THE ELECTRIC CONDUCTIVITY OF NITRIC ACID. 



369 



and silver nitrates dissolved in it, the former to remove any sulphuric acid which 

 might have been mechanically carried over, the latter to remove haloid acids 

 remaining dissolved.* The acid thus obtained was subjected to a third process of 

 fractional distillation t in an apparatus constructed all of glass as follows. 



A (fig. 1) is a distillation flask of about 400 cub. centims. capacity, the neck of 

 which, considerably lengthened out, was sealed at its upper end to the top of a spiral 

 condenser, B, kept cool by a current of ice-cold water ; to the lower end of the latter 

 the receiver was attached, which was provided with a stop-cock for drawing off the 



Fig. 1. 



condensed acid from time to time. A side trap, C, was sealed on to the upper end of 

 the receiver, in order to retain any accidental spirting from the sulphuric acid towers, 

 D and E ; these latter were about half a metre high, and filled for three-quarters of 

 their length with glass beads moistened with sulphuric acid, which could be renewed 

 by means of stop-cocks sealed at their lower extremities. This process of cleansing 

 and renewal was repeated not only previous to, but also during each distillation. It 

 was found by experience that these towers were sufficient to prevent any moisture 

 from passing from the water pump to the anterior portion of the apparatus. The 



* This process of purification was previously adopted by KOLB, ' Aim. Chim. Phys.' [4] vol. 10, p. 140. 

 f Attempts were made to remove the water present by means of phosphorus pentoxide, but were 

 unsuccessful owing to the rapid decomposition of the 99 per cent, acid by this substance. 

 VOL. CXCI. A. 3 B 



