88 



conducted for the past two years in which the compounds 

 Itave been tested on the basis of their sulphur content, the 

 sidphides and polj^sulphides of the different bases being 

 used at varjdng- strengths to give similar ratios of sulphur 

 lespectively in the dilute mixtures. 



In experiments against the San Jose scale, using the 

 compounds at the rate of four and three-fourths ounces of 

 sulphur to a gallon, there were variations in effectiveness 

 on individual trees, especially in apple orchards, which 

 Avere, however, fairly distributed among the various plats. 

 As gauged by blemishing of fruit, production of young 

 scales and infestation of new wood, it was difhcult to per- 

 ceive that one preparation had any appreciable advantage 

 ever another. If the compounds do really differ in eft'ect- 

 iveness, these results suggest that the differences in 

 efficiencies are not great and apparently are such as could 

 easily be overcome either by thorough spraying or by slight 

 .idditions to the sulphur content of the dilute mixtures or 

 by the incorporation of inexpensive substances to increase 

 toxic properties. 



The work in general so far points to the C(nu-lusion 

 that the strength of a preparation Avith regard to its sul- 

 phur content is a more important consideration than the 

 nature of the base of the sulphides and polysulphides. On 

 the assumption that tlie compounds of the dift'erent l)ases 

 are equal or nearly equal against the scale, the chief factors 

 that enter into a choice of a proprietary insecticide are 

 safeness to foliage when combined with arsenate of lead, 

 and economy, in which respects the advantage appears to lie 

 with the calcium and barium sprays, the former being less 

 expensive of the two. 



In tests to determine their values as stomach poisons, 

 none of the compounds alone, apparently, including those 

 of barium, were harmful to various species of leaf-eating 

 caterpillars or beetles. In most instances arsenate of lead 

 with the sulphides and polysulphides of sodium and potas- 

 sium was somewhat quicker in manifesting its toxic 



