522 PROCEEDINGS OF THE AMERICAN ACADEMY, 



temperature of the liquid should never exceed the true boiling point of 

 the mixture. 



Very considerable superheating occurs when a liquid is boiled in 

 a glass flask by the application of heat from outside. On the other 

 hand, we found that very little superheating of a liquid occurs when 

 the liquid is heated by means of an electric current passing through a 

 suitable resistance wholly immersed in the liquid. S. Lawrence Bige- 

 low has suggested this methqd of heating in the determination of the 

 molecular weights of a substance in solution by measuring the eleva- 

 tion in boiling points ; its satisfactory application to this problem is 

 an indication of its efficiency in obviating superheating. It is clear, 

 therefore, that the electrical method of heating might be expected to 

 give more complete separation during the process of practical distilla- 

 tion than the ordinary method. 



The matter is so obvious that probably others have thought of this 

 before ; but because we have never seen the method in use, nor have 

 been able to find a reference to it in chemical literature, we venture to 

 call attention to it in this brief paper. 



The extent of the increased efficiency is best indicated by two par- 

 allel experiments, alike in every essential respect except the difference 

 in the source of heat, and the fact that into the ordinary boiling flask 

 Markovnikov capillary tubes were placed to relieve the superheating 

 to some extent. Even with this precaution added to the old way, the 

 diff'erence in result was very marked, as the following figures show. 



0.1 liter of a specimen of normal butyl alcohol, dried with anhydrous 

 copper sulphate, needed sir distillations in order to secure 75 milli- 

 liters of liquid boiling within the limits of 1 degree (117.0°-118.0° at 

 759 mm.), using the ordinary method of outside heating by a gas 

 flame. 



The same volume of the original liquid by only two fractional distil- 

 lations with electrical heat yielded the same volume of distillate of a 

 much higher grade of purity, having boiling-point limits only 0.6 apart 

 (117.3°-117.9°). 



Similarly, 120 milliliters of ortho cresol which in one distillation 

 gave 100 milliliters within 0.8° (190.0°-190.8° at 765,0 mm.) gave an 

 equal amount boiling within 0.3° (189.9°-190.2° at 758.5 mm.) by the 

 new method. Numerous other examples might be cited, but these 

 are sufficient to show the great advantage to be derived from electrical 

 heating. 



A word concerning an advantageous form of apparatus is not out of 

 place, although a heating resistance-coil may be immersed under the 

 liquid in any ordinary distilling apparatus. In order to economize 



