300 Transactions, 



in situ in a current of air and subsequently reduced and allowed to cool in 

 a stream of dry hydrogen ; after this treatment the hydrogen has been 

 displaced by dry air, and the tube and its contents weighed, c is a weighed 

 calcium-chloride tube, d is a Schiff's nitrometer containing strong potash, 

 with a mercury trap below. 



4. The tubes a, b, c, and d having been arranged in position as shown, 

 the air is displaced from the apparatus by a current of dry carbon-dioxide, 

 conveniently prepared by heating sodium-bicarbonate in a test-tube and 

 passing the gas over pumice moistened with sulphuric acid. When all the 

 air is displaced the copper in b is heated to redness by a group of three 

 or four Bunsen burners, the current of gas being at the same time slackened. 

 The U tube a is now surrounded with hot water, which causes the con- 

 tained bulb to burst, owing to the high coefficient of expansion of the 

 nitric acid. The stream of carbon-dioxide carries the vapour of nitric 

 acid over the red-hot copper, where it is decomposed according to the 

 equation — 



2HNO :! + 5Cu = 5CuO + H 2 + N 2 . 



When no further increase in the volume of gas in d is observed, the nitro- 

 meter is disconnected and the rest of the apparatus allowed to cool in the 

 current of carbon-dioxide. The carbon -dioxide is then displaced from b 

 and c by a stream of dry air, and the increase in the weight of these tubes 

 taken. The composition is then at once arrived at, for 



Hydrogen = i of the increase in weight of c. 



Oxvgen = ^ of the increase in weight of c + the increase in weight 



of b. 

 Nitrogen = Number of c.c. of gas in d (corrected) x 0-00125 gm. 



The ratio of the number of atoms is then obtained in the usual wav by 

 dividing the weight of each of the elements by the atomic weight of the 

 same element respectively. Two experiments carried out on separate 

 preparations of nitric acid by the above method gave — 



(1) H : N : = 1-02 : 1-00 : 2-92, 



(2) = 1-00 : 1-00 : 2-97, 



which are sufficiently near to the required ratio 1:1:3. The time taken 

 from the commencement of passing the carbon-dioxide to the disconnecting 

 of the nitrometer need not exceed half an hour, so that with a little fore- 

 sight the analysis can be conveniently carried out in a lecture of an hour's. 

 duration. 



Since the density of the vapour of nitric acid diluted with air has been 

 shown .to correspond approximately to that required for the formula 

 HN0 3 ,* all the facts required by the student in the establishment of the 

 formula are thus available. 



* Playfair and Wanklyn, " Journal of the Chemical Society," vol. 15, p. 142. 



