800 



ORGANIC ANALYSIS. 



its own bulk of carbonic acid at the observed 

 temperature and pressure, we must in our cal- 

 culations add the bulk of the liquid to that of 

 the gas actually observed. Having reduced 

 the bulk of gas to the standard pressure of 30 

 inches and the temperature of 60 F., accord- 

 ing to the rules given in all works on physics, 

 we deduce the quantity of sugar, since 100 

 cubic inches of carbonic acid are furnished 

 by the decomposition of 106'6 grs. of grape 

 sugar. 



If mercury be not at hand, we may, by 

 adapting a tube containing chloride of cal- 

 cium, and a bulb apparatus charged with 

 strong solution of potash,* the weight of which 

 is accurately known, to a tubulated retort, ob- 

 tain a result of considerable accuracy. In a 

 half-pint retort, so adjusted, 500 grs. of urine 

 are placed, and 30 or 40 grs. of yeast added ; 

 through the tubulure of the retort a straight 

 tube passes, and dips below the surface of the 

 fluid; the upper extremity is closed by a cork. 

 It is set aside to ferment at a temperature of 

 70 ; the chloride of calcium retains the mois- 

 ture, and the potash ley absorbs the carbonic 

 acid ; by the increase of weight we know the 

 quantity of carbonic acid formed. As at the 

 close of the experiment the apparatus will be 

 full of carbonic acid, it must be displaced by re- 

 moving the cork from the straight tube passing 

 through the tubulure of the retort, and then 

 gently drawing air through the apparatus for 

 some minutes by careful suction at the extre- 

 mity of the potash apparatus, in the manner 

 to be described presently when treating of the 

 process of ultimate analysis. 100 grs. of car- 

 bonic acid indicate 225 grs. of diabetic sugar. 



Another method of ascertaining the quantity 

 of sugar consists in adding to a given quantity 

 of the fluid a known weight of yeast having 

 by experiment determined the quantity of fixed 

 matter contained both in the yeast and in the 

 fluid operated on. After fermentation is com- 

 plete the solution is evaporated to dryness, and 

 the loss of solid matter sustained indicates the 

 quantity of sugar which has passed oft' as alcohol 

 and carbonic acid ; the urea likewise is de- 

 stroyed in the process, and its quantity must be 

 deducted from the total loss. It is very desi- 

 rable when sugar is present in considerable 

 quantity that the evaporation to dryness should 

 be performed in vacuo over sulphuric acid, as 

 it is the only method that ensures our ob- 

 taining the sugar always in the same state of 

 hydration. This process, however, is tedious, 

 always requiring many days for its completion : 

 some comparative experiments, showing the 

 value of this precaution, will be detailed here- 

 after. 



Our methods of exactly determining the 

 quantity of sugar of milk are imperfect; I 

 shall describe the plan which answers best 

 when treating of the analysis of milk. 



Uric acid. This is one of the most inte- 

 resting and important animal products from the 



* These pieces of apparatus will be described in 

 detail in the directions for the performance of ulti- 

 mate analysis. 



part it frequently performs in some of the most 

 serious and distressing diseases to which we are 

 liable. The method of detecting its presence 

 by evaporation on glass with nitric acid has 

 already been described. When no albuminous 

 principles are present, the solution is evaporated 

 to dryness and the residue treated with water, 

 acidulated with hydrochloric acid; the inso- 

 luble portion is dried and weighed, then 

 burned ; the weight of the remaining ash 

 (silica), if any, is deducted ; the loss indicates 

 the quantity of uric acid. 



Urobenzoic, or, as it is often called, hippuric 

 acid, has hitherto been found only in the urine, 

 in which it generally exists in minute quantity, 

 according to Liebig. Its quantity may be as- 

 certained by adding hydrochloric acid to the 

 liquid concentrated by evaporation. It is eva- 

 porated to dryness by a water heat, and the 

 residue digested with pure anhydrous ether as 

 long as any thing is dissolved. By sponta- 

 neous evaporation it is left behind nearly pure, 

 and may be weighed ; traces of urea crystallize 

 with it, and a little of the odorous principle, 

 which obstinately adheres to it. If the ether 

 have dissolved any fatty matter, the addition of 

 boiling water will dissolve the acid and leave 

 the fats. Urobenzoic acid may be detected by 

 heating a crystal in a test tube ; benzoic acid 

 and benzoate of ammonia, and a few red drops 

 of an oily matter, sublime, accompanied by a 

 smell of bitter almonds and of the Tonka bean. 

 Alcohol dissolves it freely, and the solution by 

 evaporation leaves stellated groups of needle- 

 shaped crystals. With perchloride of iron 

 solutions of the urobenzoales furnish a cinna- 

 mon brown precipitate. 



Lactic acid cannot be quantitatively deter- 

 mined without difficulty. The best method 

 is as follows: The solution if acid is neu- 

 tralized with ammonia, evaporated to dryness, 

 and the residue exhausted with alcohol; to 

 the filtered liquid sulphuric acid is added drop 

 by drop as long as a precipitate ensues; the 

 bases are thus removed as sulphates. The solu- 

 tion is filtered and the precipitate washed with 

 alcohol; the clear liquid is digested with fre- 

 quent agitation, at a moderate heat, for twenty- 

 four hours, with carbonate of lead : hydrochloric, 

 sulphuric, and phosphoric acids are thus sepa- 

 rated as insoluble salts, while lactate of lead dis- 

 solves. The solution is a second time filtered, 

 sulphuretted hydrogen gas transmitted through 

 the clear liquid, and the sulphuret of lead sepa- 

 rated by another filtration ; the filtered fluid is 

 evaporated to dryness to expel the alcohol and ex- 

 cess of gas, the residue redissolved in water and 

 digested with carbonate of zinc ; by evaporation 

 of the filtered liquid crystals of lactate of zinc 

 are obtained. If the solution is now mixed 

 with carbonate of potash in excess, evaporated 

 to dryness, exhausted with boiling water and 

 the residue dried and ignited, pure oxide of 

 zinc is obtained: 100 grs. of this oxide indicate 

 202. 5 grs. of lactic acid. 



If oxalic acid be suspected in any liquid, it 

 must be super-saturated with lime water. On 

 treating the precipitate with acetic acid the 

 phosphates dissolve, and oxalate of lime re* 



