Effect of Temperature, Acidity, etc. 395 



was first constricted at a point about 50 cm from the closed end, 

 to a diameter of 6 or 8 millimeters. The ferrous sulphate and 

 sulphur were then dropped in through a long funnel ; a suf- 

 ficient quantity of a titrated sulphuric acid (30 per cent con.) 

 was measured out from a burette into a graduated cylinder, 

 enough water added to make 75 cc and the resulting solution 

 poured into the tube. The tube was then packed in ice, 

 saturated with hydrogen sulphide and quickly sealed at the 

 constriction, after which it was placed in a steel bomb sur- 

 rounded by water and closed up. The bomb was finally put 

 into a suitable furnace already heated to a degree such as to 

 bring the bomb to the desired maximum temperature. For 

 details of bomb and furnace construction a former paper* 

 should be consulted. At the end of a period of from 1-4 days, 

 depending on the temperature of the experiment, the bomb 

 was withdrawn from the furnace, cooled and opened, and the 

 tube then removed. The glass tube should never be so long 

 that it cannot be entirely covered by water ; partially covered 

 tubes are very apt to break. 



B. Purification of the synthetic products. — The glass tube 

 is opened and the contents quantitatively transferred to a suit- 

 able beaker. The sulphide is then filtered out while the 

 filtrate is caught in a measuring flask of 250 cc capacity and, 

 after adding the washings, diluted up to the mark. 



In the solution the acid is determined by titrating with a 

 standard sodium carbonate solution using methyl orange as 

 indicator. The excess of hydrogen sulphide, or of sulphur 

 dioxide, which forms when the temperature and acidity are 

 sufficiently high, should first be removed by boiling in a cur- 

 rent of carbon dioxide. The sulphide needs to be carefully 

 freed from sulphur in all cases, and it was thought best to get 

 rid of the siliceous matter originating from the glass when the 

 products were formed at the highest temperatures. To this 

 end the wet sulphide is first dried by washing with alcohol and 

 ether and sucking off with the pump. Most of the sulphur is 

 then dissolved out by carbon bisulphide, - but the film which 

 commonly persists and coats the sulphide as the last portions of 

 the volatile solvent evaporate, should be removed by concen- 

 trated colorless ammonium sulphide, after the excess of carbon 

 disulphide has been washed out by ether. The excess of 

 ammonium sulphide is then removed by water and the product 

 finally dried with alcohol and ether ; or if siliceous material is 

 present the product should be warmed with a mixture of 

 hydrofluoric and hydrochloric acids for half an hour on the 

 steam-bath. The sulphides should be kept in a vacuum desic- 

 cator. When they are to be tested by the Stokes reaction 



*Loc. cit. 



