gram of the salt in 100 c. c. of water. The washing l>y decantation is performed by 

 adding the hot mixture in small quantities at a time, and heating up the precipitate 

 well with a thin glass rod after each addition. The pump is kept in action all the 

 time, but to keep out dust during the washing the cover is only removed from the 

 crucible when the fluid is to he added. 



Put the capsule and precipitate aside, return the washings once through the 

 ashestos so as to obtain them quite clear, remove them from the filter and set aside 

 to recover excess of silver. Rinse the receiver and complete the washing of the 

 precipitate with about 200 c. c. of cold water. Half of this is used to wash by 

 decantation, and the remainder to transfer the precipitate to the crucible with the 

 aid of a trimmed feather. Finish washing in the crucible, the lumps of silver 

 chlorid being broken down with the glass rod. Remove the second filtrate from the 

 receiver and pass about 20 c. c. of 98 per cent alcohol through the precipitate. Dry 

 at 140" to 150. Exposure for half an hour is found more than sufficient, at this 

 temperature, to dry the precipitate thoroughly. 



Or (&) standard sulphuric acid the absolute strength of which has been deter- 

 mined by precipitation with barium chlorid and weighing the resulting barium 

 sulphate. 



For ordinary work half normal acid is recommended, i. e., acid containing 18.2285 

 grams of hydrochloric acid or 24.5185 grams sulphuric acid to the liter; for work in 

 determining very small amounts of nitrogen, one-tenth normal acid is recommended. 

 In titrating mineral acids against ammonia solutions, use cochineal as indicator. 



(2) Standard alkali, the strength of which, relative to the acid, has been accurately 

 determined. One-tenth normal ammonia solution, i. e., containing 1.7051 grams of 

 ammonia to the liter, is recommended for accurate work. 



(3) Sulphuric acid, specific gravity 1.84, free from nitrates and also from ammo, 

 nium sulphate, which is sometimes added in the process of manufacture to destroy 

 oxids of nitrogen. 



(4) Metallic mercury or mercuric oxid, prepared in the wet way. That prepared 

 from mercuric nitrate can not be safely used. 



(5) Potassium permanganate finely pulverized. 



(6) Granulated zinc, pumice stone, or 0.5 gram of zinc dust is to be added to the 

 contents of the flasks in distillation, when found necessary, in order to prevent 

 bumping. 



(7) Potassium sulphid. A solution of 40 grams of commercial potassium sulphid in 

 1 liter of water. 



(8) Soda. A saturated solution of sodium hydrate free from nitrates. 



(9) Indicator. Solution of cochineal prepared as follows: Tincture of cochineal is 

 prepared by digesting and frequently agitating 3 grams of pulverized cochineal in 

 a mixture of 50 c. c. of strong alcohol with 200 c. c. of distilled water, at ordinary 

 temperatures, for a day or two. The solution is decanted or filtered through 

 Swedish paper. 



APPARATUS. 



(1) Kjeldahl digestion flasks of hard, moderately thick, well-annealed glass. These 

 flasks are about 22 cm. long, with a round, pear-shaped bottom, having a maximum 

 diameter of 6 cm., and tapering out gradually in a long neck, which is 2 cm. in 

 diameter at the narrowest part, and flared a little at the edge. The total capacity 

 is 225 to 250 c. c. 



(2) Distillation flaslcs of ordinary shape, of 550 c. c. capacity, or preferably flasks of 

 the same capacity of well-annealed glass and of pear-shaped bottom, for both diges- 

 tion and distillation, fitted with a rubber stopper and a bulb tube above to prevent 

 the possibility of sodium hydrate being carried over mechanically during distillation. 

 The bulbs are about 3 cm. in diameter, the tubes being of the same diameter as the 

 condenser and cut off obliquely at the lower end. The bulb tube is adjusted to the 

 condenser by a rubber connection. 



