96 PROXIMATE ANALYSIS OF 



be distinguished. The soaps which have been formed must 

 be decomposed by hydrochloric acid. If, on the addition of 

 the acid, a smell of rancid butter is developed, then butyric, 

 and also capric and caproic acids are present. The vari- 

 ations in their melting points vrill enable us to determine 

 approximately the proportions of oleic, margaric, and stearic 

 acids. 



6. The residue not taken up by ether, must be treated 

 with anhydrous alcohol, which will take up the following 

 substances : salts of the fatty acids, especially soda-salts, as 

 well as any fat that had escaped the action of the ether, 

 also urea, bilin and the acids of the bile, biliverdin, alcohol- 

 extract, hffimaphsein, acetates, and lactates, a class of substances 

 which it is by no means easy to distinguish, and is still more 

 difficult to isolate. If a spirituous solution of chloride of 

 barium be added to the alcoholic solution, and a green precipi- 

 tate is thrown down, then biliverdin is present ; we may also 

 calculate with tolerable certainty (especially if the alcoholic 

 solution has a bitter, bilious taste) on the presence of bilin, 

 and the acids of the bile. An alcoholic solution of sulphuric 

 acid must now be added to the alcohol-solution that we are 

 testing, as long as any sulphates are precijntated. The solution 

 must now be filtered, and the alcohol, which still has an acid 

 reaction if any acetates are present, must be removed by dis- 

 tillation. On treating the residue with water, the fatty acids, 

 if they existed in combination with saline bases, will remain 

 undissolved, and must be removed by filtration. A portion 

 of this watery solution must be evaporated to the consistence 

 of a syrup, and allowed to cool; if, on the addition of an 

 excess of nitric acid, there are formed, either at once or after 

 some time, leafy or stellar crystalline groups, then urea is 

 present. Another portion must be treated with dilute sul- 

 phuric acid, and allowed to digest for some time. If bilin, 

 and the products of its metamorphosis, are present, a viscid or 

 oily acid, (insoluble in the acid fluid,) and a precipitate of an 

 extremely unpleasant bitter taste, are formed. The fluid sepa- 

 rated fi'om these substances must be digested with pounded 

 marble, or (which is better) with carbonate of baryta, in order 

 to remove the sulphvu'ic acid. It must then be boiled with 

 carbonate of zinc ; if it contain lactic acid, crystals of lactate 



