ADVANCED CHEMICAL PHYSIOLOGY- 305 



and the phosphate precipitate has redissolved. If there has been any 

 iron in the ash, and faeces commonly contains small amounts of iron, 

 a small precipitate of iron phosphate may remain after the treatment 

 with acetic acid. This precipitate must, if it be present, be filtered off. 

 Heat the clear solution to boiling point, add excess of ammonium oxalate 

 (20 per cent, solution) until the precipitation of lime is complete. Allow 

 to settle completely (best by standing overnight). Filter off precipitate 

 through a 12 cm. Swedish filter paper, washing thoroughly with boiling 

 water. The calcium may be estimated either gravimetrically (a) or 

 by titration (6). 



(a) Ignite the dried filter paper and precipitate in a platinum or 

 silica capsule over a blowpipe until constant in weight. Weigh as CaO. 



(b) Pierce the damp filter paper on the funnel with a glass rod and 

 wash through the precipitate into the beaker originally used for the 

 precipitation with water. Next, in order to remove the last traces of 

 the precipitate from the paper, wash repeatedly with small quantities 

 of 1 in 10 H 2 SO 4 . Heat the beaker to about 75 C. and continue heating 



N 

 till the calcium oxalate is all dissolved. Titrate at once with y, 



potassium permanganate and calculate to CaO. 



N 

 1 c.c. -TT> permanganate solution = 0-0028 gm. CaO. 



Tests for " Occult " Blood. These tests are only of value when a 

 meat-free diet is taken. The benzidine and phenolphthalin tests are 

 very delicate when properly applied. The guaiac test although not so 

 sensitive is quite useful. 



(a) Guaiac Test. Stir up 5-10 gms. faeces in a mortar with water 

 until it forms a thick fluid. (If the faeces is rich in fat treatment with 

 ether should first be carried out. ) Add one-third of its volume of glacial 

 acetic acid and mix thoroughly. Pour about 10 c.c. into a test tube, 

 add an equal volume of ether and mix thoroughly. Allow ether to 

 separate (aid of a centrifuge is useful), collect in a test tube, add 10 drops 

 of about 1 per cent, guaiac solution and about 4 c.c. of 10 per cent, 

 hydrogen peroxide. The whole is shaken. Provided no pus has been 

 present the blue colour may be assumed to indicate blood. 



(6) Benzidine Test. Dissolve a knife point full of pure benzidine 

 (keep in a dark place) in 2-3 c.c. glacial acetic acid and add 2 c.c. 

 hydrogen peroxide. A small quantity of faeces is shaken up with a 

 little hot water and 2-3 c.c. added to the benzidine solution. If blood 

 be present a bluish or greenish colour develops in two or three minutes. 

 Delicacy is about 1 : 100,000. 



(c) Phenolphthalin Test. To a suspension of a small amount of 

 faeces in water (about 2 c.c.) add about 1 c.c. of the phenolphthalin 

 reagent. (Add 2 gms. phenolphthalein and 10 gms. of zinc dust to 

 100 c.c. 20 per cent, caustic soda. Heat the bright red solution carefully 

 until it has become slightly yellow in colour, i.e. until the phenol- 

 phthalein is reduced to phenolphthalin. Pour off supernatant fluid and 

 keep in the dark, adding a little liquid paraffin to prevent surface 

 oxidation.) Then add 1, at most 2, drops of 10 per cent, hydrogen 

 peroxide. A bright red colour will develop, due to reoxidation, if 

 blood be present. Delicacy is about 1 : 800,000. 



