EXPERIMENT STATION BULLETINS. 487 



Mansierf who first suggested counting the drops in equal volumes of 

 liquids under proper conditions of temperature, etc., for making a study 

 of their surface tension in connection with insecticides. It was found 

 that gelatine, glue, soluble albumen, and saponin could all be used in 

 lime-surphur to increase the "spread" on the bark of a tree. The vari- 

 ous agents were dissolved in the proper amount of warm water, after 

 which the solution was added to concentrated lime-sulphur in making up 

 the proper dilution. Glue and gelatine had to be used at the rate of 

 about one pound to eleven gallons of lime-sulphur wash as diluted ready 

 for use. The expense, therefore, would be too great to make their em- 

 ployment practical. This was true also in the case of albumen and 

 saponin. Except for its expense, however, saponin seemed to be best of 

 all the agents tried for the purpose. It dissolved readily, and a com- 

 paratively small amount added to the lime-sulphur increased the 

 "spread" to the desired point without any apparent injury to the oxygen- 

 absorbing power of the wash. Tests were made of this last point in the 

 following manner: 



A measured amount of the solution of saponin in water was added to 

 a measured amount of concentrated lime-sulphur in a stender dish of 

 standard volume and diameter; then, an equal sample of the same con- 

 centrated lime-sulphur, in a dish of the same diameter, was diluted with 

 a volume of distilled water equal to the saponin solution used. The two 

 dishes were introduced into exactly similar containers with equal vol- 

 umes of air having the same known percentage of oxygen. At the end of 

 a certain period of time (G hours, for example) the oxygen percentage 

 in each air-chamber was again determined, and from that, the volume 

 of ox3'gen that had been absorbed. The volumes of oxj'gen absorbed in 

 the saponiu-lime-sulphur and in the check were practically the same — 

 the greatest difference in three successive tests being no greater than 

 the possible experimental error of the apparatus. AVhen the dry pow- 

 der was stirred directly into the lime-sulphur, however, the oxygen-ab- 

 sorbing ability of the solution was quite appreciably weakened. This 

 was due no doubt to oxidation of the sulphides by air carried in with the 

 dry powder. It was best, therefore, to dissolve the saponin in water, 

 and then add that solution to the concentrated lime-sulphur. 



Four tests were carried out to determine the influence of adding sapon- 

 in, upon the rate at which water Avould evaporate from lime-sulphur (i. 

 e. influence upon rate of drying). In every case, the evaporation was 

 found to be a little more rapid from the lime-sulphur to which saponin 

 had been added — as might be expected from the weakened surface ten- 

 sion. The ditt'erence, however, was not great — amounting to only 0.1 

 grm. of water from an area of 10.17 cm. in seven hours, on the average. 

 This difference could be largely eliminated by adding salt (Na CI) to 

 the saponin-lime-sulphur solution. That is, salt had the effect of retard- 

 ing the evaporation of water. It was used at about the rate first recom- 

 mended in the original lime-sulphur salt-wash (i. e. about 18 lbs. to 

 100 gallons). Except in extremely diy weather or in a normally dry 

 climate the salt would not serve a useful purpose. 



Finally, all the tests tried seemed to confirm the first impression that 

 saponin would be the ideal agent for lowering the surface tension of 



tMansier, M., 15 Jan. 1908, Bulletin de.la'Socidt^ des Agr. de France. 



