206 SCIENCE AND FRUIT GROWING 



be preferable to the caustic emulsion. Thus : a 2 per cent, 

 solution of copper sulphate caused no appreciable mortality, 

 even after repeated sprayings, and a I per cent, solution of 

 sulphuric acid proved little better. Turpentine, though fairly 

 effective, was much less so than paraffin. Lead arsenate and 

 sodium arsenate had some slight effect on the eggs. A 10 per 

 cent, milk of lime effected no mortality on one application, 

 though a second application resulted in 20 per cent, of the eggs 

 being killed. No higher percentage than this was obtained with 

 a lime -sulphur-salt wash, or a lime -sulphur-soda wash, whiLt 

 various solutions of sulphides gave still more unsatisfactory 

 results (VI, 99). 



A good deal of attention was devoted to the question whether 

 lime could not be substituted for the caustic soda in the caustic 

 emulsion, and, also, whether the efficacy of a lime-sulphur wash 

 could not be satisfactorily enhanced by the addition of paraffin. 

 Some enhancement, indeed, appeared possible ; but as the manu- 

 facture of such a wash is much more complicated than that of a 

 soda-paraffin wash, there did not appear to be any advantage in 

 adopting it. The substitution of lime for all or part of the soda 

 in the simpler caustic emulsion, resulted in a reduction of 

 efficiency (VIII, 48). 



A 10 per cent, solution of brine or of calcium chloride was 

 found to be fairly effective, killing 30 to 45 per cent, of the eggs 



(VIII, 53). 



Fumigation with hydrocyanic acid was also tried, owing to 

 its having been recommended by the Board of Agriculture for 

 the destruction of mussel scale. It has been used in America for 

 destroying San Jose scale on peach trees, the trees being covered 

 by tents during the fumigation. Such a process is not likely to 

 be adopted in this country at present : but fumigation might be 

 applied to trees before planting, placing them in closed cham- 

 bers. A process which is effectual with San Jose scale, might, 

 however, be quite ineffectual with mussel scale, where the eggs, 

 and not the live insects, have to be killed. To examine this, some 

 pear trees affected by scale were covered over with felted boxes, 

 and fumigated. 1 The scales themselves seemed to have been 

 shrivelled and rendered brittle by the process, but they regained 

 their former condition before long, and the eggs were found to 

 have been uninjured. Very considerable injury, however, was 



1 Using the high proportion of \ oz. of sodium cyanide (equivalent 

 to oz. of potassium cyanide) to every 100 cubic feet in one case, 

 and double this dose in another. With potassium cyanide, 1-3 oz. is 

 equivalent to i oz. of sodium cyanide. 



