178 MANUAL OF MODERN VITICULTURE. 



were very satifactory. Ultimate researches enabled experi- 

 menters to ascertain that the active substance in this mixture 

 was the copper, and that traces of compounds of this metal 

 in water were sufficient to prevent the germination of Plas- 

 mopara conidia. Different cupric compounds adhering to 

 the leaves were therefore tried, with the object of forming a 

 deposit which would furnish the drops of water resulting 

 from dew or fogs (and in which the spores of the disease 

 germinate), with traces of copper. The principal matters- 

 recommended were : 



A. Liquid matters 



1. Bordeaux mixture. 



2. Blue water. 



3. Copper ammoniacal solution. 



4. Mixture of Dauphinee. 



5. Verdet gris. 



6. Copper sucrate. 



B. Pulverized solid matters 



1 . Mixture of sulphur and sulphate of copper. 



2. Sulpho-steatite. 



3. Skawinski powder and sulphur. 



(a). Liquid Matters. 



1st. Bordeaux mixture. This is a mixture of quick lime 

 and sulphate of copper. If freshly-slacked lime is poured 

 into a solution of sulphate of copper a light blue precipitate 

 is obtained, remaining a certain time in suspension in the 

 liquid, which is a hydrated oxide of copper surrounded with 

 a little sulphate of lime and free lime, the latter soon 

 becomes carbonate of lime. Under this form copper adheres 

 strongly to the parts of the plant upon which it is applied, 

 and dissolves in small quantities in rain water or dew con- 

 taining carbonate of 'ammonia or carbonic acid. 



The Bordeaux mixture is prepared in the following 

 manner : 6 Ibs. of sulphate of copper is added to a gallon 

 of warm water ; after the crystals have dissolved the solution 

 is poured into about 100 gallons of water ; on the other hand, 

 4 Ibs. of freshly-slacked lime (milk of lime) are added to 

 2 gallons of water, and the milk of lime thus obtained slowly 

 poured into the copper solution, stirring the whole time so as 

 to mix it thoroughly and assist combination. The mixture 

 should be prepared in a wooden vessel on account of the 



