12 BULLETIN" 451, U. S. DEPARTMENT OP AGRICULTURE. 



It is interesting to note the change in reaction figure between sam- 

 ples E-l and E-2. The change is, of course, perfectly logical, for the 

 hydrogen sulphid which produces the negative reaction figure be- 

 comes simply sulphur and water upon oxidation. In deducing the 

 equation to express oxidation, it is accordingly necessary in this case 

 to employ the sulphicl-base figures and not the sulphid-acicl figures. 

 The change of sulphicl-base figure from sample E-l to sample E-2 

 is 28.13-15.51 = 12.62 loss, which, according to the accepted equation 

 CaS x -[-30=CaS 2 3 -j-( x -— 2)S, should be balanced by a gain of one- 

 half as much, or 6.31, in the thiosulphate figure. The actual gain in 

 the thiosulphate figure in the experiment was 6.24, which is in reason- 

 able agreement. 



CONCLUSIONS. 



The reactions which determine the composition of lime-sulphur 

 solutions, besides being rather numerous, are some of them reversible, 

 the points of equilibrium varying according as the solution is hot or 

 cold, dilute or concentrated, or exposed to the influence of other vary- 

 ing conditions. Under such circumstances the only way in which 

 laboratory studies can be of practical value is by so thoroughly estab- 

 lishing the fundamental principles involved and the effect of varying 

 conditions upon the relative importance of such principles as to afford 

 a sound basis for reasoning. 



It appears that when lime and sulphur are boiled with water, ignor- 

 ing unessential and hypothetical intermediate compounds, the follow- 

 ing reactions occur : 



(1) 3Ca(OH) 9 +12S=2CaS 5 +CaS 2 3 -f3H 2 



(2) 10CaS 5 +3Ca (OH) 2 =12CaS 4 +CaS 2 3 +3H 2 



(3) CaS 4 +S=CaS 5 



Only when substantially all free sulphur has been dissolved will 

 equation 2 become operative or equation 3 fail to hold all poly- 

 sulphid substantially up to the pentasulphid. 



All lime-sulphur solutions are subject to hyclrolytic decomposition 

 according to the equation : 



(4) CaS x +H 2 O^Ca(OH) 2 +H 2 S+(x-l)S, 



the pressure of the reaction from left to right increasing with rise of 

 temperature. Whether or not hydrogen sulphid can escape, the 

 remaining products on the right-hand side react according to equa- 

 tion 1, giving as final result, in case of CaS 5 , 



(5) CaS 5 +3H 2 0=GaS 2 3 +3H 2 S. 



Thus all solutions are in equilibrium only when they contain a cer- 

 tain excess of hydrogen sulphid, the amount being dependent upon 

 the temperatures and concentrations of the solutions. 



