COPPER AND ITS SALTS. 237 



of crystallised copper sulphate) per litre of must was found to 

 retard the commencement of fermentation. On the other hand, 

 P. Prom (I.) stated in 1891 that the addition of less than 150 

 mgrms. of copper per litre of must had no adverse influence on 

 the development and fermentative action of the species of wine 

 yeast examined by him. Both workers, however, omitted to bear 

 in mind Polacci's observation that the copper sulphate added to 

 wine must combines with the tartrate present to form potassium 

 sulphate and copper tartrate, which latter, being insoluble, is 

 precipitated and thrown out of action. Observing this precaution, 

 F. KRUGER (I.) in 1894 found, in the case of a pure culture 

 Johannisberg yeast, that the maximum amount of copper sul- 

 phate present in solution and therefore active that the yeast 

 would stand without appreciable injury was equivalent to 44-45 

 mgrms. of copper per litre. When increased above this limit it 

 gradually diminished the fermentative power, though the repro- 

 ductive faculty and fermentative capacity were not so quickly 

 destroyed. In the experiments conducted on low-fermentation 

 beer yeasts by H. WILL (I.), a large number of cells, after immer- 

 sion in a 5 per cent, solution of copper sulphate for twenty-four 

 hours still proved capable of fermenting the sugar solution to 

 which they were transferred. 



The assumption that the above figures obtained by Kriiger 

 may be of general application was controverted by the important 

 discovery, made by E. BIERNACKI (I.) in 1891, to the effect that 

 the amount of antiseptic (here copper sulphate) necessary to 

 retard the fermentative activity of yeast varies with the amount 

 of the sowing. This has been confirmed by other workers ; for 

 example, by H. MANN (I.), H. POTTEVIN (I.) and A. AMAND (I.) in 

 connection with copper sulphate ; by Mann in the case of iron 

 sulphate, lead acetate and corrosive sublimate; by 0. WEHMER 

 (XY.) with potassium and sodium arsenite, and by MULLER- 

 THURGAU (XVII.) in the case of sulphurous acid. Nevertheless, 

 though the idea of obtaining unconditionally accurate limit values 

 in this way must be abandoned, it is still highly desirable to make 

 further investigations, especially on the comparative sensitiveness 

 of different pure yeasts and more particularly as a contribution to 

 the solution of the important question of the influence of the 

 copper treatment on the modification of the yeast flora of the 

 vine. 



It should be mentioned as might be foreseen from particulars 

 already given in vol. i. p. 118, when copper sulphate is added in 

 far smaller quantities than the above limits, it no longer restricts, 

 but actually stimulates the fermentative activity of yeast. This 

 occurs, according to Biernacki, when the dilution' reaches the pro- 

 portion of i part of copper sulphate per 600,000 parts of nutrient 

 solution. 



Apart from very exceptional cases, the vintager has no need to 



