r)4() Journal of the Department of Agriculture. 



possible effect, to wliich reference will be made later. Analysis of the 

 distilled water showed that it contained rather more than 5 grammes 

 of the g-as in 100,000 c.c, wliich is quite an appreciable quantity. 

 Since analysis of the fountain water showed it to contain only one- 

 third of that amount, ii is obvious that the vastly greater separation 

 of oils from the mixtures made with fountain water must be due to 

 some other cause than that of dissolved carbon-dioxide. It was also 

 found that the separation of oils from the fountain water emulsions was 

 not immediately complete, although it was practically so in the case 

 of distilled-water emulsions. 



Solutions of manj^ salts, including common ^alt (as, for instance, 

 " brak " water), have a very powerful effect in destroying these 

 emulsions, but the amount of salt in the fountain water is not nearly 

 sufficient to produce such a result. The fountain water, however, 

 contains carbonates of calcium and magnesium; it is to them that we 

 must look as the principal agents which renijer the fountain water so 

 unsuitable for mixings with dip " A." 



Let us now see how their action can be explained. 



Earlier in this article it is stated that the emulsification of these 

 dips on admixture with water is effected through the agency of sodium 

 abietate, the active constituent of rosin soap. The abietates of calcium 

 and magnesium are insoluble in water, so that, when rosin .soap is 

 mixed with water containing soluble compounds of these elements, it 

 will be decomposed. Applying this to dip, it follows that if sufficient 

 of its rosin soap is destroyed by the calcium and magnesium compounds 

 contained by the water, a perfect emulsion cannot form or, if it does 

 form, it will be broken down. It would therefore seem that Mr. 

 Fincham's opinion quoted higher up is vvell founded. Still, other 

 factors may operate in destroying- these emulsions which, in some 

 respects, are like colloidal suspensions, as, for instance, suspensions of 

 clay. Sometimes these are very stable, sometimes not. Small quan- 

 tities of salts, including common salt, calcium and magnesium 

 chlorides, sulphates, and bicarbonates have a very powerful effect in 

 upsetting permanent suspensions of this kind; there would seem to be 

 little doubt that they are similarly effective in upsetting the 

 equilibrium of the emulsoid suspensions formed by mixing coal-tar 

 dips with water. 



Salts break up clay suspensions by causing the ultra-microscopical 

 particles of clay to aggregate, viz., they flocculate the clay particles. 

 In an emulsion of dip one has, in place of solid particles, ultra-micro- 

 scopical liquid oily particles in suspension; so exceedingly small are 

 they that they pass readily through the pores of the finest filter 

 papers, and, like deflocculated clay particles, are able to remain in 

 uniform suspension throughout the water. When, however, the water 

 is one that acts in a direction cpposite to the dispersive action of the 

 soap (such a water is one which contains appreciable amounts of any 

 of the salts mentioned above), there is every possibility ox the emulsion 

 being flocculated, or broken up. Suspensions of clay in natural waters 

 may be sometimes flocculated by carbon-dioxide; the possibility of 

 this gas acting on dip emulsions in this manner must, therefore, not 

 be overlooked. 



In order to test whether the free carbon-dioxide in the fountain 

 water exerted any appreciable effect in destroying the emulsion of 



