324 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Determination of Sulphur in Pyrites. — This import- 

 ant analytical operation has given much trouble to chemists, but 

 there is hardly another process that has received so much study 

 and has produced so much literature as this, so that it would seem 

 that the methods in use must have been perfected in all of their 

 details. Recent investigations by Hintz and Weber show, how- 

 ever, that there is a serious source of error in Lunge's method as 

 applied by many chemists. They find that when barium chloride 

 solution is added slowly to the acidified solution containing 

 ammonium sulphate the amount of barium sulphate obtained is 

 decidedly less than when the reagent is added rapidly. They 

 find that in the first case the barium sulphate contains ammonium 

 sulphate which volatilizes upon ignition and leads to a loss of 

 sulphur. This unexpected result recalls to the reviewer a variety 

 of natural barite from Missouri in which Ludeking and Wheeler 

 (this Journal III, xlii, 495) found 0'2 per cent of ammonium 

 sulphate, a circumstance which shows the tendency of ammonium 

 sulphate to crystallize with barium sulphate. Hintz and Weber 

 give the following directions for determining sulphur in pyrites : 

 Treat 0'5 g of pyrites with 10 co of a mixture of 3 parts of nitric 

 acid, 1*42 sp. gr., and 1 part of hydrochloric acid, 1*17 sp. gr., 

 allow the action to go on in the cold at first, and finally complete 

 the decomposition on a boiling water-bath. Then transfer the 

 liquid to a porcelain dish, evaporate to dryness on the water-bath, 

 moisten with 5 CC of concentrated hydrochloric acid, and evapor- 

 ate again. Take up the residue with l cc of hydrochloric acid, 

 1*17 sp. gr., and about 100 cc of hot water, filter through a small 

 filter and wash the residue at first with cold, finally with hot 

 water. Add to the filtrate, of somewhat more than 150 cc volume, 

 while warm, 20 cc of 10 per cent ammonia and heat about 15 min- 

 utes to about 70°. Filter off the ferric hydroxide precipitate and 

 wash it with hot water until the volume has reached about 450 cc . 

 Add a little methyl orange, neutralize with hydrochloric acid and 

 add l co of hydrochloric acid, 1*17 sp.gr. in excess. Heat until 

 boiling begins and precipitate with a boiling solution of 24 cc of 

 10 per cent barium chloride diluted to 100 ce , adding the reagent 

 at one time as rapidly as possible with vigorous stirring. Rinse 

 the iron precipitate from the filter, dissolve it in as little hydro- 

 chloric acid as possible, precipitate warm with ammonia, filter, 

 and wash the precipitate. Heat the filtrate and washings until 

 the greater part of the ammonia has been driven off, acidify 

 slightly with hydrochloric acid, and treat with some barium chlo- 

 ride solution. If any barium sulphate is found here, add it to the 

 main precipitate. Filter the barium sulphate precipitate, washing 



