534 



JOUKNAL OF THE EOYAL HOliTlU ULTUEAL SOCIETY. 



on the nature of emulsions has led to the conclusion that emulsification 

 of oil in water depends on the presence of minute solid particles which 

 arrange themselves round the oil globules, enclosing them in a sort of 

 skin and thus preventing them from coming into contact with each other 

 and coalescing. In the case of soap, so commonly used as an emulsifying 

 agent, the solid particles are formed locally and temporarily in the neigh- 

 bourhood of the oil gobules, owing to the soap being insoluble in the oil. 

 The want of actual insolubility in such cases accounts for the frequent 

 occurrence of spontaneous de-emulsification, which forms a drawback to 

 the use of soap as an emulsifier. This apparently never occurs when the 

 emulsifier is permanently insoluble. Various substances precipitated from 

 solutions have been found to act as emulsifiers, among the best being 

 basic sulphates of copper and iron. It is only necessary to add a little 

 lime to a solution of sulphate of copper or sulphate of iron to obtain a 

 precipitate of the basic sulphates, and when paraffin is churned up with 

 these it immediately forms a bulky and fine-grained emulsion, which is 

 quite permanent, and perfect for spraying purposes. A great advantage 

 of the use of such emulsifiers is that various substances may be mixed 

 with the emulsion, notably caustic soda, without producing de-emulsifica- 

 tion, thus removing the one serious drawback to the Woburn wash. 

 When sulphate of copper is used as the emulsifier the wash will have 

 fungicidal properties, and will, as a matter of fact, contain Bordeaux 

 mixture ; but if no such properties are required the cheaper sulphate of 

 iron may be used. Emulsification with thes y e basic sulphates is much 

 more satisfactory when the paraffin is a high-boiling oil, such as solar 

 distillate, which is half the price of burning oil and can be sent by rail 

 without being charged as an explosive. Directions are given for the 

 making of caustic winter washes with copper and iron sulphates, and a 

 summer wash (without caustic soda), as instances of the way in which 

 paraffin can be emulsified with almost any insecticide or fungicide by 

 making use of precipitated solids as emulsifiers. The chemical student 

 will find in the appendix to this report papers by Mr. Pickering on 

 the " Interaction of Metallic Sulphates and Caustic Alkalies" and 

 "Emulsions."— A. P. 



EntomophagTOUS Parasites. By (a) C. Arranger, (b) Q, Doublesel 

 (Le Jard.. vol. xxiii. No. 540, p. 245 ; August 20, 1909 ; 5 figs.)— A plea 

 for the protection and encouragement of the larvae which prey upon 

 various caterpillars, as already indicated on the note by the same author 

 on Tachinae. The article is well worth the consideration of horticul- 

 turists.—^ 7 . A. W. 



Erlangea tomentosa. By J. Hutchinson (Bot. Mag. tab. 8269).— 



Nat. ord. Compositae ; tribe Vemonieae. Trop. E. Africa. Shrub, 5 feet 

 high ; leaves oblong, 2-5 inches long, doubly serrate, pubescent above, 

 villous- tomentose below ; heads lilac, on a branching panicle, 6 inches 



across. — G. H. 



Euphorbia Ledienii. By N. E. Brown {Bot. Mag. tab. 8275).— Nat. 



ord. Euphorbiaceae ; tribe Euphorbieae. S. Africa. Shrub, succulent, 



