40 Mr. V. H. Veley. The Conditions of the [June 2, 



Certain experiments were made upon the action of dry nitric 

 oxide npon nearly anhydrous nitric acid (sp. gr. 7/7 = 1'5326), the 

 preparation of which has been described in a previous section. The 

 air was driven out of the apparatus by a current of carbonic acid 

 dried by passage through a wash-bottle containing concentrated 

 sulphuric acid, and then through three drying tubes filled with 

 pumice and phosphorus pentoxide. The nitric acid was contained in 

 the Geissler's bulbs as before (kept at a temperature of 11), and 

 subsequent to them was another wash-bottle of sulphuric acid to pre- 

 vent the access of moisture by backward diffusion. 



On passage of the nitric oxide gas, the portion of acid in the first 

 bulb was turned a yellow tint, which gradually deepened to an orange- 

 red ; when about a litre of the gas had been driven through a red 

 oil appeared floating upon the surface of the acid, and a few minutes 

 after the red oil turned a green tint, and for some time there were 

 two distinct liquids of different densities in the bulb, but afterwards 

 a green uniform liquid was obtained. Meanwhile the portion of acid 

 in the second bulb had deepened in tint, then the red oil was formed, 

 and the other phenomena in due succession. (The weight of the acid 

 at this point had increased.) When about 4 litres of nitric oxide had 

 passed in the green liquid in the first bulb gradually turned to a 

 blue, which slowly evaporated into the second bulb, and eventually 

 only a few drops of an almost colourless liquid were left. Simul- 

 taneously the portion of acid in the third bulb showed the transition 

 tints of yellow to orange with ultimate formation of the red oil, and 

 also dense red fumes passed out of the acid. At this point the ex- 

 periment was stopped, and the weight of the nitric acid was found to 

 have considerably decreased. 



The explanation of these changes, which were observed in part 

 by Priestley* at the end of the last century, seems to be as follows : 

 At first nitrogen peroxide is formed by the mutual oxidation of the 

 nitric oxide and reduction of the nitric acid, and this is retained in 

 solution by the excess of the acid 



2HN0 3 + 2NO = 3N 

 A point is reached at which the acid becomes supersaturated, and the 



. . . qui se deVeloppent egalement par 1'action du bioxyde d'azote sur 1'acide 

 azotique a differents degres de densite. 



' Le produit vert . . se forme aussi par le contact du bioxyde d'azote avec 

 1'acide hypoazotique, et sa production pouvait etre tout a fait independante de 

 1'eau " (as shown by experiment). 



" Experiments and Observations on different kinds of Air," vol. 1, p. 383. I 

 may be allowed to allude to the section of this work relating to nitrous acid, which 

 contains a number of observations upon its properties ; several of them appear to 

 have been published as novelties many years afterwards. 



