294 



On Chemical Tests. 



[Oct. 



/. Mercury also gives a white precipitate with sulphuric acid, which 

 becomes yellow when boiled. But there are other more useful tests 

 for mercury, see 82. 



g. Carbonic acid is discovered by its effervescence on adding sul- 

 phuric acid, in the same manne t r as before mentioned under the head of 

 muriatic acid. 



h. When water containing vegetable or carbonaceous matter is eva- 

 porated after adding sulphuric acid, it acquires a distinct brown colour, 

 which becomes deeper as the liquid becomes more concentrated. 



19. ACID iartaric distinguishes potash from soda. The solution 

 must be concentrated, and the tartaric acid be added in excess. With 

 potash it produces a precipitate of bi-tartrate of potash, or cream of 

 tartar; with soda it produces no precipitate. 



a, To detect tartaric acid ; add to a solution which must be concen- 

 trated an excess of lime water, and a precipitate will be formed which 

 is soluble in a small quantity of ammonia : — or add carbonate of potash 

 which will precipitate tartrate of potash, or cream of tartar. 



20. ACID uric, see 13, d for its detection. 



21. ACIDS free, are detected by litmus o?\ turmeric paper, or by 

 tiiictures or solutions of litmus and turmeric ; but the litmus test is not 

 universally distinctive, see 77. Acids in combination with salts and other 

 bases, are discovered by a variety of tests, see ail the foregoing articles. 



22. ALBUMEN is detected by the per-muriate of mercury, see 

 53. It is also indicated by the muriates of gold, and tin ; by sub-ace- 

 tate of lead, and nitrate of silver ; but these tests are not decisive, as 

 they are affected by other substances, see 87. When a liquid contain- 

 ing albumen is submitted to galvanism (which is considered a most 

 delicate test) it coagulates on the wire connected with the positive pole 

 of the battery, and pure soda is found at the negative wire. 



a. The precipitate by the per-chloride of mercury is soluble in acetic 

 acid, and is not altered by boiiing. Sulphate of copper added to the 

 solution produces a green, and chloride of iron, a yellowish-brown pre- 

 cipitate. 



b. An excess of sulphate of copper completely precipitates albumen 

 of a green colour, which is dissolved by an excess of albumen. Am- 

 monia dissolves this precipitate forming a dark blue solution. Potash 

 produces a violet solution. A solution of carbonate of soda dissolves it 

 completely, occasioning a violet colour. Potash throws down the cop- i 

 per, but in the filtered liquor, no sulphuric acid can be detected. The 



