Distilled Watersqf our Pharmacopoeias. 577 



more especially the case where oils of considerable age had 

 been employed. By this mode of* operating, the results ob- 

 tained range from 0*50 gr., in the 1000 gr. measures of the 

 water, as in peppermint-water, to 1*20 gr. in dill and pimento 

 waters; many others were tried, which ranged between these 

 two points. It may perhaps be as well here to mention, that 

 it was observed very soon after the application of the heat in 

 evaporating, that flocculi of carbonate of magnesia invariably 

 separated. 



The general opinion has been that these waters were formed 

 in consequence of the magnesia as a base favouring the union 

 of the oil and water, and thus implying some combination of 

 these materials ; but I was led to believe, from various circum- 

 stances presenting themselves during these experiments, that 

 this was not in any respect the true cause, and that the car- 

 bonate of magnesia acted simply as a mechanical subdivider 

 of the oil, if I may be allowed the expression, so that the water 

 acted as a solvent with greatly increased effect upon an enor- 

 mously extended surface of the essential oil, as is the case in 

 distillation, where the cohesive attraction of the molecules 

 being overcome by the influence of heat, the vapours of the 

 oil and water rise together, are mutually diffused and pass 

 over into the refrigerator or worm to be condensed, and thus 

 solution is to a certain extent effected. Under this impression 

 the same experiments were repeated, substituting for the car- 

 bonate of magnesia the kaolin or porcelain clay of Cornwall, 

 or finely-divided silica in the form of powdered flints, and with 

 perfect success, the resulting medicated waters being perfectly 

 colourless, transparent, and having a full flavour of their re- 

 spective oils. On evaporation no residue was obtained, except 

 in a few instances a small quantity of resinous matter, where, 

 as before mentioned, oils had been used which had been made 

 a long time : this amounted in the case of pimento water to 

 0-50 gr. 



Two questions remain now to be settled arising out of the 

 foregoing experiments ; first, does the magnesia enter into 

 combination with the acid oils existent in some of the essential 

 oils used, as pimento, &c.? or, secondly, is the oil simply taken 

 into solution by the distilled water? The fact of the carbonate 

 of magnesia separating from the solution by the application of 

 heat, and remaining always in the state of carbonate on eva- 

 poration to dryness at a temperature of 212° F., is a strong 

 argument in opposition to the first of these questions, as I do 

 not think the view taken by Dr. Pereira is possible, namely, 

 that the magnesia of the carbonate of magnesia first combines 

 with the acid of the oil, which as a consequence, implies the 



Phil. Mag. S. 3. No. 176. Suppl. Vol. 26. 2 Q 



