As is seen from the above description the method is essentially a reduction process by the action of a powerful deoxidizer in the presence of an alkali. The crystals of the thiosulfate salt cannot be brought into direct contact with a pure alkali, like soda or potash, without forming at once a wet mass which would tend to cake and obstruct the tube. The soda-lime is therefore a mechanical device to prevent this fusion. Where many analyses are to be made an iron tube, for economical reasons, may be substituted for the glass; but the glass tube permits a more intelligent observation of the progress of the analysis. Since charcoal has very high absorbent powers it will be found always to contain a little nitrogen which may be in a form to generate ammonia during the combustion. The charcoal used should therefore be previously boiled with caustic soda or potash solution, dried, powdered, and preserved in well-stoppered bottles. Although pure sugar is practically free of nitrogen, even when it is used, it is advisable to occasionally make a blank determination and thus ascertain the correction to be made for possible contamination. =177. Boyer’s Modification of Ruffle’s Method.=—The principle of the method rests on the observation that if nitrates be heated in a combustion tube with calcium oxalate and soda-lime, not more than two-thirds of the total nitrogen appear as ammonia; but if a certain proportion of sulfur be added the whole of the nitrogen is recovered.[23] The process may be divided into two reactions; _viz._: (1) Action of the calcium oxalate upon the sodium nitrate in presence of soda-lime: (2) The action of sulfurous acid and of calcium oxalate upon the sodium nitrate in presence of soda-lime. The analysis is conducted as follows: Dry and pulverize one-half gram of nitrate (Na or K) and mix it intimately with fifty grams of the reducing compound containing approximately ten per cent sulfur, 22.5 per cent neutral calcium oxalate, and 67.5 per cent soda-lime. The combustion tube is charged as follows: Length of tube fifty-five centimeters: Diameter of tube seventeen millimeters: Add first two grams pulverized calcium oxalate: Add next ten grams pulverized soda-lime: “ “ ten grams of the reducing compound: “ “ the nitrate incorporated with fifty grams of the reducing mixture: Add next ten grams of the reducing mixture: “ “ ten grams pulverized soda-lime: The tube is then lightly closed with an asbestos plug. The tube is heated gradually from the front backwards, the calcium oxalate furnishing finally the gas necessary to drive out the last traces of ammonia. The process is equally applicable to the determination of nitrogen in all its forms or to mixtures thereof.