EXPERIMENT STATION. 113 



No fumes or tarry matters, indicative of incomplete combustion, 

 should appear in the bulh containing standard acid. 



When the combustion proper is begun it may be carried on 

 quite rapidly until completed. 



The tube is cooled below a red heat befoi-e aspirating. 



The ammonia from the combustion is received in standard 

 hydrochloric acid and titrated with a standard ammonia solution, 

 using tincture of cochineal as an indicator. 



The advantages of using cochineal tincture instead of litums solu- 

 tion are very considerable. It can be kept unaltered indefinitely, 

 as litmus cannot, it is not sei'iously afiected by the presence ot 

 carbonic acid in solutions, and as an indicator it is more sensitive. » 



In our use of the mixture of slaked lime and sodium carbonate, 

 the acid in the bulb-tube is frequently colored more or less deeply 

 red. This in nowise interferes with the alkalimetry, for the red 

 color fades as the point of neutralization is reached. In burning 

 with simple slaked lime, the standard acid has almost invariably 

 remained colorless, a fact which shows that the combustion with 

 the latter is more perfect. Evidently it is highly heated water 

 vapor which at once oxidizes the carbon and hydrogeuizes the 

 nitrogen, and the slaked lime alone, operates more effectually 

 because it supplies more water in a given bulk of charge. 



As was to be anticipated, the lime, at the full red heat to which 

 it must be exposed, does not retain all the carbon dioxide that is 

 formed ; the gases which pass the standard acid give a copious 

 precipitate in baryta-water. The standard acid, however, takes 

 up from the heated gases too little carbon dioxide to sensibly 

 affect the point of neutralization, and the entire accuracy of the 

 determination is in no degree impaired. 



The contents of the tube, after the combustion is finished, are 

 mostly quicklime with some carbonate, since they slake strongly 

 and effervesce slightly in dilute acid. 



The following are some of the results obtained by the two 

 methods. Soda lime here signifies the mixture of about equal 

 bulks of sodium carbonate and slaked lime. The combustions, 

 have been executed by Mr, E. H. Farrington. 



