No. 6. DEPARTMENT OF AGRICULII^RE. 505 



and fruit than when a smaller quantity is properly put on. To many 

 I Ills may seem strange. But nevertheless it is a fact, and an at- 

 tempt will be made to show just how it comes about. 



In order to do this it will be necessary to study in detail what takes 

 place in the drops of water after they leave the nozzle and become at- 

 tached to the fruit or leaves. It will be remembered that the ma- 

 terial is to be kept in suspension and equally disseminated through- 

 out the whole mass of liquid in the tank. Consequently, each minute 

 globule of water as it leaves the nozzle will carry with it a certain 

 amount of suspended Paris green, Bordeaux mixture, or both, as the 

 case may be. Now, the settling which goes on in the spray tank 

 takes place also in the globule of water after it becomes attached 

 to the leaf or fruit. Therefore, it i® desirable to have each globule of 

 water deposit its suspended material at the place where it is attached 

 to the fruit. But liquids have what is known as "surface tension;" 

 that is a force exerted from within which tends to keep a small 

 globule of water intact. Beyond a certain size this force is unable 

 to keep the globule intact as such. Then it will not remain where it 

 strikes the surface of the fruit or leaf, but vdll run down to the low- 

 est point and there drip off. This happen® when the globules are too 

 large or if the smaller ones are brought so close together that they 

 run together to form one or several large ones and the same running 

 dow-n and dripping-off results. This running-together may be easily 

 seen by breathing against a cold window pane. First, it will be 

 noticed that the globules of condensed moisture are exceedingly 

 small, each one, however, remaining separate and distinct. Now 

 continue breathing against the moist spot. The globules of mois- 

 ture increase in size until a point is reached where they run together 

 and form one large globule spread over the surface of the glass. 

 But now, instead of remaining spread over the glass, when it is in a 

 vertical position, the large globule runs to the lower edge of the pane, 

 and if there is moisture enough, will drip off. 



This is exactly what takes place on the surfaces of leaves and fruit 

 when the spray liquid is applied. The globules are at first deposited 

 as separate, fine "dew drops," covering the entire surface. This is 

 the ideal point to be reached, and as soon as it has been accomplished 

 no more liquid should be applied. If more is put on, the small drops 

 run together and trickle down to the lowest point. It has been said 

 that the settling of the material takes place in the globule of water 

 after it becomes attached to the fruit. The larger the globule, then, 

 tile more settling will take place. It has also been seen that the 

 settling goes to the lowest point. Consequently, if the globule is 

 spread over a large portion or the entire surface, the settling will 

 naturally go to the lowest place in this instance also, and as the low- 



