10 Feb., 1919.] Copper Fungicides for Vine Diseases. Ill 



we may term " copper caustic soda " spray mixture, Professor Eavaz 

 writes recently as follows, in answer to a correspondent : — * 



" It would seem that ' copper caustic soda ' should be as effica- 

 cious as spray mixtures made with lime or soda carbonate. When 

 prepared in the usual manner, i.e., dilute soda into copper sulphate 

 solution, on reaching neutrality, a fine blue mixture results, which 

 recalls Bordeaux mixture. The precipitate is different. It consists 

 of copper hydrate, not in vesicular form, but presenting the aspect 

 of a fine-grained gelatinous mass, similar to copper soda precipitate. 

 It is therefore highly probable that such a mixture should give very 

 satisfactory results. 



As regards foliage damage, this seems to be nil, or almost nil. 

 Vines treated with this mixture remain intact, whilst control plots 

 treated with copper soda showed the usual amount of scalding. 



This applies to a neutral mixture. . . . It is to be feared 

 that distinctly alkaline mixtures would not be free from risk to 

 vegetation on account of the free caustic soda present. . . . 

 Trials may be made with such a mixture, but trials only.'' 

 Professor Ravaz significantly concludes : — 



" It is always imprudent to risk one's crop in connexion with a 

 novelty." 

 The equivalence of caustic soda and pure soda carbonate is shown in 

 the table on page 110. According to this, 3 lbs. should be the proper 

 quantity for 10 lbs. of bluestone. To be on the safe side, it would be 

 well to check the reaction with phenolphthalein paper, adding a small 

 quantity of bluestone solution, previously withdravna, after neutraliza- 

 tion has been effected, as has been explained in connexion with 

 Bordeaux mixture. 



Practical Directions. 



The following method of preparing copper soda is based on the 

 researches of Professor Fonzes-Diacon ; it is the one which will probably 

 be found most satisfactory. It is as follows, for 50 gallons of spray 

 mixture : — 



A. Dissolve 10 lbs. bluestone in 20 gallons of water, place this in the 

 60-gallon hogshead, with one head removed, in which the mixture is 

 to be made. JSTeedless to remark, a stock solution of bluestone, such as 

 was recommended in connexion with Bordeaux, will be found very 

 convenient. 



B. Dissolve 3^ lbs. of soda ash in 30 gallons of water ; pour the soda 

 solution into the copper in a thin stream, with very thorough stirring. 



C. If washing soda be used instead of soda ash, and this be pure and 

 fresh (37 per cent, purity), the quantity required would be 9 lbs. Dis- 

 solve this in 30 gallons of water, and mix as described in the prsceding 

 paragraph. 



The resulting 50 gallons of spray mixture should be applied imme- 

 diately. It must not be kept from one day to the next. 



It will be observed that the quantities above mentioned are not in 

 absolute agreement with the figures mentioned in connexion with the 



* Progres Agricole, 7th April, 1918, p. 315. 



