456 EXPERIMENT STATION RECORD. 



per carboimte tojiother willi sume cui»i»er sulpliulL'. The fungicidal action of 

 the mixture is to be attributed to the copper sulphate. If lime is addetl in 

 quantity just sufficient to precipitate all the copper, and in order to secure this 

 it must be added in the form of limewater, 4CuO,S03 is formed, which by the 

 action of carbon dioxid will reproduce 25 per cent of the copper sulphate taken. 

 If, however, sufficient lime is added to produce a slight allcaline reaction 

 10CuO,8O3 is formed, and the action of carbon dioxid will reproduce only 10 

 per cent of the copper sulphate. When the lime amounts to from 1.2 to H parts 

 of lime for each of copper sulphate the precipitate is cousidered to be a double 

 basic sulphate of copper and calcium. Where equal quantities of lime and 

 copper sulphate are used, as is often recommended, such a proportion would 

 leave a large excess of lime beyond the minimum re(iuiretl. On carbonation 

 this excess, or a greater portion of it, would be attacked by the carbon dioxid 

 before any of the copper compound itself is attacked. In this mixture about 

 10 per cent of the copper sulphate would be reproduced. 



With the more dilute Bordeaux mixture which is made with limewater, the 

 action is more immediate, and as it contains no gritty particles of lime and its 

 efficiency is 2| times that of the ordinary mixture, its use is strongly 

 recommended. 



Various Bordeaux mixtures were made by the author, and carbon dioxid 

 passed through them to determine the liberation of the copper in the mixture. 

 It was found that with the so-called Woburn Bordeaux 25 per cent was lib- 

 erated in 2 hours, with a gradual increase for 2 days, until 40 per cent of the 

 copper was in solution. With the other mixtures smaller quantities were lib- 

 erated, and the efficiency of the Woburn mixture compared with the ordinary 

 Bordeaux mixture is about as 12: 1, or IJ lbs. copper sulphate in 100 gal. water 

 by the Woburn formula is as efficient as 16 lbs. by the ordinary method of 

 manufacture. 



A study was made of dried Bordeaux mixture, the effect of the addition of 

 molasses to Bordeaux mixture, the chemistry of soda Bordeaux, etc. The 

 dried Bordeaux, from the way in which it is made and the chemical changes 

 taking place, is considered a very inefficient spi-aying material. The addition 

 of molasses to Bordeaux mixture, which is advocated by some as making the 

 mixture more adhesive to the leaves, is held to result in the liberation of more 

 copper where iised with the more dilute solution, but with the ordinary Bor- 

 deaux it is not believed to have any particular value. Bordeaux mixture made 

 by the Woburn formula can not be kept in iron vessels, as electrolysis is set up, 

 with the formation of iron oxid. 



The author made an examination into the chemistry of soda Bordeaux mix- 

 ture, and it is said that the reaction requires the addition of 1.84 parts of 

 crystallized carbonate of soda to 1 of sulphate of copper. If either less or 

 more carbonate is used a considerable amount of copper remains in solution. In 

 conclusion the author says that such fungicidal action as soda Bordeaux has 

 is no doubt due to the soluble copper which is present in it for a limited time 

 immediately after its preparation. It can not be regarded as an efficient 

 fungicide, and reports on its action seem to be generally unfavorable. 



The action of lime in excess on copper sulphate solutions, J. ]\I. Bell and 

 W. C. Taber (Jour. PliyH. Chem., 11 (1907), No. 8, pp. 632-636, dgm. 1).— 

 Laboratory experiments were conducted to determine the composition of the 

 solution and of the precipitates obtained when lime and copper sulphate solu- 

 tions were mixed in different proportions and concentrations. Previous investi- 

 gators have held that the composition was very variable, but the authors state 

 that if the materials had been comjiounded at a uniform temperature the 

 solutions would have been found constant in composition. 



