. The analysis of food and drugs . ably about 155° C. Standard Ammonia Solution.—The standard solution ofammonia generally employed is made up so that 1 contain 00001 gramme of ammonia; the saltgenerally used is ammonium chloride (NH^Cl). If weweigh out 315 grammes of the pure salt, and dissolve thisin a litre of water, this will form a convenient stock solutionfrom which to prepare an ammonia standard containing•00001 gramme of ammonia per , which we do by taking10 of the strong solution and diluting it to 1000 distilled water. It is hardly needful to say that thewa
. The analysis of food and drugs . ably about 155° C. Standard Ammonia Solution.—The standard solution ofammonia generally employed is made up so that 1 contain 00001 gramme of ammonia; the saltgenerally used is ammonium chloride (NH^Cl). If weweigh out 315 grammes of the pure salt, and dissolve thisin a litre of water, this will form a convenient stock solutionfrom which to prepare an ammonia standard containing•00001 gramme of ammonia per , which we do by taking10 of the strong solution and diluting it to 1000 distilled water. It is hardly needful to say that thewater used to make up these solutions must be ammonia- 60 CHEMICAL AND BIOLOGICAL ANALYSIS OF WATER free. The following calculation shows why 315 grammesof ammonia salt are employed: — NH4CI = 535, NH3 = 17,.*. 1 gramme NHg is contained in 315 grammes NH4CI. Preparation of Nesslers Reagent.—Nesslers solution con-sists of a solution of mercuric iodide and potassium iodide,and is prepared by dissolving 35 grammes of potassium. Apparatus foe Watbk Distillation. iodide in about 100 of distilled water, and then addingto it a cold solution of 16 grammes of mercuric chloride dis-solved in about 300 of distilled water, when it will befound that a slight permanent precipitate is produced. Themixture is then made up to 1000 by the addition of 20 percent, caustic potash solution. Even after the solution hasbeen allowed to stand at rest for some weeks, and the clear CHEMICAL EXAMINATION 61 liquid drawn off, it will still continue to deposit a yellowishsediment; but this need cause no trouble if it is not stirredup by inserting the pipette right to the bottom of thebottle. The danger of sucking up the liquid, which isexceedingly unpleasant to taste, may be avoided by fittinginto a rubber cork a pipette with its bulb at the end. Asthe bulb is constantly immersed in the solution, the requiredamount can be retained by simply placing the finger on thefree end. If a long na
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