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SOLUBILITY OF THE SCALE OF LEPIDOSAPHES ULMI, LINN. 



By S. Mal'Lik, B.A. (Cautab.), F.E.S., 

 Imperial College of Science and Technology, London, 



The objoc't of this short communication is to state the result of an encjuirv into tlie 

 soUibiHtv of the incrustation of the mussel scale-insect which is destructive to the 

 bark of various cultivated trees, particularly of the apple tree. The control of this 

 pest by means of insecticides to a large extent depends upon getting access to tlie 

 insect by dissolving the scale with which it covers itself soon after it settles down on 

 the bark for the rest of its life. Whatever may be the development of the insect, 

 unless the scale can be dissolved, at least at its point of contact with the bark, no great 

 result can be expected from the application of insecticides. 



Experimental. 



It is generally believed that the incrustation is of a waxy nature. I therefore used 

 the reagents mentioned below to see if a suitable solvent could be found. For these 

 tests the scales were collected from the bark by picking them one by one with a pair 

 of forceps. In this way a sufficient quantity was collected for the purposes of chemical 

 examination. The scales were mechanically separated from the cast skins, etc., bv 

 shaking them in a small tube and then sifting them. By this method a sufficient 

 degree of purity was obtained so as not to vitiate the result of the action of the reagents 

 on the scales. 



Reagents used. 



The following seventeen substances were tested : — Petroleum ether, benzene, 

 alcohol, xylol, chloroform, acetone, toluene, methyl alcohol, carbon bisulphide, 

 methylated ether, carbon tetrachloride, petroleum, terpineol, clove oil, ethyl acetate, 

 pNTidine and soap solution. 



The scales were kept in these reagents for nearly a year, but no action seems to 

 have taken place ; at any rate, the scales were not dissolved. 



Some of the properties of the scale, so far I have been able to tind out, are as follows : 



(1). It is not dissolved by concentrated sulphuric acid. 



(2). It is not dissolved by sodium carbonate, even if heated. 



( 3). It is hygroscopic, losing 8 to 9 per cent, in weight when heated in a water bath. 



(•4). It contains about -I-.j per cent, of nitrogen. The nitrogen content was 

 estimated by the Kjeldahl metliod. 



(5). It dissolves in normal solution of caustic soda or potash. 



Although caustic alkali dissolves the scale in the test-tube, its application a.s a 

 spraying fluid is not quite successful, as has been ascei-tained by me from experiments 

 on trees in the Acton Lodge Orchard. I applied caustic potash solution in various 



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