4 P. T. Cleve, 



the oxygen by dissolving the peroxide in a mixture of sulphuric acid 

 and ferrous-ammonia sulphate and titrating the unoxidised ferrous salt. 

 Three different experiments gave for 100 DigOg only 0.74, 0.86 and 0.90 

 parts oxygen. This method is, I believe, very exact. I have used it to 

 determine the oxygen in peroxide of h3^drogen, and 1 obtained exactly 

 the same result as that arrived at by determining the peroxyde of hy- 

 drogen with permanganate of potash, which is a very exact method. 



I conclude from my experiments that the loss by ignition of the 

 peroxide is either occluded oxygen or is occasioned by the presence of 

 small quantities of basic nitrate, which have escaped decomposition. It 

 is not possible to calculate a probable formula for the peroxide, prepa- 

 red on the dry way. 



I then tried to obtain the peroxyde by mean of peroxyde of hy- 

 drogen. The latter was obtained from Mr. Trommsdorff in Erfurt and 

 was of great purity. 



The cold solution of the nitrate of didymium was mixed with a 

 much more than sufficient quantity of the peroxyde of hydrogen and a 

 solution of pure caustic potash added. A gelatinous precipitate, in all 

 respects resembling the hydroxyde of didymium, was thrown down; 

 after a short time an abundant disengagement of oxygen commenced. 

 The precipitate was rapidly and completely washed in darkness and at 

 ordinary temperature and immediately subjected to analysis. The ma- 

 terial used for the experiments 1 — 4 was obtained in the above manner. 

 For the experiments 5 — 6 the peroxyde was prepared from sulphate of 

 didymium. The oxygen was determined by mixing the peroxyde with a 

 known weight of ammonium ferrous sulphate and free sulphuric acid, 

 the unoxidised ferrous sulphate being then determined by titration with 

 permanganate. The didymium was afterwards precipitated with oxalic 

 acid and the oxalate ignited. The following results were obtained: 



Peroxyde-oxygen Oxygen on 100 parts DjOj 



0.0.519 gram 8.08 



0.0390 » 8.10 



0.0407 » 8.17 



0.0381 » 7.98 



0.0504 >:> 8.13 



0.0476 » 8.27 



