10 Oct., 1918.] Copper Fungicides for Vine Diseases. 597 



precipitate thus obtained is much lighter than when concentrated sohi- 

 tions are mixed together. 



By mixing concentrated milk of lime in small quantities at a time 

 into very dilute copper solution practically equal results can be obtained 

 so far as the fineness of precipitate is concerned, but only on the one 

 condition that stirring be very thorough. This has been abundantly 

 proved by experiment. The formula given below is more convenient 

 than the Galloway method, as it does not necessitate the employment of 

 so many vessels to contain the bulky dilute solutions ; with it, only one 

 such is required. Provided that stirring be sufficiently thorough the 

 resultant '' Bordeaux " will be quite equal to that obtained by the Gallo- 

 way method. It also presents the advantage that good results can be 

 obtained with lime not of first class quality. With the Galloway method 

 the lime must be weighed, and with any but quite pure quicklime, weigh- 

 ing is a most unreliable means of ascertaining the true quantity of 

 lime employed. Gauging the lime by means of test paper is in such 

 a case to be preferred. It is, nevertheless, always well to employ the 

 best lime obtainable. Lime which has been partially carbonated gives 

 a " Bordeaux " which may burn the foliage badly. 



Acid V. Alkaline " Bordeaux." 



This is the most important point on which opinions differ. Beams 

 of paper have been written and high authorities may be quoted on both 

 sides in, what may be termed, the battle of green versus blue. Acid 

 " Bordeaux " has a greenish tinge, whereas if it be alkaline the mark- 

 ings left on the leaves of the vine are of a light sky-blue colour. 

 Theoretical considerations concerning the greater efficacy of Tetra- 

 supric sulphate notwithstanding,'" the blue partisans seem to be holding 

 their own in the practical field. Alkaline " Bordeaux " seems to possess 

 greater adherence and to afford at least equal protection in the 

 opinion of some of the leading French authorities to-day. Advocates 

 of acid " Bordeaux " admit the durability of action of the alkaline form, 

 but consider it to be less active when first applied than that which con- 

 tains a considerable amoimt of the slightly soluble Tetracupric sulphate. 

 Into all the details of this interesting controversy it is impossible to go 

 here. It will suffice to say that the conclusion arrived at by Professor 

 Ravaz as the result of extensive field trials carried out during the past 

 two years with numerous different fungicides is that alkaline mixtures 

 have proved themselves quite equal to acid ones. There appears to be 

 remarkably little difference between the practical value of the two. 

 One great advantage of alkaline " Bordeaux " is that it is possible to 

 increase its wetting or spreading power by the addition of casein, a 

 substance which cannot be used in connexion with an acid mixture, 

 by which it would be curdled. 



Wetting Power. 



If a vine leaf be dipped into soapsuds it will on withdrawal be found 

 to be thoroughly wetted, whereas if dipped into pure water large portions 

 of it usually remain dry. Various substances have been recommended 



* Tetracupric sulphate is most abundant in slightly acid " Bordeaux." 



