LABORATORY NOTES. 



331 



repeated. A few drops of tartaric acid solution are added and 

 20c. c. of hot water, the solution filtered into a oODc.c. beaker, 

 the insoluble residue washed free from hydrochloric acid with hot 

 water. In order to reduce mo>t of the ferric chloride, and so pre- 

 vent the precipitation of large quantities of sulphur by sulphuretted 

 hydrogen, the solution is warmed with 2c. c. of saturated solution 

 of ammonium bisulphite tdl smell of sulphur dioxide has dis- 

 appeared and diluted to about 250c. c. ; sulphuretted hydrogen is 

 then passed through the heated solution till the precipitate becomes 

 dense and granular and the excess of sulphvu'etted hydrogen driven 

 off in the ordinary manner by a current of washed carbon dioxide. 

 The precipitate is then hltered on a weighed Gooch filter, washed 

 with hot water containing a little sulphuretted hydrogen and 

 drained with the filter pump. The cap is placed on the bottom of 

 the crucible, which is then transferred to the special air bath 

 designed by Paul and figured in his paper. It consists of an iron 

 bath, inside which the Gooch crucible is supported in the enlarged 

 upturned end of a glass tube, tlirough which the current of carbon 

 dioxide is passed. This enlarged end of the glass tube is covered 

 with a small watch glass and the whole bath closed by^ a clock 

 The apparatus we use is of the following dimensions : — 



The current of carbon dioxide is then turned on and heat applied 

 by means of a couple of large Bunsens or a Fletcher's burner; a 

 slow current of carbon dioxide is kept going continuously, the 

 temperature kept between 220° ami 230° C. for half an hour. The 



