134 First Report on Economic Zoology. 
Three or four broods may occur in tropical climates. It is known 
under a variety of popular names, such as the Purple Scale and the 
Orange Mussel Scale. 
Treatment of Affected Trees. 
There are two ways of treating scale-insect attack : — 
I. Spraying, with either paraffin emulsion or resin wash. 
II. The gas treatment. 
1. Spraying for scale attack. 
A. Paraffin emulsion. This is used to kill the larval scale 
insects when they are crawling from beneath the scales and to 
corrode the scales away. The time of migration of the larvae should 
be noticed when this wash is used, and the wash applied when they 
are crawling about, to do most good. But it has been found more or 
less satisfactory at any time if applied on several occasions during 
the year, best at intervals of two weeks. 
Paraffin emulsion is made as follows : — Mix equal portions of 
soft soap dissolved in boiling water and paraffin, and then churn 
them up by means of a force pump until a creamy emulsion is 
produced. When required for use mix with twenty times its bulk 
of water. 
B. Resin wash. There are many recipes for this — the following 
is a good one : — dissolve 1 lb. of caustic soda in 1 J gallons of soft 
water, then dissolve 2 lbs. of resin and 1 lb. of tallow by moderate 
heat, and as it is cooking stir in gradually 1 quart of the dissolved 
caustic soda solution, and then add water until you have 22 pints of 
liquid. This forms a thick brown soap which is sufficient for 44 
gallons of wash ; it being added to the water and well stirred ; warm 
water, if possible, should be employed. This should be applied before 
the blossom bursts, but in bad attacks it may be used later as 
it is well to clear out the scale, even at the loss of all that year’s 
crop, through destroying the blossom. 
2. Gas treatment. This is largely employed for scale in the 
United States, the Cape of Good Hope, etc. The trees have to be 
covered with a tent of gas-proof canvas ; the hydrocyanic acid gas is 
generated by putting water and sulphuric acid in a saucer or jar 
and then putting lumps of 60 per cent, grade cyanide of potassium 
into the mixture. The fumes may be allowed to ascend for an 
hour or more — evening or dull days are the best times to fumigate. 
The slower the gas generates the better ; the greater the quantity of 
