=214. The Halle Zinc-Iron Method.=—For determining the nitrogen in Chile saltpeter the reduction method is conducted at the Halle Station as follows:[179] Ten grams of the nitrate are dissolved in one liter and fifty cubic centimeters of the solution corresponding to half a gram of the sample, taken for each determination. The apparatus employed is shown in Fig. 15. A mixture of five grams of zinc dust and an equal weight of iron filings is employed as the source of hydrogen. The reduction takes place in an alkaline medium secured by adding to the other materials mentioned, eighty cubic centimeters of soda-lye of 1.30 specific gravity. The respective quantities of iron and zinc may be measured instead of weighed, as exact proportions are not required. After the addition of all the materials the flask is allowed to stand for an hour at room temperature. The distillation is then commenced and continued until at least 100 cubic centimeters of distillate have been collected. The receiving flasks are ordinary erlenmeyers, each of which contains twenty cubic centimeters of set sulfuric acid, as in the usual kjeldahl process. The flasks are sealed with a few drops of water by the device shown in the figure. After the end of the operation the water in each one is washed back into its proper flask with freshly boiled water. During the vigorous evolution of hydrogen, at the beginning of the operation, some kind of a safety arrangement is necessary to prevent the particles of soda-lye being carried over by the bubbles of that gas. The siphon bulb shown in the figure is found effective for this purpose. In this operation better results are obtained by condensing the escaping steam, and for this reason the block tin tubes are conducted through a tank supplied with a current of cold water. The ends of the tubes should not dip below the surface of the liquid in the receivers. When the condensed liquid collects in considerable quantities in the safety tube the lamp should be extinguished under the flask, which permits the return of the liquid to the flask by means of the siphon. This should be done two or three times during the progress of the distillation to prevent a too high concentration of the soda-lye, thus endangering the flask. The excess of the acid in the receiver is determined by titration, as in the regular kjeldahl method. Blank determinations should be made, from time to time, and corrections made in harmony therewith. =215. Method of the French Sugar Chemists.=—The nitrogen in Chile saltpeter is estimated by the French chemists according to the method of Schlösing, described in the first volume, page 500. In order to avoid the trouble of calculating the results from the volume of nitric oxid obtained, a determination is first made with a pure salt, sodium or potassium nitrate. The volume of gas obtained is read directly without correction and taken for direct comparison. The comparison is made as follows: