190 Dr. Herapath on the Chemical Constitution of the 



iron filings ; these were then heated red-hot, the organic mat- 

 ters were decomposed and reduced to pure carbon, and the oxide 

 of iron was reduced to the metaUic state ; when the gas issuing 

 from the exit-tube of the apparatus burnt with a steady, yellow 

 flame, the operation was discontinued; at least the spirit-lamp 

 was removed and the iron allowed to cool, still in an atmo- 

 sphere of dry hydrogen gas, and when cold, removed and well 

 secured in a small stoppered bottle. 



To the same apparatus for generating the dry hydrogen was 

 adapted a counterpoised test-tube (a), and to the exit-pipe from 

 this was connected a tube containing chloride of calcium, this 

 tube, with its contents, being accurately counterpoised. Into 

 the counterpoised test-tube («) was placed a mixture of 10'3 

 grs. of the crystals previously dried at 212°, rubbed up in a 

 mortar with 50 grs. of the purified iron filings ; the mortar was 

 vriped out carefully by 20 grs. of the same iron, and this also 

 inserted in the tube, a layer of pure iron filings placed over the 

 whole, and the tube, with its fittings, again weighed. 



This part of the apparatus was then placed in a flask contain- 

 ing a solution of chloride of zinc — destined to act as a bath : 

 the whole apparatus having been satisfactorily adjusted, heat was 

 applied to the bath, and gradually raised until the chloride of 

 zinc ceased to give ofi" any water, and of course fused ; this must 

 have been 420° Fahr. or more. 



In this operation the crystals were decomposed ; the iron seized 

 the iodine as fast as it was liberated ; the quinine retained the 

 sulphuric acid ; and the current of dry hydrogen gas carried over 

 the aqueous vapour to the chloride of calcium tube, where it was 

 retained: the increase in weight was 1'44 r^rs. : then as 10"2 

 : 1-44 : : 100 : 14-1764 of water. 



This method was also adopted as a means of estimating the 

 iodine, but for this purpose the chloride of zinc bath was not em- 

 ployed, as a more perfect decomposition was then necessaiy ; the 

 mass in the test-tube {a) was lixiviated repeatedly, as long as any 

 iodide of iron was dissolved; this was at once filtered into a solu- 

 tion of nitrate of silver, iron filings being kept in the filter to avoid 

 decomposition ; the filter was repeatedly washed with boiling di- 

 stilled water, and of course the washings added to the previous 

 liquid ; the resulting mixture of iodide of silver with the oxides 

 of iron was thrown on a filter, washed with hot diluted hydro- 

 chloric acid as long as any iron was removed, then with ammo- 

 nia to i-emove any chloride;, and then with distilled water ; dried 

 and ignited, it weighed 0"00 grs. = iodine 3'1453=per cent. 

 31*453, corresponding very closely with that previously ob- 

 tained. A second analysis, specially directed to the estimation 

 of the-sulphuric acid, gave 10"844 per cent, as the result. 



