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The potassium polysulphide used in the experiments was in the form 

 of tiles weighing about 2 lb. each. These were very hygroscopic, and 

 if broken up small, they dissolved quickly even in cold water. In the 

 experiments a 33-| per cent, solution was produced by dissolving 

 10 lb. of potassium polysulphide in 2 gals, of water and then diluting 

 up to 3 gals, of liquid. This stock solution was kept in tightly closed 

 glass bottles ; at a temperature of 58° F. its density was 1-23. Both 

 the 2 per cent, and 8 per cent, working strength were less frothy than 

 those of polysulphide of calcium, even with the addition of the boiled 

 paste. Strong solutions, such as 5 per cent, and 7 per cent., were very 

 viscid to the touch owing to their alkalinity, and they somewhat affected 

 the skin. They never damaged the rubtjer hose, whether cold or hot. 

 In cases where the calcium and potassium polysulphides were mixed, 

 flocculent tufts were formed — even when the two solutions were clear 

 before mixing. Though the mixture was somewhat viscid, it did 

 not stick to the citrus leaves and therefore required the addition of 

 the paste. With such an addition, it yielded on drying a coating 

 which was highly resistant to atmospheric agents, and this property 

 is the more marked when the polysulphide of calcium is predominant. 

 For instance, a spray containing 2 per cent, of polysulphide of 

 potassium, 4 per cent, of the concentrated solution of polysulphide 

 of calcium and 2 per cent, of flour, was very adherent to the foliage 

 and resisted well the action of rain. The leaves of citrus plants are 

 able to resist chemical action to a considerable extent, and in December 

 calcium polysulphide was safely applied at a strength of 14 per cent. ; 

 in summer 5 per cent, was found to scorch the young fruit if applied 

 in the hot hours of the day, but not at other times. The potassium 

 polysulphide was variable in action according to the dampness of the 

 atmosphere, the temperature being a less important factor ; in July 

 a 7 per cent, solution destroyed the Coccids and did little damage to 

 leaves or fruit. In autumn, however, the same dose injured many 

 leaves and fruit, and a dose of 2 per cent, of the solution containing 

 both polysulphides also proved injurious. In no case should the 

 polysulphides be applied when the citrus plants are in blossom. Even 

 at doses of 3 or 4 per cent, polysulphide of potassium had a very 

 powerful and comparatively prompt action on the Coccids. The 

 males were even more sensitive to it than the females, and the nymphs 

 succumbed very quickly; to mobile larvae a dose of 0*4 per cent, 

 proved fatal. The immunising action of polysulphide of potassium 

 was also very strong and lasting, unless there was rain. Polysulphide 

 of calcium behaved in a very different manner. Its action on the 

 Coccids, though efficient, was much slower. In the early nymphal 

 forms the mortality was ascertainable after 8-10 days, but with the 

 adults a 5 per cent, dose required a fortnight or more to reveal its 

 efficiency. Spraying should be done from June to September and 

 after harvesting the crop, up to early in March. In the experiments 

 good results were obtained both in summer and winter, but in Sicily 

 the summer is preferable as rains are then less frequent, while winter 

 treatment may mean several applications and a waste of material. 

 In summer, with maximum temperatures of 104° F., two applications 

 of 5 per cent, polysulphide of calcium removed all infestation. If the 

 applications were put off until the crop had been gathered, a stronger 

 dose of 7 or 8 per cent, was necessary. If the weather was not rainy 



