458 DIGESTION. 



t of crucible and saliva 33.562 grra. 

 Weight of crucible alone 23.296 grin. 



10.266 = weight of saliva used. 



Evaporate the saliva to dryness either in the air-bath or over 

 a water-bath, but finish the desiccation in the air-bath. Cool 

 and weigh the crucible as before. The amount of solid residue 

 is determined in the same way as that of the saliva itself, 

 thus : 



Weight of crucible and dried residue 23.342 grm. 

 Weight of crucible alone 23.296 grm. 



Difference .046 grm. =weight 



of residue. 



The amount of water is found by subtracting the weight of 

 the solid residue from that of the saliva used, thus : 



Weight of saliva used 10.266 

 Weight of solid residue .046 



11X220 weight of water. 



Hence percentage of water = '"" = 99.5 and 



Percentage of solid residue = ^- Xl00 = 0.44 



10.2G(> 



* 75. Qualitative Investigation of Inorganic Con- 

 stituents. For this purpose the saliva must be filtered so 

 as to separate the epithelium and mucus. It contains carbo- 

 nates, chlorides, phosphates and sulphates of potassium, 

 sodium, calcium, and magnesium, and in most cases also 

 potassium sulphocyanide. The presence of these several salts 

 may 1)0 demonstrated as follows : Carbonates. If a drop of 

 saliva is placed on an object-glass and covered in the usual 

 way, and a drop of acetic acid added, bubbles of gas will be 

 seen to form under the cover-glass. Chlorides. The saliva 

 is acidulated strongly with nitric acid, after which solution of 

 silver nitrate is added ; the precipitate formed is insoluble in 

 excess of acid, but dissolves readily in ammonia. Sulphates. 

 Tlu- turbidity produced by solution of barium, chloride, or 

 nitrate docs not disappear when nitric acid is added, and the 

 liquid is boiled. Pottn^nntm. If a little saliva is gently evapo- 

 rated ,, u a platinum wire and then heated in the flame of a 

 Bansen'fl lamp, the flame seen through blue glass exhibits a 

 violet i.olor. Sodium. Without the glass it presents the well- 

 known yellow color due to the presence of sodium. Calcium 

 may In- precipitated as oxalate by the addition of ammonium' 

 oxalate, Maym'tium as ammoniaco-magnesian phosphate. To 

 obtain the latter, ammonium chloride, and ammonia must first 



