37O DETECTION OF SUBSTANCES [CH. XIV. 



B. Solids. 



1. Examine a little microscopically, both dry and with the 

 addition of a drop of water. Look for starch grains, crystals of 

 urea, uric acid, urates, leucine, tyrosine, cholesterol, and haemin 

 scales. 



2. Heat a small amount of the solid in a dry tube, at first 

 gently and then more strongly. 



(a) If sublimation take place and an odour of amylamine be 

 given off, leucine is present. 



(b) If sublimation take place and a strong smell of ammonia 

 be evolved, urea is indicated. 



(c) A smell of phenol and nitro-benzol indicates tyrosine. 



(d) A smell of burning feathers indicates proteins, gelatin, etc. 



(e) A smell of acrolein indicates fats. 



3. Boil some of the solid with a small amount of water in 

 a tube, cool under the tap and leave the test-tube in a beaker 

 of cold water for 10 minutes. If gelatin be present, the solution 

 will set to a jelly. (Starch, if present, may form a thick paste, 

 which may be confused with the clean jelly given by gelatin. If 

 the tube be subsequently placed in boiling water, gelatin becomes 

 quite limpid, whilst starch remains thick.) 



4. If the solid be of a dark brown or red colour, boil a portion 

 with dilute alkali, filter, heat the filtrate with Stokes' fluid or 

 ammonium sulphide, and examine for the spectrum of haemochro- 

 mogen. (Ex. 305.) If this be obtained, the solid contains dried 

 blood or haematin. Confirm by obtaining haemin crystals. (Ex. 

 309-) 



5. The table on the next page can be followed, but the method 

 adopted will depend on the indications obtained by preliminary 

 tests. It is advisable to test for starch before deciding on a plan of 

 operation. 



