Roberts — Reduction of Nitric Acid by Ferrous Salts. 129 



ing when the nitrate was introduced, a higher oxide of nitro- 

 gen was evolved in quantity sufficient to be visibly red, while 

 the oxidation of the ferrous salt in the residue fell to ninety 

 per cent of its normal value. 



These facts and the consideration that the analytical methods 

 in which the nitric oxide is estimated give without, exception 

 unexpectedly low results have led me to look a little more 

 carefully into the conditions under which the reaction of fer- 

 rous salts upon the nitrate may be expected to give the volume 

 of nitric oxide most nearly approaching the theoretical yield. 



The apparatus which I have found most satisfactory for this 

 work consists of a small tubulated retort, upon the neck of 

 which is fitted a small condenser to prevent loss of liquid dur- 

 ing the distillation. Into the tubulature of this retort is fitted 

 tightly, by a carefully ground joint, a tube drawn out so as to 

 dip below the surface of the liquid, and fitted with carefully 

 ground stop-cocks, — as shown in the figure, — and so branched 

 above as to make it possible to transmit carbon dioxide through 

 the apparatus, or to admit any liquid without admixture of air. 

 The condenser is joined to a Will and Yarrentrapp bulb used 

 as a trap, and this in turn is connected by thick vacuum tub- 

 ing with a Hempel gas-burette. Carbon dioxide was generated 

 in a Kipp's apparatus by action of boiled hydrochloric acid 

 upon boiled marble, and the liquid was charged with cuprous 

 chloride, following Warrington's device, to take up traces of 

 dissolved oxygen. Notwithstanding all precautions, I have 

 met with the generally recognized experience in finding that 



