RECENT WORK IN AGRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY— AGROTECHNY. 



A report of chemical investigations on the lime-sulphur spray, H. V. Tar- 

 tar {Oregon Sta. Research Bui. 3 (1914), pp. 28). — The first investigation re- 

 [)ortecI in this bulletin has been noted previously from another source (E. S. 

 R.. 23, p. 701). 



The primary action between sulphur and calcium hydroxid was studied 

 because the investigations cited in the literature did not include this phase 

 of the sul)ject and the work in general on this topic was imperfect. In the 

 literature it is shown that the products resulting from the reaction of sulphur 

 with the alkali and alkaline earth hydroxids are polysulphids and thiosul- 

 phates, but in practically all of the investigations air was not excluded from 

 contact with the products of the reaction. This caused an error due to the 

 rapid oxidation of the polysulphids. Most of the experiments were also made 

 with an excess of sulphur and probably witliout considering a possible second- 

 ary reaction of the sulphur with the pro(^lucts formed by a primary reaction. 

 Previous "vv'ork was also handicapped by the lack of methods for determining 

 the amount of the hydroxid of a metal present in solutions also containing 

 polysulphids and thiosulphates of the same metal. 



"The primary reaction between calcium hydroxid and sulphur in heated 

 aqueous solution tr.kes place as represeiited by the following equation : 

 3Ca(OH)2+10S=2CaSi+CaS.03+3H.O." 



The reaction resembles that occui'ring with potassium hydroxid and sulphur 

 with the exception that with potassium hydroxid the trisulphid (K^S^) is 

 formed. "When sulphur is used in excess, a secondary reaction occurs, in 

 which it combines with the calcium tetrasulphid to form the pentasulphid." 



When considering the theoretical basis for the proportion of lime and sulphur 

 used in the preparation of lime-sulphur solution, it is pointed out that 

 although some difference still exists in the recommendations made by the 

 diffei'ent experiment stations, the more recent work shows the proper propor- 

 tion of lime and sulphur to be approximately 1: 2. 



" The compounds formed by the reaction between calcium hydroxid and sul- 

 phur, under ordinary commercial conditions of manufacture, are calcium tetra- 

 sulphid, pentasulphid, thiosulphate, and sulphite. All of these comiK)unds are 

 readily soluble in water with the exception of the sulphite, which is compara- 

 tively insoluble." The chemical analysis of a lime-sulphur solution, therefore, 

 will show the amount of lime and sulphur which have reacted to form the same, 

 with the exception of these substances necessary to form insoluble sulphites. 

 The equation given above " shows that when calcium hydroxid and sulphur 

 combine, one-thii"d of the calcium is combined as thiosulphate and two-thirds 

 as polysulphid. Since there is no decomposition of the polysulphid, the quan- 

 titative estimation of the calcium combined in this form gives a means for 

 determining the amount of thiosulphate which has been formed. The difference 



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