ADVANCED CHEMICAL PHYSIOLOGY 



299 



in chromogen form. Haematoporphyrin possesses a well-marked 

 spectrum which differs according to whether the preparation is acid or 

 alkaline (see pp. 247 and 250). It is impossible to detect haematopor- 

 phyrin spectroscopically in the urine unless it be present in fairly large 

 amount ; when present, even in acid urine, it is the alkaline spectrum 

 which is obtained. It may be obtained from the urine by adding to 

 each 100 c.c. urine 20 c.c. 10 per cent, caustic soda. The precipitate is 

 filtered off, washed, and then treated with acid alcohol. The solution 

 in acid alcohol gives the acid spectrum, if it be rendered alkaline the 

 alkaline spectrum. If the urine is rich in the pigment shaking with 

 acetic ether or amyl alcohol will extract it. If urobilin be also pre- 

 sent take off the acetic ether extract, acidify with acetic 

 acid and shake well with water. Urobilin passes over 

 into the water, leaving hsematoporphyrin. 



CHAPTER XIX 

 FATS 



Estimation of Fat by Soxhlet Method. The dried 

 material to be extracted, finely ground, is placed in 

 a suitable paper extraction thimble and placed in the 

 extraction chamber of the Soxhlet apparatus, which is 

 then connected with the flask, previously weighed, 

 below and the condenser above. After the addition of 

 the appropriate amount of ether, as anhydrous as pos- 

 sible, extraction is carried out, preferably on an electric 

 heater, for six to eight hours. The ether is distilled off 

 from the flask ; when the distillation is complete, add 

 about 1 c.c. absolute alcohol and then heat the flask for 

 a short period at 100 C. to dry the contents. Cool 

 and weigh. 



Another more simple method, applicable to many 

 substances, is given on p. 303. 



Separation of Saturated and Unsaturated Fatty Acids. 

 10 gms. of suet are saponified with 10 c.c. of 40 per 

 cent. NaOH with 40 c.c. 96 per cent, alcohol added. 

 After completion of saponification add a few drops of 

 phenolphthalein solution and then neutralise the solu- 

 tion by means of 10 per cent, acetic acid. The neutral- FIG. 201. 

 ised solution is then poured into 500 c.c. of a 2 per 

 cent, solution of neutral lead acetate contained in a litre flask. Boil, 

 a precipitate of lead soaps forms, cool under the tap and allow precipi- 

 tate to settle. Decant off as much as possible of the clear supernatant 

 fluid and then wash precipitate three times with about 150 c.c. of 

 warm water (50-60C.). Let the precipitate drain well and finally 

 remove last traces of water by means of filter paper. Place the dried 

 lead soaps in a flask, add 150 c.c. ether and heat under a reflux con- 

 denser for ten to fifteen minutes in a boiling waterbath. Allow to 

 cool and stand overnight. Filter ethereal solution and add to the 

 filtrate dilute HC1 (1:4) until a precipitate forms (usually requires 

 about 60 c.c. acid). The ethereal extract contains the lead salts of 



