COMPOSITION OP LIME-SULPHUfi ANIMAL DIPS. 13 



Solutions exposed to air are oxidized, as is usually represented by 

 the equation : 



(6) CaS x + (x-2) 0=CaS 2 3 -f (x-2) S, 



although it is possible that, as propounded by Divers and Shimidzu, 

 the immediate action is an oxidation of the hydrogen sulphid liber- 

 ated according to equation 4. 



Above a certain concentration of the hot solution, which appears 

 to lie between 3.33 and 3.95 per cent of monosulphur, the following 

 reaction tends to progress from left to right : 



(7) CaS 2 3 ^CaS03+S. 



A well-boiled solution, not originally made with an excess of lime, 

 can never under any circumstances possess a plus reaction figure — 

 that is, it can not contain calcium hydroxid in excess of monosulphur. 

 If originally made with an excess of lime or if not boiled long enough., 

 excess lime is at first present in solution. But if such a preparation 

 be allowed to stand quietly and cool off in the cooking vat, the indi- 

 cations are that the undissolved lime soon settles down, while the 

 small amount of dissolved lime rapidly reacts with polysulphur ac- 

 cording to equation 2, so that in this case, also, unless the cooled 

 solution is again stirred up with the sediment, a plus reaction figure 

 can never be present in the end. But such a solution will naturally 

 contain a notable amount of tetrasulphid. 



As regards the period of boiling, it is not improbable that the time 

 should be increased with increasing concentration. Lime is but little 

 soluble in the solution at any stage, and it probably must dissolve 

 before it can react with the sulphur. It would seem, therefore, that 

 a longer time must necessarily be required in a given volume for a 

 large quantity of lime to enter successively into solution and into 

 reaction than for a small quantity. 



As regards the effect of degree of concentration, in addition to the 

 decomposition of thiosulphate which has been noted, the indications 

 are that with increasing concentration the utilization of both lime 

 and sulphur possibly becomes less nearly complete, and also that 

 the polysulphids formed possibly contain a somewhat less proportion 

 of pentasulphicl. But the apparent effect might have been produced 

 simply by insufficient boiling, and in any event it is of no material 

 significance in comparison with the practical importance of putting 

 out proprietary preparations in highly concentrated form. 



Finished solutions, if stored over sediment which contains free 

 lime, will naturally tend to maintain a plus reaction figure and will 

 undergo changes attributable to the slow progress of reactions 1 

 and 2. If decanted from sediment and preserved from access of 

 air, only two slight changes are noticeable ; first, the progress of 

 equation 5 until a certain concentration of hydrogen sulphid is 

 reached, when equilibrium is established according to equation 4; 



