural and 

 Horticultural Research Station. 



At the end of the season 1913-14 the most satisfactory mixture 

 found for covering and adhesive properties was one containing whiting, 

 starch, glue and potassium dichromate. It had, however, two distinct 

 disadvantages, first that hot water was required and second that its 

 cost was too high. Accordingly in the season 1914-15 fresh attempts 

 were made to find a mixture that did not labour under these 

 disadvantages. 



So far all substances that had been added to lime to increase the 

 adherence of the mixture had had the opposite effect. Either they had 

 caused brittleness or softness. What was clearly wanted was some body 

 that would serve to tie the lime particles together without itself becoming 

 crystalline or gritty when dry. In other words some suitable colloid 

 substance seemed the most hopeful body to search for. Of these glue, 

 starch, casein, resin and humus bodies immediately suggested themselves. 

 It was clear from the beginning that only substances sufficiently cheap 

 need be tried,, as comparatively large quantities would have to be used 

 in practice. 



Glue had already been ruled out owing to its being rendered in- 

 soluble by lime but the others were given a trial. Starch mixes well 

 with lime. The heat of the slaking lime can be used to gell the starch 

 so that no hot water is required. It causes considerable thickening 

 of the mixture and gives a hard and brittle coat. Table I (4). 



Subjected to rain outside it becomes gelatinous and is soon washed 

 off. It is therefore unsuitable. Resin was next tried. This could 

 be incorporated in two ways. It could be added to the lime during 

 slaking, in which case it did not increase the adhesiveness of the coat 

 though neither did it detract therefrom, or it could be first boiled with 



