108 Jourtial of Afiricvlturr, Victoria. | 10 Fkb., 1010. 



precipitate in varying quantities once the proportion of soda exceeds 

 3.2 lbs. for 10 lbs. copper sul]>hiite. Even with the mininiuni of soda 

 required for neutrality the precipitate will not consist entirely of basic 

 sulphate. There will always be a certain proportion of copper hydro- 

 carbonate formed. 



The respective strengths of the solutions of copper sulphate and soda 

 carbonate influence to a considerable extent the nature of the precipitate. 

 Let us consider the smaller quantity of soda, viz., 3.2 lbs. for 10 lbs. 

 copper sulphate. If each of these be dissolved in 25 gallons of water, 

 and the soda solution carefully stirred into that of copper, the precipitate 

 formed will consist of about 60 per cent, of tetracupric sulphate. 



If the copper sulphate be dissolved in 45 gallons of water, and the 

 soda in 5 gallons, and the latter slowly stirred into the first, the precipi- 

 tate will only contain 50 per cent, of basic sulphate. 



If, on the other hand, the copper sulphate be dissolved in 5 gallons of 

 water, and the soda carbonate in 45 gallons, the latter solution being 

 slowly stirred into the former, the precipitate will consist of 75 per cent. 

 of tetracupric sulphate. 



Though the bulk of the copper is contained in the precipitate, irre- 

 spective of the procedure followed, the supernatant liquid also contains 

 copper in solution. If the proportion of soda to copper sulphate be 3.2 

 to 10, or under, this dissolved copper will be mainly present in the form 

 of tetracupric sulphate in carbonic solution ; it may amount to the 

 equivalent of 100 grms. of crystallized copper sulphate per hectolitre of 

 1 kilog. mixture fO.l per cent.). On spraying, the carbonic acid 

 evaporates, leaving the basic sulphate on the tissues of the vine. 



If the proportion of soda carbonate be increased to 4.257 lbs. for 

 10 lbs. of copper sulphate, a curious difference in the composition of the 

 supernatant liquid will be found, according to the manner of mixing, 

 whether this be wholesale and sudden or slow and gradual, though in 

 both cases soda be poured into copper. In the first case, the carbonic 

 acid gas which is suddenly liberated dissolves some of the copper hydro- 

 carbonate. In the second, the carbonic acid is almost entirely liberated 

 during mixing, and the supernatant liquid Avill contain but little bi- 

 carbonate of copper in solution. 



Sufficient has been said to show how complex the chemistry of copper 

 soda really is. Space will not permit of dealing with the intricate question 

 of the copper carbonates. Those interested will find full information on 

 the subject in the paper by Spencer U. Pickering, which appears in the 

 Transactions of the Chemical Society, 1909, and which is reproduced as 

 an appendix to the 11th report of the Woburn Experimental Fruit 

 Farm. 



Acid, Neutral or Alkaline. 



Like Bordeaux, copper soda may present either of the above reactions. 

 Always taking 10 lbs. of bluestone for 50 gallons of mixture (the 2 per 

 cent, spray), and pouring soda solution into copper, it will be acid with 

 less than 3.2 lbs. of pure anhydrous soda carbonate. It will be neutral 

 if the quantity of soda be between the limits of 3.2 lbs. and 4.25 lbs. If 

 more than 4.25 lbs, pure soda be used, it will be alkaline. 



Acid copper soda consists mainly of tetracupric sulphate, Avith a 

 slight quantity of free copper sulphate in solution. If neutral, it con- 

 sists of a mixture of tetracupric sulphate and copper carbonate; the 



