96 xMASS. EXPERIMENT STATION BULLETIN 252 



organic acids such as citric, gallic, glyceric, lactic, malic, saccharic, sali- 

 cylic and tannic acids, in the presence of alkalies, form soluble cupri 

 compounds with a small amount of basic salt in some instances. The 

 structural formulae of the cupri compounds lack confirmation. Organic 

 acids that do not contain alcoholic hydroxyls form insoluble basic salts 

 under the same conditions. 



In tests made at this laboratory with Bordeaux 4-2-50, soluble copper 

 was observed with 0.048 per cent gallic, 0.048 per cent pyrogallic and 

 0.080 per cent tannic acids but probably occurred in lower concentra- 

 tions. Although hydroxy-organic acids produce soluble copper with Bor- 

 deaux and Burgundy mixtures, and are less likely to yield cuprous oxide, 

 there is very little information available relative to their practical use in 

 this connection. The soluble copper produced by the action of sugars 

 and of hydroxy acids in the i^resence of alkalies is presTimably a true 

 solution. 



(c) Albuminous substances containing two amino (NH-) groups linked 

 to different carbon atoms, so-called biuret conipounds, also produce solu- 

 ble copper in the presence of alkalies. Of the more conmion substances 

 may be mentioned gelatine, glue, casein, albumen, milk and calcium casein- 

 ate, although they are seldom employed for this purpose. 



In tests with Bordeaux 4-2-50 in the station laboratory, soluble copper 

 was observed with 0.048 per cent glue and 0.160 per cent casein^; and in 

 the case of Bordeaux 4-4-50 with 0.05 per cent gelatine, and 0.05 per 

 cent glue; and traces with 0.10 per cent casein and 0.10 per cent albumen on 

 standing 24 hours. In additional tests with Bordeaux 4-4-50 and 0.10 per 

 cent protector, a trace of soluble copper was observed with albumen, in- 

 creasing with casein and glue to an appreciable amount with gelatine which 

 gave a purple solution. The soluble copper produced by biuret compounds 

 seems to be colloidal as it did not pass a collodian sack and apparently 

 exhibited Brownian movement (Gilligan), but requires further investiga- 

 tion. 



All the soluble organic copper compounds mentioned are evidently less 

 active and less toxic to foliage than like amounts of soluble copper in 

 inorganic combination and yet may prove of service in some instances. 

 The supplements may also increase wetting and spreading and possible 

 adhesiveness in the case of some proteids. 



2. To increase suspension by deflocculating the fungicide, by increasing 

 the viscosity of the dispersion medium, or both. 



The suspension of copper fungicides depends largely on the degree of 

 dispersion and the character of the particles, as added substances seldom 

 have a noticeable deflocculating action but merely retard subsequent ag- 

 glomeration and increase the viscosity of the dispersion medium. Light 

 amorphous products naturally have a higher power of suspension tlian 

 those of a dense, crystalline character. 



Several references have been noted. Kelhofer (49) claims that sugar 

 increases the suspension of Bordeaux; Neuweiler (65) that 0.01 to 0.20 

 per cent of tannin is effective; and Winston, Bowman and Yothers (97) 

 that 1 per cent of oil emulsion with Bordeaux 3-3-50 settles less rapidly. 



An effort was made to determine the eft'ect of numerous substances on 



'Dissolved in sodium hydroxide ia this instance. 



