23 



SOAPS. 



The value of fish-oil soai)s as insecticides lias been particularly em 

 phasized during the past year as a result of experiments (tonducted by 

 the division against the San Jose scale. A full statement of the out- 

 come of these experiments is given in an article in the last number 

 of Insect Life (vol. vii, pp. 365-374) A full discussion is there given of 

 the effect of the soap on the trees at various strengths, and of- the 

 nature and results of its acti(m on the scales. The action of soap 

 washes on insects has also been carefully investigated recently by 

 Targioni-Tozzetti, and Del uuercio. The experiments of these gentle- 

 men have been more particularly in the examiimtion of the physio- 

 logical action of the soap on insects. The conclusion reached, which 

 seems to be i^retty well sustained by the experiments, is that soap has 

 the same action that lias been assigned to oil, asphyxiating the insects 

 by closing the stomates, and that the effect is therefore mechanical and 

 not due to any particular caustic action. They made microscopical 

 examinations of insects and found that the soap solutions were effec- 

 tive in forming a delicate film over the external opening of the trachea. 

 The}^ also found the various emulsions experimented with to be effec- 

 tive in proportion to the amount of soap contained in them. Their 

 emulsions, however, were not of the kind we should consider satisfac- 

 tory. They conclude that simple soap solutions are quite as effective 

 as the more complex emulsions, and seem disposed to abandon emul- 

 sions in favor of soap. This is probably going further than the facts 

 warrant, particularly as a careful examination of the writings and 

 experiments of these gentlemen shows that they have not succeeded in 

 making a satisfactory kerosene emulsion according to our standard; 

 but it emphasizes the growing tendency to place soaps among the more 

 valuable insecticides. 



In this connection it may be well to call attention to an error which 

 seems to have become Avidespread, relating to the domestic or home 

 manufacture of soaps. -A formula is frequently given nowadays which 

 makes the astounding statement that some 20 pounds of good soap can 

 be obtained by combining 1 pound of lye with 3 pounds of fish oil in 

 3 gallons of water. This formula had its origin in some experiments 

 conducted by Mr. Alwood in the work of the division on remedies for 

 the hop aphis, llecent careful exi)erimentation in soap manufacture, 

 repeated many times, has shown that there is no possible ground for 

 this statement, and on consultation with three or four prominent soap 

 manufacturers the absurdity of the statement was at once apparent. 

 The fact is that a good hard soap, such as the ordinary whale-oil soap, 

 very little exceeds in weight the combined weights of the oil and lye 

 or grease, and not more than one-fourth or one third increase in weight 

 can be reasonably counted on. lleiu'e tor the proportions given above 

 J or 5 ixmnds of hard soap is the limit. It is true that almost any 



