active agents in killing insects. This theory of the action of the wash would also explain why it continues to be efficacious over a considerable length of time. In a wet climate, on the other hand, if a heavy rain should occur a day or two after the wash was applied, all the thiosulphate which was originally present, together with that which had been formed by the decomposition of the pentasulphid would probably be washed away. No sulphite could then be formed by slow decomposition of the thiosulphate. There would, therefore, be left upon the tree free sulphur as the only compound having insecticidal properties. The efficacy of the wash would, therefore, be much reduced. Again, if light rains occurred occasionally after the wash had been applied, its efficacy would be reduced just in proportion to the amount of thiosulphate and sulphite washed away. It has been suggested by Mr. F. H. Pough, manager of the Bergen Port Sulphur Works of New York City, that the efficiency of the limesulphur-salt wash was due almost entirely to the finely divided sulphur set free on the decomposition of the pentasulphid. In support of this the widespread use of sulphur as a fungicide and insecticide was cited, more particularly its use for the prevention of the powdery mildew in vineyards, where it is often sprinkled on the hot ground to the windward of the plants, as well as on them; also to the value of sulphur dusting to destroy the red spider of citrus trees. It is believed by Mr. Pough that the action of the wash is to be attributed to the gradual oxidation of sulphur which gives rise to sulphur dioxid, or sulphurous acid, where moisture is present, and that it is these constituents that do the work. In support of this theory he cites the cases where an odor resembling sulphur dioxid is plainly discernible on hot sunny days in the vicinity of orchards sprayed with the above mixture. While the writer does believe that finely divided sulphur is one of the active insecticidal agents in the wash, though just how it acts is not known, he is inclined to doubt very much whether this oxidation of the sulphur alone would be rapid enough to be of great value. The following points are against this theory: (1) If the action were at all considerable, it would be expected that the total sulphur on the tree would decrease, since not all the sulphur dioxid formed would be likely to be absorbed by the calcium hydroxid or calcium carbonate present, these being only mechanically mixed with the sulphur. In the "paper experiments," which to be sure are artificial, no loss of sulphur was shown after four weeks. (2) It would be expected that the free sulphur would decrease during the course of four weeks by conversion to sulphur dioxid; instead of this, it increases to a slightly greater extent than corresponds to the amount of sulphur formed from the breaking up of thiosulphate, according to the following equation: (3) In regard to the odor resembling that of sulphur dioxid observed by Mr. Pough, those who have sublimed sulphur know that during sublimation this odor is very noticeable, so that the odor noticed in the vicinity of orchards on a hot sunny day may be due to subliming sulphur. On the whole, while it is believed that some of the finely divided sulphur is oxidized, it seems doubtful whether enough is oxidized to make this factor a major one in determining the efficiency of the wash. It seems more probable that the combined action of all the sulphur compounds present, exclusive of the sulphate, gives to the wash its value. THE LIME-SULPHUR-SALT-SODA WASH. Having completed the study of the lime-sulphur-salt wash and the lime-sulphur wash prepared by various formulas and under different conditions, experiments were next undertaken along similar lines with the lime-sulphur-salt-soda and the lime-sulphur-soda washes. These washes have been suggested as substitutes for the older wash, without the soda, since it is said they can be prepared without any or with a minimum amount of boiling, thus saving the farmer much time and trouble. LIME-SULPHUR-SALT-SODA WASH PREPARED WITHOUT EXTERNAL HEAT. The first experiment was to determine the composition of a limesulphur-salt-soda wash prepared without external heat and compare it with that of a lime-sulphur-salt wash containing the same amounts of lime, sulphur, salt, and water, but boiled until the maximum amount of sulphur was dissolved. The following formulas and methods of procedure were followed, using chemically pure reagents: For the lime-sulphur-salt-soda wash 30 pounds of lime, 20 pounds of sulphur, 15 pounds of salt, 10 pounds of caustic soda, and 60 gallons of water were used, and for the lime-sulphur-salt wash the same formula was employed exclusive of the caustic soda. The sulphur was made into a thin paste with 9 quarts of hot water, the lime slaked with 9 gallons of hot water, and the sulphur paste added to it. Then the caustic soda was stirred in and the mixture boiled of itself for a considerable period. Salt was then added and the requisite amount of water to make up 60 gallons plus the space occupied by the solids, as determined by previous tests in the experiments with the lime-sulphur-salt wash. The lime-sulphur-salt wash was prepared by simply boiling the constituents together and making up to volume as in the previous experiments. The results given in Table XIX were obtained: TABLE XIX.