284 DISEASES OF TROPICAL PLANTS CH . 



Most plants will stand some certain strength without 

 danger to foliage, as, for example, the apple will stand 

 a solution of 1-01 specific gravity. 



Every variety of plant should be tested by treat- 

 ment of one or two plants before any wholesale 

 spraying is done. As soon as a solution is formed that 

 is safe, its specific gravity should be taken and whole 

 numbers of plants treated with a solution of like 

 density. 



The process of dilution is well described by J. P. 

 Stewart in Bulletin No. 99 of the Pennsylvania 

 Experiment Station, and is as follows : 



THE PROCESS OF DILUTION 



111 the application of any concentrate, either home- 

 made or commercial, it is essential that a definite 

 method of dilution be followed. Two solutions may 

 look exactly alike and yet differ widely in density, so 

 that any accurate method must be based primarily on 

 the density of the concentrate that is being diluted. 

 Moreover, we believe that recommendations based on 

 the density of diluted spray are preferable to those 

 based on the number of dilutions, even when accom- 

 panied by a statement of the concentrate's density. 



Accurate dilution is very simple and easily accom- 

 plished with the aid of a hydrometer having a specific 

 gravity scale. (The presence of foreign soluble materials 

 or of much roily sediment in the sample will vitiate the 

 test, a fact which may be taken into account the 

 former especially in solutions of unknown preparation. 

 Also, for exact work the temperature of the concentrate 

 should be within about 10 of that stated on the 

 outside of the instrument.) Sprays of any desired 

 density may be obtained from any concentrate by 

 .simply getting the reading of the concentrate and 

 dividing the decimal of this reading by the decimal of 

 the spray desired. For example, if the reading of the 



