228 ELEMENTARY AGRICULTURAL CHEMISTRY 



The calcium monosulphide, CaS, can, however, dissolve an addi- 

 tional quantity of sulphur, to form, finally, calcium penta- 

 sulphide, CaS^, thus : 



CaS + 4S = CaS,. 



So the maximum amount of sulphur which can be dissolved by 

 boiling with lime and water is indicated by the equation : 



3CaO + 12S = 2CaS5 + CaSfi^. 



Taking atomic weights Ca = 40, O = 16, S = 32, 



3(40 + 16) = 168 1ime. 12 x 32 = 384 sulphur. 



168 parts of pure lime can thus bring about the solution of 

 384 parts of sulphur — i.e., 1 part by weight of lime suffices to 

 dissolve 2*28 parts of sulphur, or 1 lb. of sulphur requires 

 0"4375 lb. of pure lime. Now ordinary lime is never pure ; 

 the proportion of real lime present varies from as low as 

 50 per cent., or even lower, to as high as 98 per cent., 

 or higher. Hence those recipes which give lime to sulphur 

 in less proportion than 1 to 2, even if the lime be of good 

 quality, must leave a large proportion of the sulphur un- 

 dissolved. With the usual qualities of lime the amount of 

 sulphur in excess will be still greater, and when, as is generally 

 recommended, the liquid is allowed to settle and only the clear 

 portion used for dipping much sulphur is wasted. It is, on 

 the other hand, desirable to avoid excess of lime in the dip, 

 otherwise the injury to the wool becomes greater. The proper 

 propoitions of lime and sulphur to use will depend greatly 

 upon the purity of the former, If the lime be white, freshly 

 burnt, and slakes with considerable heat when water is added, 

 it is probably fairly pure, and 1 part of lime to about 2J parts 

 of sulphur will be about the right proportion. But if *' blue 

 lime " be used, and especially if it be partly " air -slaked " — i.e., 

 has been kept for some time — equal weights of lime and 

 sulphur will probably be better. In any case it will be safer 

 to see tha^< there is at the end of the boiling a little sulphur 



