The Spraying of Orchards. 121 



"but it might not be equally efficient against the apple scab. The 

 Italian growers also confess to the necessity or making a greater 

 number of applications when such dilute mixtures are used. 



The experiments of Sostegni, some of which have already been 

 referred to in a former bulletin, * have a direct bearing upon this 

 subject. In a later article f he emphasizes the value of having a 

 certain amount of dissolved copper present in the Bordeaux mix- 

 ture. The chloride of ammonia is added to increase the amount of 

 copper in solution. The solvent action of carbonic acid as found in 

 rain water and dew is also mentioned. The dew found upon grape 

 foliage which had been sprayed was very carefully absorbed by 

 blotting paper and then analyzed for copper. It was found that 

 when ordinary Bordeaux mixture had been applied, in four cases 

 out of five no copper was found in these tests. When the mixture 

 had been prepared with a small amount of lime some copper was 

 found in every case. But the addition of the chloride of ammonia 

 •caused a large increase in the quantity of copper held in solution. 



In a later paper, :{: the same writer gives an account of otlier 

 experiments from which he draws the following conclusions : 



1. The principal cause of the solution of the copper is the car- 

 bonic acid dissolved in the water which bathes the leaves upon 

 which the Bordeaux mixture has been placed. This explains why the 

 dew that has absorbed this gas acts with great energy as a solvent 

 of tlie copper compounds. 



2. When the leaves treated with the Bordeaux mixture remain 

 for some time in contact with the moist air a large part of the cop- 

 per compounds become gradually soluble. On this account rains 

 may carry away large quantities of the dissolved metal ; and it 

 follows that very frequent rains, although of short duration, dissolve 

 and waste more of the fungicide than do more severe rains which 

 follow each other at longer intervals. 



3. A great excess of lime in the Bordeaux mixture diminishes 

 the amount of copper held in solution in the clear liquid. When 

 such a mixture is applied to foliage the copper is less widely dis- 

 tributed, and can only be found in these places in which solid 

 particles of the mixture have lodged. The lime retards the solvent 

 action of the carbonic acid gas, since before the latter can act upon the 



* Coruell Agrie. Exp. Sta. Bull. 48, p. 291. 



t Sostegni, L'Agricoltura Meridionale, 1891, No. 17, pp. 261-263. 



i Sostegni. Giornale di Viticoltura, Enologia, ed Agraria, 1893, No8. 12 and 13. 



