INSECTICIDES, FUNGICIDES, ETC. 177 



be about twelve times (or possibly eighteen times) more effective 

 as a fungicide than ordinary Bordeaux mixture ; or, that to get 

 the same effect, it would be necessary to use only one-twelfth 

 as much copper. 



For making the individual basic sulphates it is necessary to 

 use clear lime-water, so as to avoid excess of lime, and a fungicide 

 prepared in this way had, in fact, been in use in parts of Italy 

 for some time. It was found, however, that the basic sulphate 

 A, which would be the most economical as regards the proportion 

 of copper sulphate liberated by the action of air, was of too dense 

 a nature to constitute a satisfactory spraying material, and that 

 it was preferable to use the more highly basic compound, C, 

 (ioCuO,SO 3 ), at some sacrifice in economy. The relative 

 volumes occupied by the various compounds, after being allowed 

 to settle for the same times, were found to be as follows 



A. ioCuO,2-5SO 3 .... 8 



B. ioCuO,2SO 3 17 



C. ioCuO,SO 3 . . . .86 



D. ioCuO,SO 3 ,3CaO . . . .98 

 F. ioCuO,3oCaO . . . . .5 



A mixture of the sulphates B and C has been put on the 

 market under the name of Bordeaux paste or Bordorite. It 

 consists of the precipitates obtained by the action of lime-water 

 on copper sulphate, with the excess of water drained off, so as 

 to leave the product in the form of a paste of convenient con- 

 sistency, to which it is only necessary to add water to reproduce 

 the original precipitates in the same condition as they were 

 when first precipitated : l such a spray-fluid also presents the 

 advantage over ordinary Bordeaux mixture, of containing no gross 

 particles of lime to clog and wear the nozzles of the spraying 

 machine. 



It must be borne in mind, however, that this paste is a substitute 

 for ordinary Bordeaux mixture, and does not reproduce the 

 ordinary mixture when diluted with water; it could not do so, 



1 G. H. Pethybridge (Journ. of Irish Board of Agric., XV, 498) states 

 that the paste is " colloidal " when first prepared, but changes from this 

 condition after being kept for no very long period. But he is evidently 

 under some misapprehension as to the meaning of the term colloidal, 

 which cannot be applied to any of the basic sulphates, and some explana- 

 tion is required as to the condition they are supposed to be in when they 

 lose these " colloidal " properties. As a matter of fact, these precipitates 

 remain quite unchanged in physical properties for an indefinite time, 

 so long, of course, as they are not decomposed by chemical agency, or 

 deprived of their combined water by drying, or freezing (see p. 227). 

 N 



