INSECTICIDES, FUNGICIDES, ETC. 165 



form) was, is uncertain. It probably was the outcome of a 

 belief that two things are always better than one, which doubt- 

 less may have met with apparent support in this case by some 

 chance results obtained on certain occasions (pp. 200, 208), but it 

 is evident, if merely from the proportions recommended, that the 

 recommendation is without theoretical or practical basis; for, 

 so far as alkalinity is concerned, one part of caustic potash is 

 by no means equivalent to one part of caustic soda, and there 

 is no reason why equal weights of them should be used : .the pro- 

 portions required for equivalence (making allowance for the fact 

 that commercial potash contains only 87 per cent, of the alkali) 

 being 1*6 parts of the former to i part of the latter. The relative 

 quantities of these, and also of potassium carbonate, required 

 to produce the same alkalinity, and the cost of them at pre-war 

 prices, are as follows 



Caustic soda, i Ib. . . . . . costs qd. 



Caustic potash, 1-6 Ib. . . ,. ,, I2%d. 



Carbonate of potash, 3-8 Ib. . . . 



The substitution, therefore, of the potassium compounds in any 

 form for their equivalent of caustic soda is economically unsound. 



It has been suggested that such a substitution has its advantage 

 in that the potash which reaches the ground possesses a manurial 

 value. If that were the reason for using it, it would be better 

 to use nothing but potash, or better still to apply the potash 

 to the soil in some cheaper form, and use the soda on the trees. 



That there was no intrinsic difference in the action of caustic 

 soda and caustic potash was established by examining the action 

 of each of them on mussel scale (p. 201). Taking the caustic 

 alkali in equivalent proportions (i of soda or 1-6 of potash) 

 there were 35 cases for comparison : in 16 of these the action 

 on the eggs was the same with either alkali, whilst in 9 it was in 

 favour of soda, and in 10 in favour of potash ; or, omitting some 

 uncertain results, out of 31 cases, 8 were in favour of soda, and 

 7 in favour of potash. Evidently a case of equality of effect. 



In contrasting the effect of a mixture of the alkali with that 

 of either soda or potash by itself, the alkalinity being the same, 

 10 series of experiments were made : in 4 of these there was 

 no difference between the results, in 5 cases the values were 

 very slightly in favour of a mixture, whereas in the remaining 

 case they were strongly in favour of a single alkali ; evidently, 

 again, a case of practical equality of action. 



No experiments were made with potassium carbonate by itself, 



