It is seen from the above that the nitrate will give, by this treatment, double the volume of nitrogen which it contains. In practice, the two reactions may be secured in one operation by warming the nitrate solution slowly with sulfuric and phosphorous acids and ammonium chlorid. The nitric acid, as it becomes free, gives a part of its oxygen to the phosphorous compound, and the nitrous acid, in a nascent state, is at once reduced by the ammonium chlorid. There are two sources of error which must be guarded against in the work; a portion of the nitrogen may escape reduction to the elementary state, or some of the nitrate may fail to be decomposed. These errors are easily avoided if the reaction be begun slowly, so that the evolution of gas may be gradual. The temperatures at first should, therefore, be kept as low as possible. The development of red fumes, showing the presence of undecomposed nitrogen oxids, shows that the results will be too low. It is necessary, also, to provide for the absorption of the hydrochloric acid which is formed. The reaction is very conveniently conducted in the apparatus shown in Fig. 16. The decomposition takes place in the flask A and the mixed gases pass into the absorption bulb C. The delivery-tube is very much expanded, as shown in the figure, so that no soda-lye can enter A during the cooling of the flask. The absorption bulb is connected with A and B by the tubes a and b as shown. The tube d connects the apparatus with the gasvolumeter.[181] The bulb B serves as a pipette for the introduction of the decomposing acid. The operation is conducted as follows: Three cubic centimeters of the nitrate solution, containing no more than 300 milligrams of substance, are placed in the flask A with half a gram each of crystallized ammonium chlorid and phosphorous acid. In the bulb B are placed seven cubic centimeters of sulfuric acid to which has been added one-third its volume of water. Two cubic centimeters of acid are allowed to flow from B into A. The apparatus is brought to a constant temperature by being immersed in a large cylinder, E, containing water at a temperature which can easily be controlled. When this constant temperature has been reached the apparatus is taken from the cooling cylinder which contains also a smaller cylinder, D, nearly filled with water and connected through f′ with the measuring apparatus M. The barometer-tube F is half filled with colored water so that the pressure may be equalized before and after the operation. The flask A is warmed very gently at first, and the nitrogen evolved is conducted into D driving an equivalent volume of water into M. The evolution of the gas must be carefully controlled and the heat at once removed if it become too rapid. The appearance of a red color shows the evolution of oxids of nitrogen rendering the analysis inexact. When the evolution of nitrogen has nearly ceased the lamp is removed and some more sulfuric