DETECTION OF SUBSTANCES. [CH. XIV. 



4. Note the reaction to litmus. An acid reaction excludes 

 the presence of mucin, nucleoproteins, caseinogen, and usually 

 earthy phosphates. 



5. If acid test for free HC1 by Gunsberg's test. (Ex. 246.) 



6. Sprinkle some flowers of sulphur on the surface of a portion 

 of the fluid in a test-tube. If the particles fall through the surface, 

 bile salts are probably present. (Ex. 316.) Confirm by Petten- 

 kofer's test. (Ex. 315.) 



7. If the fluid be brown or green, apply the Huppert-Cole test 

 (Ex. 318) for bile pigments. 



8. If the fluid be red or brown, examine for blood-pigments 

 or derivatives by Table F, page 366. 



9. If there are any reasons for suspecting the presence of 

 ferments, examine as directed on page 367. If none of the colour 

 reactions for proteins are obtained, ferments are probably absent. 



10. Examine for proteins by Millon's and the biuret reactions 

 (Ex. 22 and 24). If they be present, proceed as directed in Table 

 A, B or C, according to the reaction of the fluid. 



11. If proteins are absent, proceed to Table E. 



12. Test for uric acid if the fluid be alkaline, neutral or only 

 faintly acid. Acidify with a drop or two of strong hydrochloric 

 acid; uric acid may separate out as a crystalline powder. Make 

 another portion of the solution alkaline with ammonia, saturate 

 with NH 4 C1 and apply the murexide reaction to the precipitate thus 

 obtained. (Ex. 352.) 



13. If the fluid be alkaline, treat a little with a solution of 

 calcium chloride. A white curdy precipitate indicates the presence 

 of soaps. (Their presence should be confirmed by the methods 

 given in Ex. 177.) 



14. Treat a portion with a little hypobromite solution. If an 

 effervescence is obtained, test for urea by Ex. 343. If this is 

 negative the solution may contain ammo-acids or ammonium salts. 

 The bromine test for free tryptophane (p. 217) may give a valuable 

 indication. 



