NITRE, NITRIC ACID, AND NITROGEN 



207 



charcoal, and provided with a stopcock, could be connected with 

 the bulb A, through the capillary ground-glass joints at K and D. 

 Air could be pumped out or nitric oxide admitted through the 

 stopcock P. 



The bulb A was weighed (i) empty, and (2) filled with nitric 

 oxide. After burning the nickel in the boat H, the nitrogen 

 left in the bulb A was transferred to the bulb M by opening the 



FIG. 40. GRAY'S APPARATUS FOR DETERMINING THE COMPOSITION OF 

 NITRIC OXIDE. 



two stopcocks (after pumping out the air between K and D) and 

 then cooling the charcoal in M by liquid air. The whole of the 

 nitrogen was thus condensed on the charcoal and a vacuum was 

 produced in the rest of the apparatus. A third weighing of the 

 bulb A gave the weight of oxygen which had been taken by the 

 nickel from the nitric oxide ; the increase in the weight of 

 the bulb M gave the weight of the nitrogen that had been set 

 free, thus : 



2NO + 2Ni -> N 2 + 2NiO. 

 In a typical experiment, 

 .6 2I 03 gran, nitric oxide gave {^ g- oxygen^ 



whence I4'oi3 grams of nitrogen combine with 16 grams of 

 oxygen to form 30*013 grams nitric oxide. 



C. NITRIC AND NITROUS ACIDS. 



The existence of two " acids of nitre," one strong and the 

 other weak, was recognised by Priestley, Scheele, Cavendish, 



