INSECTICIDES, FUNGICIDES, ETC. 167 



thoroughly dried up, the carbonation of the alkali proceeded 

 much more slowly. Thus, in such a case 13 per cent, of the 

 soda in the wash applied was found to be still in the caustic 

 form after 24 hours, whereas under like conditions with a fresh 

 twig no trace of caustic alkali was found after 12 hours. 



In practical spraying it is improvable that the meteorological 

 conditions would ever be such as to approximate to the prolonged 

 soaking in water applied to these twigs, and the spraying would, 

 doubtless, result in a certain amount of the soda applied being 

 still retained in the wood of the tree; but absorption of it, and 

 subsequent partial liberation on washing, explains one fact which 

 was observed, namely, that a single spraying with the alkali, 

 followed by a spraying with water only, yielded almost as good 

 results as two sprayings with alkali (VI, 106). 



The insecticidal value of an alkaline wash was found to be 

 very conspicuously increased by the presence of paraffin in it; 

 and an account of the results with such a mixture will be found 

 on p. 204. As regards detergent action, however, the addition 

 of paraffin appears to produce little or no increase in effective- 

 ness. The destruction of moss on trees when soda of various 

 strengths was used, without and with the substances mentioned 

 below, was (VI, 147) 



Soda . 

 with Water, with Treacle, with Soap. l ^ nd s^ 



Moss destroyed 46 53 68 74 per cent. 



Thus, the presence of soap, and to a lesser extent, that of 

 treacle, increased the action of the alkali, but only a very small 

 further increase was produced by the presence of paraffin in 

 addition to that of the soap. It was also found that com- 

 paratively strong emulsions containing no soda, as well as 

 undiluted paraffin itself, were without action on moss, unless 

 the paraffin contained a considerable proportion of high-boiling 

 oil ; in other cases, even when the oils contained a moderate 

 proportion of high-boiling constituents, the damage to the moss 

 was only of .a temporary character, the trees soon becoming as 

 green as before. 



The strength of the alkali which had to be applied to ensure 

 the destruction of moss and lichen on trees was found to be 

 about 2 per cent, of caustic soda, or its equivalent (3-2 per cent.) 

 of caustic potash (VI, 143, VIII, 56); in a few cases complete 

 destruction was not affected with this strength, whereas in others 



