ORGANIC ANALYSIS. 



803 



Sulphuric acid may be precipitated from the 

 filtered liquid or from any fluid suspected to 

 contain it by acidulating (if not already acid), 

 not too strongly, with nitric acid, and preci- 

 pitating with nitrate of baryta. The preci- 

 pitate should be well washed with boiling 

 water as long as any thing is dissolved, then 

 ignited and weighed. Boiling nitric acid is 

 without effect upon it; 100 grs. contain 34.19 

 of sulphuric acid. 



(B.) The insoluble portion consists of carbo- 

 nates and phosphates of the earths, and per- 

 haps of iron. We bring them into solution 

 by means of nitric acid, and supersaturate 

 with caustic ammonia to separate the phos- 

 phates; filter if necessary, and add oxalate of 

 ammonia; collect and ignite the precipitate, 

 moisten with solution of carbonate of am- 

 nionia; it is once more heated to incipient 

 redness, and it then consists of carbonate of 

 lime : the carbonic acid is estimated in the 

 manner already directed. The filtered liquid 

 is boiled with solution of carbonate of am- 

 monia; the magnesia, if any, precipitates and 

 must be strongly ignited; 100 parts indicate 

 110 of carbonic acid, which must be added to 

 that combined with the lime. 



Phosphoric acid. The quantitative estima- 

 tion of this body is attended with some dif- 

 ficulty, as it cannot be effected by direct pre- 

 cipitation, but is inferred from the loss. The 

 precipitate by caustic ammonia just obtained 

 consists entirely of earthy phosphates and phos- 

 phate of iron. It is ignited and the weight 

 ascertained. It is then brought into solution 

 by means of concentrated hydrochloric acid, and 

 ammonia added until the precipitate from the 

 still acid solution is no longer perfectly re- 

 dissolved. Acetic acid is now added and then 

 more ammonia, taking care that the liquid is 

 still strongly acid. Phosphate of iron alone 

 precipitates; this is separated by filtration, and 

 after strong ignition consists of 57.44 phos- 

 phoric acid and 42.56 sesquioxide of iron. 

 From the filtered liquid the lime and mag- 

 nesia are separated by oxalate of ammonia and 

 caustic ammonia, as will presently be de- 

 scribed ; then deducting the united weight of 

 the oxide of iron, lime, and magnesia from that 

 of the ignited mixed phosphates, the remainder 

 is phosphoric acid. 



In order to bring the tests for analogous 

 bodies together, I shall here interrupt the course 

 of the analysis to describe the methods of pro- 

 ceeding with those substances for which occa- 

 sionally, though more rarely, we have to look. 



Iodine, in organic fluids, always occurs in 

 the form of an iodide, and is not met with in 

 the human body in its normal condition. We 

 must evaporate to dry ness and treat the residue 

 with alcohol. The iodide will be dissolved ; 

 we again evaporate to dryness and re-dissolve 

 in water: (if the quantity be not very minute, 

 this preliminary process may be dispensed 

 with, merely concentrating the liquid and 

 allowing it to cool ;) iodine may now be 

 detected by adding a little cold solution of 

 starch, and pouring into the mixture a few 

 drops of solution either of chlorine or of chlo- 



ride of lime (bleaching liquor), when a blue 

 colour, more or less intense, is produced. The 

 quantitative estimation of iodine in these ana- 

 lyses is seldom required ; when it is, a neutral 

 solution of chloride of palladium is added to 

 the solution, accurately neutralized, and the 

 whole set aside in a warm place for twenty- 

 four hours, a black precipitate of iodide of pal- 

 ladium forms : it should be collected on a 

 weighed filter and dried at a very gentle heat, 

 otherwise part of the iodine escapes. 100 grs. 

 of iodide of palladium contain 70 of iodine. 

 By suspending this iodide in water and adding 

 starch and a little chlorine water, the blue 

 colour is produced as usual. 



Fluorine, when present, and it appears to be 

 a universal constituent of bones, is always in 

 exceedingly minute quantity. To discover it 

 we incinerate the dried matter, pulverize and 

 make it into a thin cream with oil of vitriol in 

 a shallow platinum crucible ; instead of its 

 usual cover the mouth is closed by a piece of 

 flat glass, the under surface of which has been 

 covered with a film of melted bees' wax or 

 some resinous varnish ; when firm or dry, a few 

 characters are traced with a sharp point to 

 expose the glass underneath ; the glass is 

 pressed upon the crucible so as completely to 

 close it, and the whole heated over a spirit- 

 lamp for a quarter of an hour. The glass 

 is kept cool by a piece of moistened paper. 

 If any fluorine be present, the traces upon the 

 glass from which the wax has been removed 

 will be more or less corroded ; the superfluous 

 wax may be removed by oil of turpentine, and 

 the corrosion may be rendered distinct by 

 rubbing a little powdered charcoal over the 

 surface. If any marks are produced, it is an 

 unequivocal proof of the presence of fluorine. 

 This method, however, is not very delicate. 



Free sulphur is detected by boiling the sub- 

 stance with solution of potash; if this element 

 be present in the unoxidized state, a black pre- 

 cipitate of sulphuret of lead is formed on add- 

 ing a few drops of acetate of lead. 



If we desire to know the quantity of free 

 sulphur, we first satisfy ourselves of the ab- 

 sence of sulphuric acid, or determine its quan- 

 tity accurately by the method already de- 

 scribed ; then deflagrate the substance or dry 

 residue with eight parts of pure nitre and two 

 of pure carbonate of potash,throwingthe mixture 

 in successive small portions into a platinum 

 crucible heated to redness ; the sulphur is thus 

 converted into sulphuric acid at the expense of 

 the oxygen of the nitre, and its quantity may 

 be determined by dissolving the saline residue 

 in water, supersaturating with nitric acid, and 

 precipitating by a salt of baryta as usual : the 

 process is one requiring more than ordinary 

 care to ensure accuracy. 



To resume the usual process of analysis, we 

 now proceed to determine the bases. Most 

 of the acids may be determined with consi- 

 derable exactness before the organic matter has 

 been destroyed by ignition; it is not so with 

 the bases. Incineration should always precede 

 an attempt to estimate them. The second por- 

 tion of saline matter is dissolved in water a,- 



3 F 2 



