84 CHEMICAL EXAMINATION 



matter is washed with a few cubic centimetres of water into a 

 100 c.cm. flask and 0.5 grm. dry calcium chloride added. After 

 the addition of a few drops of phenolphthalein, a 10 per cent 

 solution of caustic soda is added until a faint pink colour per- 

 sists and finally 25 c.cms. of lime water. The object of this is 

 to precipitate the phosphates as calcium phosphate. Make up 

 the volume to 100 corns., mix thoroughly and filter through a 

 dry paper. To 50 c.cms. of the filtrate add N. sulphuric acid 

 until just colourless, then add a few drops methyl orange and 

 continue the titration untU the yellow colour changes to pink. 



N 



— soda is now added until the reaction is just alkaline and the 



Uquid boiled to expel the carbonic acid liberated. The solu- 

 tion is cooled, a few drops of phenolphthalein solution and 

 sufficient neutral glycerine to amount to 40 per cent of the total 



N 

 volume is added. The solution is finally titrated with — soda 



imtil a permanent pink colouration is produced. Each cubic 



N 

 centimetre of — soda equals 0.0062 grm. of boric acid. 



Benzoic Acid. The proteids are precipitated by the addi- 

 tion of 5 c.cms. of dilute hydrochloric acid and shaking: then 

 shake with several portions of ether, taking care to avoid the 

 formation of an emulsion. If this should occur, resort must be 

 made to a centrifuge in order to separate it. The ethereal 

 extract containing the benzoic acid and fat is shaken with water, 

 rendered alkaUne by the addition of ammonia, and the aqueous 

 extract evaporated nearly to dryness. After aU the ammonia 

 has disappeared, a few drops of ferric chloride are added and 

 the presence of benzoic acid is indicated by the formation of a 

 flesh-coloured precipitate. If any ammonia is left in the solu- 

 tion, a reddish-brown precipitate of ferric hydrate is obtained, 

 so that it is essential that all traces of this disturbing sub- 

 stance are removed before applying the final test. 



Salicylic Acid. This is detected in exactly the same manner 

 as is described above for the detection of benzoic acid. On addi 



