ORGANIC ANALYSIS. 



797 



This is evaporated to dryness in a water-bath. 

 It is carefully weighed and the total solid con- 

 tents determined ; the loss indicates volatile 

 matters consisting almost entirely of water. 

 The residue is carefully incinerated with the 

 usual precautions until all traces of carbon 

 are removed : on weighing again we obtain 

 the fixed saline constituents. 



By this means we have determined 



Water and volatile matters. 



Organic matters and ammoniacal salts. 



Fixed saline matters. 



The quantity of each organic substance has 

 now to be estimated. We have at present no 

 absolutely exact method of determining all the 

 ingredients from one portion only of a fluid ; 

 the following offers the nearest approximation. 



a. Fibrin separates by spontaneous coagula- 

 tion ; it is washed and determined in the manner 

 to be described hereafter. 



b. If casein and albumen be both present, a 

 given portion of the clear liquid is acidulated 

 with a few drops of acetic acid, and evaporated 

 to dryness in vacuo over sulphuric acid. The 

 residue is digested with successive portions of 

 water at 120, as long as any thing dissolves; 

 this residue is then dried upon a water-bath, 

 pulverised, and treated with ether, by which 

 all fatty matters are removed ; casein alone 

 remains behind. It is completely dried, weigh- 

 ed, incinerated, and the ashes deducted. This 

 method of separating the casein is imperfect, as 

 a portion of this substance generally redissolves 

 on the addition of water. If uric acid be pre- 

 sent, it will be found with the casein, which 

 must be dissolved in solution of potash, diluted, 

 filtered, supersaturated with acetic acid, by 

 which the azotised matter at first precipitated 

 is redissolved. Uric acid alone remains; it is 

 collected on a weighed filter, and the quantity 

 determined. It should always be tested by the 

 microscope or by nitric acid. 



c. The aqueous solution filtered from the 

 casein, or the liquid for examination, if this 

 principle be absent, is evaporated to dryness 

 by a water-bath. If much fat is present, the 

 residue is washed with ether to remove the 

 greater part of the oily matter, then dried tho- 

 roughly, and powdered ; an operation which, 

 after the preliminary treatment with ether, may 

 be effected without much difficulty. The pul- 

 verized mass is digested with ether, and the 

 ethereal solutions, including that in which the 

 casein was digested, are mingled and evapo- 

 rated to dryness. Cholesterin, fatty matters, 

 lactates, and a trace of urea are obtained; 

 by digesting with water the cholesterin and 

 fats alone remain and may be collected on a 

 filter and weighed. 



iL The residue, after digestion with ether, is 

 treated with boiling water; the solution thus 

 obtained may contain urea, sugar, sugar of 

 milk, extractive and saline matters, in short, 

 every thing except the albumen, which is com- 

 pletely dried and then weighed. When no 

 casein is present, the uric acid, if any, will 

 accompany the albumen, and may be separated 

 from it in the manner directed for its separation 

 from casein. 



e. The filtered liquid is evaporated to dry- 

 ness and treated with a mixture of one part of 

 anhydrous ether with two of absolute alcohol, 

 by which urea, muriate of ammonia, lactates, 

 the alcoholic extractive matters so called, and 

 a small part of the sugar, are dissolved. The 

 remainder of the sugar, sugar of milk, aqueous 

 extractive matters, urates, sulphates, chlorides, 

 and phosphates remain behind, forming re- 

 sidue (1). 



_/. The alcoholic solution is evaporated to 

 dryness and weighed: the solid matter divided 

 into two portions ; one is dissolved in water 

 acidulated with nitric acid, and treated with 

 nitrate of silver, by which the chlorine is sepa- 

 rated as chloride of silver, and hence the mu- 

 riate of ammonia is determined ; from the other 

 portion we determine the quantity of urea by 

 oxalic acid with the usual precautions. Having 

 thus determined the weight of the muriate of 

 ammonia and of the urea, we infer the defici- 

 ency to consist of a little sugar, lactates, and 

 alcoholic extract. 



g. The residue (1), which contains sugar, su- 

 gar of milk, watery extract, and salts, is boiled 

 with proof-spirit as long as any thing is dis- 

 solved ; the solution is evaporated to dryness, 

 and if grape sugar be present, half the residue 

 must be dissolved in water and fermented with 

 yeast to determine the proportion of this sub- 

 stance, and its weight is deducted from the 

 weight of the residue left on evaporating the 

 spirituous solution ; the other half residue is 

 incinerated, and the quantity of saline matter 

 ascertained; by deducting the weight of the 

 sugar and salts we then obtain that of the sugar 

 of milk, together with the alcoholic extract, 

 from which we possess no exact means of se- 

 parating it. It, however, very rarely happens 

 that in the same fluid we meet with grape 

 sugar and sugar of milk ; the absence of sugar 

 will obviously much simplify the method of 

 proceeding. 



h. The portion undissolved by proof-spirit 

 is dried and weighed ; it is incinerated and 

 again weighed; the difference between the two 

 weighings gives the quantity of watery extract. 



This will be the general plan of operations 

 if it be required to determine the quantity of 

 each individual ingredient. From the number 

 of operations required, and the destructible na- 

 ture of the ingredients, the result, as already 

 mentioned, is not rigidly accurate. Frequently, 

 however, it is merely necessary to ascertain the 

 proportion in which one substance only is 

 found; the presence or absence of others being 

 all that it is desired to know concerning them. 



We proceed now to the special consideration 

 of the different animal principles. 



Fibrin. Although the identity, in chemical 

 composition, of fibrin, albumen, and casein has 

 lately been strongly insisted on by Liebig and 

 his pupils ; yet, as in their physical properties 

 at least, and in the offices they perform in the 

 body, they differ considerably, it is frequently 

 of great importance to determine the relative 

 proportion of each in the fluids and secretions. 

 These three principles occur both in the coagu- 



