THE ELECTRIC CONDUCTIVITY OF NITRIC ACID. 



TABLE I. 



373 



For the determination of the nitric acid solutions a weighed quantity was expelled 

 from a pyknometer, neutralised by a slight excess of the standard sodium hydrate, 

 and the amount of such excess added determined by a solution of hydrochloric acid of 

 Too equivalent strength of the soda. 



STANDARDISATION OF THERMOMETERS. 



The thermometers employed were graduated to '1 C., and were compared with 

 (i.) a standard Kew thermometer which could be read to '05 F., and (ii.), within 

 certain limits, with another standard graduated to '05 C., constructed by BAUDIN 

 and formerly in the collection of the 8th Duke of MARLBOROUGH. 



The zero displacements of all the instruments were determined by immersing them 

 in a cylinder filled with washed ice, and surrounded by an outer jacket packed with 

 the same material. The readings were made with a telescope, furnished with cross 

 wires and mounted on glass plates, after the manner of QUINCKE'S reading microscope. 

 For the estimation of the errors at higher temperatures, the thermometers were 

 suspended in a deep tank (containing several gallons of water), so that the thread of 

 mercury at the point to be observed was just visible above the surface ; the instru- 

 ments were arranged in a line with the standard in the middle, so that by a slight 

 rotatory movement of the telescope stand each of them could be brought into the 

 field of view in rapid succession. The water was warmed about 2 above the point 

 required, allowed to cool slowly, while thoroughly stirred, and a first set of readings 

 taken ; the process of stirring was repeated, and a second set taken ; in case of any 

 variation, the mean value was accepted. At the commencement and conclusion of 

 each set of observations, the standards were read, and .their constancy throughout 

 was regarded as a safe criterion that the temperature of the large mass of water had 

 not appreciably altered. The whole series of observations was repeated for every 5 

 within the range required, and in the case of two thermometers found to be less 

 uniform in bore than the others, readings were taken at an interval of each degree. 



