264 ANNUAL REPORT OF THE Off. Doc. 



some others have done equally well; but ou the other hand, some have 

 obtained bad results only. It seems to be very largely a matter of 

 locality and climatic conditions. The same experimenter has spray- 

 ed peach trees safely with undiluted kerosene in one section of his 

 State, and killed every treated tree in another. Therefore undiluted 

 kerosene should be cautiously and experimentally used, especially 

 on peach, until its local effect is determined. The precautions to be 

 observed are: Spray with a very fine nozzle; use no more than 

 enough; see that the trees are dry and that the weather is such as to 

 favor rapid evaporation. 



The cost of kerosene varies from six to ten cents per gallon accord- 

 ing to locality. It is therefore about as expensive as whale oil soap 

 of equal quantity; but kerosene is so much more penetrating and 

 spreads so much better, that a given quantity will cover almost twice 

 as much surface as the same quantity of soap suds. 



Kerosene depends for its effectiveness upon its penetrating power 

 which carries it through and under the scale, into contact with the 

 insect below. 



CRUDE PETROLEUM. 



Crude petroleum is the natural product as it is obtained from the 

 oil wells, and varies greatly in composition. I need not go into de- 

 tails ou this point further than to say, that to be useful for insecticide 

 purposes it should have a paraffine base and, if used undiluted, should 

 have a specific gravity of forty-three degrees or over on the Beaume 

 scale. I do not mean to assert that oils with an asphaltum base may 

 not be useful ; but I know nothing about them as insecticides. There- 

 fore, whenever crude oil, or crude petroleum is mentioned in this Bul- 

 letin it must be understood as a parafiine base oil of forty-three de- 

 grees or greater specific gravity. Such oil is produced in Pennsyl- 

 vania, West Virginia and Ohio, and it may be either green or amber 

 in color. 



Crude oil contains the light napthas, the somewhat heavier illumi- 

 nating oils, and, in addition, a variable (juantity of paraffine and vase- 

 line. When it is sprayed on a smooth surface so as to make a thin 

 covering, the light oils evaporate in a very short time, leaving a film 

 of greasy material which is the vaseline and paraffine. If the surface 

 be non-absorbent this film will remain indefinitely through heat and 

 cold, provided dust be excluded. In the heat it will thin out a little; 