-Lime and sulphur in 100 cc of the lime-sulphur-salt-soda wash, a a The various sulphur compounds present in this mixture were not determined. It is evident from these data that all of the sulphur is not dissolved by the heat generated by the caustic soda, and, further, that the sulphur that does go into solution does so to a great extent as the sodium, instead of the calcium, salts of the sulphur acids, thus causing a smaller amount of calcium oxid to be dissolved and a larger amount to remain as a residue than in the case of the lime-sulphursalt mixture. LIME-SULPHUR-SALT-SODA WASH PREPARED BY HEATING FOR A SHORT PERIOD. Since the preceding experiment showed that the method of preparation of the lime-sulphur-salt-soda wash, without the aid of heat, did not dissolve all the sulphur, another experiment was made to determine whether the maximum amount of sulphur would be dissolved by heating for a very short period. The following results were obtained using chemically pure reagents, the same formulas as in the preceding case, and a 20-minute period of heating, that being the time necessary to bring the mixture from room temperature up to the boiling point. TABLE XX.-Lime and sulphur in 100 ce of the wash prepared with 20 minutes' heating. TABLE XXI.--Sulphur compounds in 100 ce of the liquid portion of the wash prepared with 20 minutes' heating. The following facts are indicated by Tables XX and XXI: (1) Practically all of the sulphur goes into solution in the lime-sulphur-saltsoda wash when it is heated for 20 minutes. (2) This treatment seems to dissolve a little more sulphur than by boiling with lime and salt for one hour. (3) The liquid portion of the lime-sulphur-salt-soda wash prepared as above contains the same sulphur acids in nearly the same amounts as the lime-sulphur-salt mixture, the only difference being that the sulphur compounds are present to a large extent as the sodium, instead of the calcium, salts. (4) More residual calcium oxid is present in the lime-sulphur-salt-soda wash than in the lime-sulphursalt wash. (5) The former wash should be more caustic than the latter, both on account of the caustic soda present and also because of the greater excess of lime. LIME-SULPHUR-SODA WASHES PREPARED WITHOUT EXTERNAL HEAT AND BY ADDING CONSTITUENTS IN DIFFERENT ORDERS. The next experiment was for the purpose of determining how much sulphur goes into solution when high grade commercial sulphur, stone lime, and caustic soda are used instead of the chemically pure articles, and what influence the order in which these ingredients are added has on the composition of the wash. For this purpose a wash was first prepared according to the following formula: Lime, 30 pounds; sulphur, 15 pounds; water, 50 gallons, boiling for one hour and using high grade commercial ingredients. This wash was used as the standard and another wash was prepared, using the same amount of ingredients with the addition of 6 pounds of caustic soda to generate the heat and form a good medium for dissolving the sulphur. The following procedure was followed in the preparation of the second wash: The sulphur was made into a thin paste with hot water and added to the slaking lime. When the lime had ceased to slake, the full amount of caustic soda was added and the mixture stirred for 15 minutes. Water was then added to make up to 50 gallons plus the space occupied by the solid reagents. This wash is designated as experi ment 2. In another sample of wash the same formula was used, but the order in which the ingredients were added was different, i. e., the sulphur was made in the form of a thin paste with hot water and the total caustic soda then added. The mixture was stirred for 15 minutes and the lime added and allowed to slake; water was then added to make up to 50 gallons plus the space occupied by the solid reagents. The mixture so made is designated as experiment 3. The following results were obtained with these three washes: Num TABLE XXII.-Lime and sulphur in 100 ce of washes differently prepared. Residual Total sulphur. Grams. Grams. Grams. 3.16 0.24 3.40 2.27 1.13 3.40 2.80 .60 3.40 TABLE XXIII.—Sulphur compounds in 100 ce of the liquid portions of washes differently From these tables it is evident that high grade commercial samples of lime, sulphur, and soda, when used to prepare the lime-sulphursoda wash, act practically the same as the chemically pure articles, resulting in the formation of a mixture containing about the same relative quantities of soluble sulphur compounds, though the amounts are decidedly smaller than those dissolved by boiling. Further, a better wash, i. e., one containing more sulphur in solution, is obtained by adding the ingredients in the order-sulphur, caustic soda, lime-than by mixing in the following order-lime, sulphur, caustic soda. COMPARISON OF THE LIME-SULPHUR-SODA AND THE SULPHUR-SODA WASHES PREPARED WITHOUT EXTERNAL HEAT. A comparison was next made of the composition of two washes, the first of which was prepared according to the following formula: Lime 30 pounds, sulphur 15 pounds, water 50 gallons, caustic soda 6 pounds, adding the constituents in the order-sulphur, caustic soda, lime--just as described in the preceding experiment. The second of the washes was prepared in the same way and by the same formula except that no lime was used. To make the comparison it was only necessary to examine the liquid portions of the washes. The following results were obtained, using high grade commercial ingredients: TABLE XXIV. -Sulphur compounds in 100 cc of the liquid portion of two washes prepared without external heat. |