Properties of Pure Substances : Nitrogen, 17 



sufficient here to say that the sulphur was originally precipi- 

 tated from calcium polysulphides by hydrochloric acid ; it 

 was laboriously ground and washed, and distilled five times, 

 and care was taken not to let it take fire. The degree of 

 purity attained was tested by burning off large quantities in 

 a burnished platinum dish, and continuing the process till the 

 residue had disappeared. This product was rather precious, 

 consequently it was made the most of in the present case by 

 using it to coat glass beads : some in powder was also employed 

 near the entrance of the purifying tubes. 



Copper and Silver. — Both bought as pure and deprived of 

 grease by dipping in appropriate acid solutions. 



General Remarks. — -During the two years the apparatus 

 has been in use various accidents, such as the breaking of 

 pumps &c, have at different times caused some of the re- 

 agents to get mixed up, and the apparatus has been taken 

 down and set up again some three or four times ; the first 

 bottles of chromous chloride have also required to be refilled. 

 The phosphorus pentoxide has never required to be touched. 

 I wish to draw attention to a remark of Hittorf's as to the 

 importance of using tubing free from air-bubbles. On 

 several occasions I have been much troubled by the minute 

 leaks which such imperfect tubes give rise to at the joints, 

 and I have in my possession at least two tubes leaking from 

 this cause, but so minutely that even when the leak was 

 localized to within six or seven inches it was impossible to 

 say exactly where it was. In work of this kind the cleaning 

 of the tubes is of course of great importance. If the work is 

 to be done rapidly the great secret is to clean the tube with 

 alcohol before the jointing or general glass-blowing opera- 

 tions are carried out on it. The dirty places are almost 

 always near where the blowpipe-flame has been applied, and 

 after trying all and every means of cleaning, I have finally 

 come back to aqua regia caused to boil at the dirty place and 

 left in the tube for at least ten hours. Certainty of cleaning 

 and jointing has led me to employ English flint glass ex- 

 clusively in this work, and I always use the clean flame of an 

 oxygen-gas blowpipe, which saves time so as to far more than 

 repay the cost of the oxygen. All the blowing required in 

 jointing the tubes is done through a compact but efficient 

 establishment of filtering and phosphoric-acid tubes. The 

 glass springs so extensively used throughout allow of con- 

 siderable latitude in the relative movements of parts of the 

 apparatus, and I have had no cases of spontaneous breaking. 

 The whole of the glass work has been done by myself, as 1 

 can get no assistance of a suitable kind in Sydney, 



Phil. Mag. S. 5. Vol. 35. No. 212. Jan. 1893. C 



