14 BULLETIN" 451, U* S. DEPARTMENT OF AGRICULTURE. 



second, an apparent slight drop in the thiosulphate figure, for which 

 no explanation is offered, since the phenomenon appeared too quan- 

 titatively insignificant to warrant special investigation. Both 

 changes, in fact, are so slight as to be entirely negligible for practical 

 purposes and under ordinary conditions. 



For the actual preparation of lime-sulphur solutions equations 1, 

 2, and 3 call for the use of 13.7 parts of available calcium oxid 

 to 100 parts sulphur. That the laboratory experiments did not pre- 

 cisely check this theoretical ratio is attributable solely to the decom- 

 positions represented by equations 5 and 6. The decomposition 

 represented by equation 5 is independent of the formula employed 

 and in no way changes the relative proportions of primary in- 

 gredients called for; that is, equation 5, following the postulated 

 escape of hydrogen sulphid, produces neither free lime nor free 

 sulphur, and leaves the solution neutral. There remains then only 

 the matter of oxidation to be considered. But that is a surface action 

 solely, and considering the enormous advantage in the ratio of vol- 

 ume to surface possessed by even moderate-sized cooking vats over 

 laboratory apparatus, it approaches a negligible factor. Therefore 

 the theoretical ratio becomes the actual ratio which should be fol- 

 lowed in practice, provided only the concentration is not sufficient to 

 allow equation 7 to progress from left to right. The formation of 

 sulphite becomes a significant factor when the formula employs some- 

 what more than 20 parts of sulphur per 100 volumes of finished 

 solution. For a number of reasons the writer believes that it will 

 be generally inadvisable to try for a much higher degree of con- 

 centration in " homemade " solutions. Certainty in such solutions 

 no allowance should be made for the formation of sulphite by in- 

 creasing the ratio of lime to sulphur, as the extent of the decomposi- 

 tion is too dependent on the degree of concentration and length of 

 boiling after the solution is otherwise complete. Attempts to make 

 more concentrated solutions are attended by greater difficulty in 

 manipulating the thick liquid and in avoiding loss by boiling over, 

 and moreover involve more loss of the finished solution in the 

 wet sludge, especially since the volume of sludge is increased by 

 deposition of calcium sulphite. 



Nowhere is there evidence of the existence in cold solutions of more 

 sulphur, either free or combined, than corresponds to the formula 

 CaS 5 . On the other hand, a properly prepared homemade solution 

 will contain at most but a small amount of tetrasulphid. It will also 

 contain a very small amount of hydrogen sulphid, some of which 

 may possibly be in the form of calcium hydrosulphid. While rigidly 

 scientific proof that the two apparently definite proportions of, re- 

 spectively, four atoms and five atoms of sulphur to one atom of cal- 

 cium may not, in fact, arise from mixtures of lower and higher 



