202 ANNUAL OF SCIENTIFIC DISCOVERY. 



(2) iodide of ethyl with (2) alcohol in a closed vessel at 100° C. 

 lor variable lengths of time ; the blue resulting from longest ex- 

 posure. 



Aniline green is produced from a solution of sulphate of rosan- 

 iline in dilute sulphuric acid and some aldehyde, which is heated 

 until its color has changed to dark-green. Addition of a solution 

 of hyposulphite of soda separates the color. 



When a salt of aniline in solution is exposed to the action of 

 certain oxidizers, as salts of copper, chlorate and bichromate of 

 potassa, it yields a black dye, of such deptli that ordinary gall or 

 madder blacks appear gray or green in comparison. The fastness 

 of this color, its resistance to the action of acids, alkalies, soaps, 

 and sunlight, render it of great importance to manufacturers, and 

 make it one of the great achievements of late years. — Druggists' 

 Circular, 



HOW TO TEST THE PURITY OF WATER. 



It is of importance to be able to test the quality of water, not 

 only when for special purposes absolutely pure water is required, 

 but even in cases w.here such purity is not requisite, it may be of 

 great interest to ascertain of what the impurities consist. 



Pure water must satisfy the following conditions. — 1. It must 

 have no residue whatever when evaporated in a clear porcelain 

 or platina dish. 



2. It must form no precipitate with a solution of nitrate of 

 silver, which would indicate common salt, some other chloride, or 

 h^'drochloric acid. 



3. It must not precipitate with a solution of chloride of barium, 

 which would indicate a sulphate or sulphuric acid. 



4. It must form no precipitate with oxalate of ammonia, as 

 this would indicate some soluble salt of lime. 



5. It must not assume any dark or other shade of color when 

 passing sulphuretted hydrogen gas through it, or mixing it with 

 the solution of a sulphide salt, as this would indicate the presence 

 of lead, iron, or some other metal. 



6. It must not become milky by the addition of lime-water, 

 or a clear solution of sugar of lead, as this would indicate carbonic 

 acid. 



7. It must not discolor by adding solutions of corrosive subli- 

 mate, or chloride of gold, or sulphate of zinc, which discoloring 

 would indicate the presence of organic substances. When boiling 

 water with chloride of gold, the least trace of organic matter will 

 reduce the gold, and color the water brown. 



Results of these tests. — 1. Almost all spring waters are found 

 to leave a residue upon evaporation. 



2. Common salt is found not only in most springs and rivers, 

 but even in rain-water, many miles inland, when the wind blows 

 from the ocean. 



3. Sulphuric acid and sulphates are found in many springs; 



