NOTE OM THE ANALYSIS OF SODA-SULT H UK DJ PS. 475 



sible formation of depilaU)ry hytlrosulphide. This point, how- 

 ever, has not yet been specificiall}' investigated. In the event 

 of appreciable amotnits of depilatory lower sulphide being pres- 

 ent, the ratio of monostilphur equivalent to total sulphide sulphur 

 will of course be umisualh^ narrow. In well-made soda-sulphur 

 dips this ratio usually lies between i : 4 and i : 5, i.e., a mixttu^e 

 of tetrasulphide and pentasulphide is indicated. If the ratio 

 is much narrower than i : 4 the dip should be viewed with 

 sus|)icion, and tested by steeping washed wool in it at tank dilu- 

 tion, and then subjecting the fibre to microscopic examination 

 for depilatory action. 



In reporting upon the efficacy of a soda-sulphur concentrate 

 in relation to the eradication of scab, the content of polysuli>hide 

 sulphur should be made the basis of calculation. Other con- 

 stituents, such as thiosulphate, are of negligible parasiticidal im- 

 portance, and need not be considered in evaluation. The dilu- 

 tion recommended for tank strength should be such that the 

 polysulphide does not fall below 0.6 to 0.7 per cent. 



The following sample analyses illustrate the composition of 

 four dififerent concentrates : — 



Grams per 100 c.c. 



Samples A and B are permissible, sample B being practi- 

 cally on the 0.6 per cent, limit for polysulphide sulphur (re- 

 garded as the minimum for efficiency in the treatment of scab), 

 and sample A being well above it and equivalent to a well- 

 prepared home-made dip. From the analysis B is stiggested as 

 being manufactured from cattstic soda and sulphur, while A, in 

 which the thiosulphate is very low, is suggested as being derived 

 by reduction of sodium sulphate. Sample C would also be per- 

 missible if used at twice the strength recommended by the ven- 

 dors. There is no evidence of admixture with depilatory lower 

 sulphide, but the tank concentration only works out at half the 

 strenj^th regarded as necessary. It could not. therefore, be 

 relied upon to cure scab if used according to the specified direc- 



