512 PROFESSOR DITTMAR AND MR C. A. FAWSITT ON 



of which reagent we had not a sufficient stock at our disposal. Nitrate of 

 baryta is heated in a platinum crucible until it ceases to decrepitate. It is then 

 ground up finely, and mixed with its own weight of perfectly anhydrous quick- 

 lime (as obtained by the dehydration of slaked lime at a red heat), the mixture 

 put back into the crucible, and then kept for two to three hours at a red heat, 

 conveniently within a muffle ; to be converted into a mixture of BaO and CaO, 

 of which 100 parts require, by calculation, 24*6 parts of water for conversion of 

 the two oxides into monohyclrates — 4*3 for the baryta, 20*3 for the lime. The 

 platinum crucible remains unattached, and the product is easily reduced to a 

 fine powder. Our general method for these dehydrations was as follows : — 

 The alcohol to be operated upon is analysed approximately by determining its 

 specific gravity ; it is then mixed with only a little more than the calculated 

 quantity of the respective dehydrator, and next " tortured " with it under an 

 inverted condenser. The mixture is then distilled from out of a water-bath, in 

 which the flask is entirely immersed, and the distillation continued as long as 

 anything comes over. The distillate is again operated upon in the same way 

 until two successive distillates, obtained at the baryta-lime stage, exhibit the 

 same specific gravity at the same temperature. At the later stages of the 

 dehydration the receiver is connected with a " vitriol tower" to keep out 

 atmospheric water, and all unnecessary transvasations are avoided, the flask 

 intended for distillation serving as the receiver in the preceding one. For the 

 determination of the specific gravities we generally used a Westphal balance; in 

 the later stages we determined the difference of specific gravity between two 

 successive distillates by means of the differential method, which one of us 

 described in the Chemical Neivs, vol. xliv. p. 5, some years ago. The idea which 

 guided us was to effect a complete dehydration with the least possible loss of 

 alcohol as alcoholate of baryta or lime. 



We felt quite sure that a methyl-alcohol which suffered no diminution of 

 specific gravity on renewed distillation over baryta-lime really is anhydrous ; 

 yet some doubts about this arose in our minds at a later stage, and we distilled 

 a presumed to be anhydrous alcohol over dehydrated sulphate of copper. 

 The result was that the specific gravity suffered a measurable diminution. 

 Possibly the alcohol then operated upon had attracted a little moisture from 

 the air (notwithstanding the care with which it had been protected) since its 

 final treatment with baryta-lime. We did not inquire into this point, but made 

 it a rule henceforth not to accept an alcohol as anhydrous unless it had been 

 made constant in specified gravity by means of, ultimately, dehydrated sulphate 

 of copper. 



As the result of a long and tedious series of dehydrations, we came into 

 possession of a few litres of baryta-lime proof methyl-alcohol, and the question 

 was to prove its freedom from organic impurities. As a first step towards this 



