110 Journal of Agriculture, Victoria. [10 -Feb., 1919. 



eaaily effloresce, or lose water, on exposure to dry air, so that, even if free 

 from impurities, the water content is far from constant. As explained 

 by Chancrin : — 



" This carbonate may contain 20 per cent., 30 per cent., and even 



40 per cent, of water; freshly prepared, it can contain up to 180 



parts of water for 106 of dry carbonate (63 per cent, water and 



37 per cent, dry carbonate). 



It is even not uncommon to find adulterated commercial carbonate 



containing 20 to 22 per cent, of sodium sulphate, which is incapable 



of neutralizing acidity."* 

 If pure, freshly prepared washing soda, containing 37 per cent, of 

 dry carbonate, be employed, the quantities required to bring about cessa- 

 tion of acidity and commencement of alkalinity — the soda solution being 

 poured into the copper — will be, respectively, 8.6 and 11.5 lbs. for 10 lbs, 

 of copper sulphate. The equivalent quantities of the two substances 

 will perhaps be better understood from the following table (caustic soda 

 has been included, as this substance will be referred to presently) :— 



r^lw^.*^ Pwre Fresh Ciustic 



100% pTity. ^"^'""S ^°''^- ^°'^*'^- 



lbs. lbs. lbs. 



Cessation of acidity .' . .. 3.2 .. 8.6 .. 2.4 



First signs of alkalinity . . . . 4.25 . . 11.5 . . 3.2 



It is thus evident that the quantity of washing soda used according to 

 the 6-8-50 formula is considerably in excess of even the higher figure 

 (first signs of alkalinity) stated above. Instead of 11-^ lbs. for 10 lbs. 

 copper sulphate, 13^ lbs. washing soda would be required. If the washing 

 soda be anything like pure, there would be an excess of soda, entailing 

 undesirable consequences as exj^lained above. If, as is often the case in 

 this dry climate, the washing soda has lost part of its water of crystal- 

 lization, the excess of soda carbonate would be even more considerable. 



If washing soda be used, it would be well to ascertain its content of 

 pure dry carbonate; a simple calculation will then determine the quan- 

 tity to be employed for 10 lbs. bluestone. 



Solvay Soda Carbonate. — This is the form currently used in France 

 for the preparation of copper soda. It is anhydrous, and contains 90 per 

 cent, pure soda carbonate, hence all that is necessary is to employ 11 per 

 cent, more than the quantity stated above for pure anhydrous carbonate. 

 Solvay soda, not being obtainable in the Commonwealth, need only 

 receive passing mention, in order to explain the above quotations, in 

 which its use is referred to. 



Soda Ash. — This substance, which is now obtainable in Melbourne, is 

 really the most convenient and reliable form of soda for use in con- 

 nexion with spray mixtures. Though commercially known as " 58 per 

 cent, heavy soda ash," it is an anhydrous soda carbonate of slightly 

 over 99 per cent, purity. Its purity is thus sufficiently high to enable it 

 to be used in the theoretical quantities stated above. 



Caustic soda may also be employed, but since it contains no car- 

 bonate, the resulting spray would no longer be a Burgundy mixture. 

 Caustic soda is a hydroxide; its composition being very similar to that 

 of quicklime, the reactions taking place would be more similar to those 

 characteristic of Bordeaux mixture than copper soda. Concerning what 



* E. Chunciin—V Uiciillure Moderne (1908), p. 299. 



