ADVANCED CHEMICAL PHYSIOLOGY 303 



combined fatty acids, etc., even amounting to about one- third of the 

 total dry weight of the faeces. 



Carbohydrates. On hydrolysis faeces normally yield reducing 

 substances equivalent to from 0-5 to 2 gms. of glucose. Under certain 

 conditions the output of carbohydrate may be markedly increased. 



Where it is desired to get the faeces belonging to a definite period 

 of feeding a fairly accurate separation may be got by giving the patient 

 5 grin, of charcoal at the start and at the end of the feeding period. 



Quantitative Analyses. 'Except for the water content most of the 

 analyses may be carried out on faeces which has been dried on the 

 waterbath and then ground to a fine powder. 



Estimation of the Water Content and Ash. (a) Of the thoroughly 

 mixed fasces take about 3 gms. on a small watch glass, weigh exactly, 

 shake the fasces into a small weighed platinum crucible (a silica crucible 

 will serve), and again weigh the watch glass. The difference between 

 the two weighings gives the amount of faeces actually used. Dry the 

 faeces in the crucible at 110 in a hot-air oven to constant weight. The 

 difference between the dry and the wet weight gives the water content. 



(6) To find the amount of ash. Heat the crucible, at first gently, and 

 then complete the ashing with a strong flame. Cool and weigh. 



Estimation of Nitrogen by Kjeldahl Method. Take 2-3 gms. of 

 moist faeces weighed as above or about 0-5 grm. of the dried faeces and 

 place in a combustion flask with a small piece of copper foil and 20 c.c. 

 N-free H 2 SO 4 and heat till the solution is colourless (for details see 

 Analysis of Urine ). A globule of mercury may have to be added instead of 

 the copper as fasces, particularly if they contain much fat, are somewhat 

 difficult to combust completely. If mercury be used, before distillation 

 some sodium sulphide or hyposulphite must be added in order to break 

 up certain Hg.-N. compounds which are formed during combustion. 



Estimation Of Fat. This may either be done by using the Soxhlet 

 extraction apparatus or by grinding up the faeces with ether. 



(a) Soxhlet method. Take about 5 gms. dried faeces and extract for 

 six to eight hours in a Soxhlet apparatus with dry ether. Distil off the 

 ether in the previously weighed small Soxhlet flask. When the 

 distillation is finished add about 1 c.c. absolute alcohol to the flask 

 and dry at 100 C. Cool and weigh. The increase in weight of the 

 flask gives total extractable fatty substances. 



(6) A quicker method of estimating the fat content. 



(1) Take 1 gm. dried faeces, place in a mortar, rub up with 30 c.c. 

 ether, allow to settle, then decant ether through a fluted filter paper into 

 a weighed beaker or flask. Repeat this grinding process three times. 

 Wash the filter paper, remembering the edges, thoroughly with ether. 

 Distil off the ether in the flask on a hot plate or waterbath. When 

 distillation is completed add 1 c.c. absolute alcohol to flask and dry at 

 100 C. Cool and weigh. Increase in weight of flask gives total fat and 

 free fatty acids. 



(2) Now add to the flask containing the total fat and free fatty acids 

 50 c.c. of pure alcohol previously rendered slightly alkaline to phenol- 



N 

 phthalein by titration with ^ NaOH. Heat carefully until all the fat 



N 

 and fatty acids are completely dissolved, cool and titrate withy^ NaOH ; 



add a few drops more phenolphthalein as indicator if necessary. This 



