80 § 60. BASES AND ACIDS WITH llEAGENTS. 



again at c?, the water will rise in the tube leading from 

 A to -S, and, if the apparatus is tight, will remain at a 

 stationary level above that of the water outside of the 

 tube. Now, weigh the whole apparatus, apply suction at 

 d to cause a little nitric acid to flow over into A from 

 time to time, and in this manner keep w^ a slow evolution 

 of carbonic acid ; when all the carbonate is decomposed, 

 and all the nitric acid transferred to the flask, apply a 

 little heat to the latter ; then, by suction at c?, draw air 

 through the apparatus as long as any acid taste is per- 

 ceived in the gas, let the apparatus cool, and weigh it. 

 The air should be caused to j^ass through a calcic chloride 

 tube before it goes into the apparatus, in order to dry it 

 thoroughly. 



The loss of weight suffered by the whole apparatus 

 equals the carbonic anhydride, CO^. 



This method, otherwise very convenient, is, according 

 to Prof. S. "W". Johnson, {American Journal of Science 

 and Arts ^ Second Series^ 48, 111) liable to the objection, 

 that in freeing the apparatus completely from carbonic 

 acid, some vapor of water escapes the desiccating materi- 

 al. He therefore proposes to fill the apparatus with car- 

 bonic acid gas before weighing it, and then to weigh it 

 again as soon as the decomposition of the carbonate is 

 completed ; it is essential only, that the substance under 

 examination dissolve freely in cold acid, and that the 

 analysis and weighings be conducted in an apartment not 

 liable to changes of temperature. 



His apparatus may be closely imitated by substituting 

 for the acid reservoir in the above figure, another one 

 consisting of a bulb of sufficient size blown on a tube of 

 which one end, that passes just through the cork in the 

 flask, has an internal diameter of 7 mm., is cut ofi' oblique- 

 ly, and bent so that, on inclining the whole apparatus 

 when put together, the acid can be made to flow from the 

 bulb into the flask ; the other end of this tube is turned 



