If the solution be pure, the percentage of ammonia present may be determined by reference to a table of specific gravities.
When neutralizing the solution with an acid, it is safest, if the solution be strong, to dilute with water, so as to avoid a loss of gas from the beating which takes place when an acid is added, the acid used in titrating should consequently be somewhat dilute; from the number of e.e. of standardized acid (sulphuric or hydrochloric) required to neutralize the solution, the amount of ammonia can be at once determined.
As a control, if the solution contained ammonia only, and hydrochloric acid has been used, the mixture should be evaporated to dryness on the water bath, and dried at 100°, until the weight is constant, or at least, until the loss becomes very slight. This will also furnish a test for the strength of the acid. The amount of the alkali contained in the carbonates and bicarbonates or their mixtures may be determined in the same way.
100 parts of ammonium chloride contain ;— Ammonium NH, 33.72 Ammonia . . . 31.83 Chlorine Cl. 66.28 or Hydrochloric Acid HCI. 100 • 00 100 • 00 Sulphate of ammonia, not being so stable on drying as the chloride, indicates the non-suitability of sulphurio acid for the estimation of ammonia gravimetrically.
As the carbonates of ammonia when heated in solution are decomposed, the methods given for the volumetric determination of the carbonic acid contained in a sample of this salt require care in their application, and can scarcely be recommended.
A solution of chloride of barium is added to the hot solution of the ammonia carbonates, and the precipitated carbonate of baryta collected on a filter and well washed. The carbonate of baryta is then dissolved in a measured quantity of standard acid, winch must be in excess, and the excess of acid carefully titrated with a solution of standard alkali. A much simpler method is to determine the loss direct of carbonic acid, when a weighed quantity is decomposed with hydrochloric acid in any of the ordinary forms of carbonic acid apparatus.
Combined ammonia requires a different treatment. When the ammonia can be expelled from its combinations by means of soda, potash, or lime, the salt is boiled in a flask with a solution, preferably, of caustic soda or potash ; the liberated ammonia is collected in a receiver containing a measured quantity, in excess, of hydrochloric acid, and after the decomposition and absorption of the gas is completed, the excess of acid is titrated. 'As, however, the fumes of
chloride may return to the evolution flask, and become again decomposed, it is evident that inaccu racies may occur. The apparatus is shown in Fig. 202, in which G is the generating flask, L a Liebig's condenser, C the condensing flask, and T a tower in which the vapours escaping through C are condensed. This method is suitable for estimating the ammonia in "gas liquor," which contains both free and combined ammonia, to ascertain how much exists in each of these conditions, the distillation is first carried on without the addition of potash or soda, until all the free ammonia has passed over ; the contents of the retort are allowed to cool, and the receiver charged with acid as before. On the addition of caustic potash or soda to the contents of the retort and renewed heating, the combined ammonia is decomposed, the liberated ammonia passing over into the receiver. The results, which are only approximately correct, since many salts volatile at 100° may be present, will furnish a far better idea of the alkalimetrical value of a sample of gas liquor than can be obtained from its specific gravity. The determination of ammonia or ammonia salts iu the juices, leaves, or stalks of plants is generally made in the same way. It is, however, important to bear in mind that the caustic alkalies may, by acting on other nitrogenized substances contained in the plant, generate ammonia ; thus, in the case of tobacco or snuff, where the excise regulation fixes the percentage of alkaline salts which may be present, we must guard against the reduction of nitrates, and remove by means of ether, alcohol, &c., those principles which may generate ammonia when heated in a free state, such as nicotine. Hydrate of magnesia may be employed in such cases instead of the alkalies, since it does not act on the nitrogenous principles present, but liberates the ammonia only.