818 



ORGANIC ANALYSIS. 



A mixture of two parts of quicklime and 

 one of hydrate of soda is prepared by slaking 

 some well-burned lime with the necessary 

 quantity of a solution of soda; the whole is 

 evaporated to dryness, ignited, the dry mass 

 pulverized as quickly as possible, and then 

 transferred to well-stopped bottles, in order to 

 exclude carbonic acid and moisture. When an 

 analysis is to be made we proceed as usual, 

 making the mixture in a warm mortar, only 

 substituting the alkalized lime for oxide of 

 copper ; the accidental presence of a little 

 moisture, after the weight of material for ana- 

 lysis is accurately known, is of no consequence 

 in this case. 



Having introduced the mixture, it is better 

 loosely to plug the aperture of the retort with a 

 few fibres of asbestus (which has been ignited 

 just before) to prevent any mechanical trans- 

 port of the mixture into the apparatus through 

 which the gases are passed ; on applying heat 

 to the combustion-tube in the ordinary way, 

 and with the usual precautions, the substance 

 is decomposed, and the whole of the nitrogen 

 escapes as ammonia. The drying tube and 

 potash apparatus are dispensed with, and the 



Fig. 431. 



A. a, mouth of the combustion-tube ; b, three- 

 legged brass tube furnished with the stop-cock 

 (c) ; d, d, caoutchouc connectors; e, glass tube, 

 upwards of 30 inches long, recurved at the lower 

 extremity for delivering gas in the mercurial 

 trough. 



B. Bulb-tube for containing hydrochloric acid 

 in the determination of nitrogen by the method of 

 Varrentrapp and Will. 



C. a, mouth of the combustion -tube ; 6, 

 caoutchouc connector ; c, gas delivering tube. 



ammonia is collected by attaching a bulb-tube of 

 the form represented (jig. 431, B), air-tight with 

 a good cork, to the retort-tube, the apparatus 

 having been previously charged with hydro- 

 chloric acid sp. gr. 1.1, as high as the lines in 



the figures indicate. Pure hydrochloric acid 

 is easily procured for this purpose by diluting 

 the ordinary acid of the shops till it has a 

 sp. gr. of 1.1, and distilling in glass ves- 

 sels the first eighth may be rejected. Dis- 

 tillation may be proceeded with until three- 

 quarters of the acid employed have passed 

 over. It is better for the operator always to 

 rectify his own acid, in order to be quite 

 sure of the absence of any trace of am- 

 monia. The tube connecting the bulbs should 

 be somewhat larger in diameter than that of the 

 ordinary potash apparatus, in order to allow 

 the liquid to be poured out readily. When 

 the operation is complete, absorption will take 

 place and the fluid rise in the bulb nearest the 

 fire; at this moment we nip off the top of the 

 combustion-tube and draw air carefully through 

 the apparatus in the usual way. When the 

 combustion is terminated, the contents of the 

 bulb-tube are emptied into a small evaporating 

 dish, and the apparatus washed out first with a 

 little alcohol and ether, and afterwards several 

 times with water; some solution of bichloride 

 of platinum is added, and the whole evaporated 

 to dryness by a water-bath or chloride of cal- 

 cium bath; when dry, it is digested with a 

 mixture of two parts of alcohol, sp. gr. 833, 

 and one of ether, which dissolves the excess of 

 bichloride of platinum, and leaves the double 

 chloride of platinum and ammonium in a crys- 

 talline form. 



This must now be brought upon a weighed 

 filter, (or better, upon two filters, one of which 

 has been counterpoised against the other,) and 

 washed repeatedly with the mixture of two 

 parts of alcohol and one of ether until nothing 

 further is taken up; the precipitate and filters 

 must be dried by a water heat and the weight 

 accurately observed. According to Varrentrapp 

 and Will, 220.52 grs. of the ammonia-chloride 

 are equivalent to 14 grs. of nitrogen ; the esti- 

 mate of these writers is too high, and 225 grs. are 

 more nearly equal to one equivalent or 14 grs. 

 of nitrogen. Practically, however, their calcu- 

 lation is very near the truth, as during the 

 operation a minute quantity of hydrochlorate 

 of ammonia escapes uncondensed, and the two 

 errors compensate each other. 



This method of determining nitrogen an- 

 swers for all cases excepting those in which it 

 occurs in the form of nitric acid, when it must 

 be determined by volume and its weight thence 

 deduced. For this purpose the process of 

 Dumas is the most trustworthy. A retort tube 

 of about twenty inches long is employed ; not 

 drawn out into a tail, but sealed with a rounded 

 extremity ; about two inches of the tube are 

 filled with carbonate of copper or of lead, and 

 then the mixture with oxide of copper added 

 and covered as usual with a layer of pure 

 oxide ; beyond this the last two or three inches 

 of the tube are filled with clean copper turn- 

 ings, as already directed, to decompose any of 

 the oxides of nitrogen which may be formed. 

 The retort tube is then connected with a three- 

 legged apparatus of brass or copper (fig. 431 , A, 

 b\ one limb of which is furnished with a stop- 

 cock (r). The connection with the retort is 



