27 



Contact Insecticides. 

 Against insects of the second group previously mentioned («'. e., 

 sucking insects) a different means of attaciv must be employed, 

 for, as they do not take in solid nourishment, a poison api)lied on 

 the foliage or stems, as in the case of arsenic compounds, would 

 be of no value. From the nature of their feeding habits they are 

 not as active as the biting insects and often remain fixed in one 

 place for a long time, thus rendering their destruction easy through 

 those insecticides which kill by contact. The general effect of 

 contact insecticides is to suffocate the insects by closing the 

 breathing pores, either by coating them over with a film or induc- 

 ing an irritation which closes them. The most practical and hence 

 most prominent insecticide of this class is kerosene emulsion, the 

 formula for which as given by Professor Fernald is presented 

 herewith. 



Kerosene Emulsion. 



"This most useful insecticide is prepared in the following 

 manner : One-quarter of a pound of common bar soap is dissolved 

 in two quarts of boiling water, and while still hot four quarts of 

 kerosene oil are added and the whole mixture churned through a 

 small hand force-pump with the small nozzle turned into the pail. 

 This churning must be continued about five minutes, until the 

 whole forms a creamy white mass which becomes jelly-like when 

 cool. Care must be taken to have the soap solution hot when the 

 kerosene is added to it and the churning done, but it must not be 

 near a fire. 



" Before applying the emulsion to plants it should be diluted 

 "with water in the proportion of one quart of the emulsion to nine 

 quarts of water, which must be thoroughly mixed. The above 

 will make sixty quarts of insecticide ready for use, but the emul- 

 sion will keep for a long time without injury and may be diluted 

 at the time of using. This insecticide is said to be one of the best 

 substances for the destruction of vermin on domestic animals and 

 in hen houses." 



The dissolving of the soap requires considerable time, and I find 

 that the emulsion may be prepared more expeditiously and equally 

 as effectively by use of the same or a little greater quantity of any 

 good soap powder in place of the bar soap. The common soap 

 powders readily dissolve in hot water, thus obviating the necessity 

 of cooking the mixture over a stove, and so far as I have observed 

 make an excellent emulsion. Samples prepared four weeks ago 

 are as permanent as when made, and I see no reason why they 



