220 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
example of such may be found in an emulsion where soft soap is 
present only to the extent of J per cent, and the paraffin to the extent 
of 5 per cent. Such an emulsion is almost bound to scorch, and 
should be discarded. 
The second class, or risky emulsions, consists of those which, 
although reasonably stable when kept unagitated in a vessel, are liable 
to partial de-emulsification when sprayed forcibly on to a plant. In 
this class the amount of soap is so reduced that, though in a quiescent 
state it is sufficient to prevent the paraffin globules uniting with 
each other, yet, when subjected to mechanical shocks as in the act of 
spraying, it is not sufficient, and a certain amount of free paraffin is 
received by the plants sprayed. An emulsion containing i per cent, 
of soap and 2 per cent, of paraffin is an example of this class. Such 
emulsions should not be used in practice, and indeed their use is not 
necessary, as full wetting power may be obtained by the safe formulae. 
The third class is stable even when sprayed. A higher proportion 
of soap is present and a lower one of paraffin than in many spray- 
fluids commonly advocated. The most satisfactory of this class, 
regarded from the point of view of great wetting power and absence 
of scorching, is found in the formula 2 per cent, soap, 2 per cent, 
paraffin. This mixture is capable of wetting woolly aphis of apples 
or the conidial stage of American gooseberry mildew. 
Besides soap and paraffin emulsion there are certain other sub- 
stances that have been advocated for their wetting powers, such 
as saponin, casein, and gelatine. Saponin is rather an expensive 
substance, but casein and gelatine are used in such small quantities 
that their cost is negligible. Casein is suitable for alkaline solutions, 
and gelatine for neutral or acid ones. The strengths advised vary 
between one in a thousand and one in ten thousand. In the following 
table the wetting power of casein, gelatine, soft soap, and paraffin 
emulsions are compared. 
Comparative Wetting Power of Various Substances. 
Surface 
Gooseberry Leaf 
Sea-kale Leaf 
American Gooseberry 
Mildew 
Substance 
Water . 
Gelatine, i in 1,000 . 
i in 10,000 . 
Casein, 1 in 1000 
„ 1 in 10,000 . 
\ Soft Soap \% . 
>) >j 1 % • 
; „ 2%. 
Paraffin Emulsion 
1 %, 1 % 
>> >> I i%> 
„ 2 %, 2 % 
>> >> 1 %> 5 % 
„ 2 %, 1 % 
Nearly complete 
Complete 
>> 
>> 
>) 
?> 
>) 
» 
>> 
> ? 
None 
Very slight 
> > 
Slight 
Nearly complete 
>> 
)> 
Complete 
Wets by oil, 
not by water 
Complete 
None 
>> 
> > 
;> 
>) 
Very slight 
>> 
Moderate 
Nearty complete 
Complete 
Wets by oil, 
not by water 
Moderate 
