364 Whiter Cover Washes 



ten produced as good a result as a thick, but under outside conditions a 

 thick coat is necessary in order to allow for the eroding power of weather 

 conditions. 



In conclusion I have to thank Prof. Barker for much valuable 

 assistance and many suggestions. 



Abstract. 



A. These experiments were started to find a cover spray which : 



(1) Is thicker than ordinary lime wash; 



(2) Resists weather conditions; 



(3) Is cheap; 



(4) Is easily made. 



Of these a formula containing whiting, glue, starch, potassium 

 dichromate and water fulfils the first two conditions. It fails in 

 numbers (3) and (4) as its cost works out to 2d. a gallon and it is not 

 sufficiently easy to make as so much hot water is required. 



B. If lime alone is used: 



(1) It must be used when fresh. 



(2) It should be allowed, if possible, to stand for 12 hrs. before 

 application. To do this on a large scale, one-third of the total quantity 

 of water may be added first. When it is to be applied, the other two- 

 thirds can be added. This does away with the necessity of having 

 a large number of tubs. 



C. The beneficial action of lime wash on Psylla eggs is due to the 

 mechanical, sealing action rather than to any chemical one. 



