Conductivities and Viscosities in Formamid. 



21 



produced a smaller loss of materials from combination with it than any 

 of the other dehydrating agents studied. 



Formamid was therefore allowed to stand for several weeks over 

 anhydrous sodium sulphate, in carefully sealed, glass-stoppered bottles, 

 and placed in a cool, dark room. An attempt was made to effect a 

 preliminary purification of formamid by fractional crystallization; 

 but the end-product, after several fractionations, invariably showed a 

 higher conductivity than the original substance. We were therefore 

 forced to conclude, as were Freer and Sherman in preparing formamid 

 to study its sodium salts, that a properly conducted distillation was the 

 best process available. 



FIG. 5. 



The apparatus finally adopted for distillation is shown diagrammati- 

 cally in figure 5. By placing the various parts in parallel rows it was 

 possible to mount the whole apparatus upon a desk-space of only 2| 

 feet square, as is shown in the photograph (plate 1). This condensed 

 arrangement of the apparatus given in figure 5 is photographed in two 

 views in plate 1, and is the perfected apparatus with the exception of 

 the distillation head and the position of the manometer. 



In this apparatus, with all the stopcocks closed, a vacuum of 0.5 mm. 

 was easily maintained by the Gaede pump (fig. 5, K). This pump was 

 mounted, together with a T Vhorsepower motor (fig. 5, L), controlling 

 rheostat not shown, idler (fig.5,M), and switch, on a heavy maple wood 

 base, provided with carrying handles and rubber feet. 



During the actual process of distillation the vacuum rose to from 1.5 

 to 2.5 mm., since, on account of the high viscosity of the liquid, it 

 was necessary to keep a fairly rapid current of air flowing in through 

 the stopcock and drawn-out portion of the distillation head (fig. 5, E), in 

 order to keep the liquid agitated and prevent the violent bumping 

 which usually attended distillation in a high vacuum. The drying of 

 this current of air sufficiently, and the proper method of introducing it, 

 proved to be among the most serious difficulties encountered. The 

 method finally adopted is shown in figure 5. The air, before entering 



