1880.] 



Fired Gunpowder. 



201 



was perfectly colourless. In a few instances the oxide was added in 

 small quantities at a time, in others the sufficient excess was added 

 at once, with no difference in the result obtained. The only points 

 in which this method differed from that described by Bunsen and 

 Schischkoff in their memoir, was in the employment of a flask well 

 closed with an india-rubber bung for the stoppered cylinder which 

 was employed by them ; and in occasionally curtailing somewhat the 

 prescribed period (two days) for which the liquid and the copper 

 oxide were allowed to remain together, the operation being considered 

 complete when the solution had become colourless. Bunsen and 

 Schischkoff prescribed that the liquid when separated by filtration 

 from the mixed copper oxide and sulphide obtained in the foregoing 

 treatment, is to be divided into seven equal volumes, in one of which 

 the amount of hyposulphite may be most simply estimated by acidi- 

 fying it with acetic acid, and then titrating with a standard iodine 

 solution. This course was adopted by us, and it will therefore be 

 seen that we departed in no essential point whatever from the method 

 of Bunsen and Schischkoff, which we had considered ourselves fully 

 warranted in adopting, without questioning its trustworthiness. 



We were informed, however, last July by Dr. Debus, that in sub- 

 mitting potassium polysulphides to treatment with copper oxide, he 

 had found much hyposulphite to be produced, even when air was 

 perfectly excluded, it having been in the first instance ascertained 

 that the several polysulphides experimented with did not contain any 

 trace of hyposulphite. We proceeded at once to confirm the correct- 

 ness of his observations, by submitting potassium polysulphides to 

 treatment with copper oxide, proceeding exactly according to the 

 method prescribed by Bunsen and Schischkoff for the treatment of 

 powder residues. In one experiment we obtained as much as 87"1 

 per cent, of potassium hyposulphite (calculated upon 100 parts of 

 potassium monosulphide). Even in an experiment with pure potas- 

 sium monosulphide, we obtained 11*6 per cent, of hyposulphite upon 

 its treatment for the usual period with copper oxide. 



We next proceeded to convince ourselves that by substituting zinc 

 chloride solution for copper oxide, the sulphur existing in solutions 

 of potassium mono- and poly- sulphides might be abstracted, accord- 

 ing to the usual method of operation, without producing more than 

 the very small quantities of hyposulphite ascribable to the access of 

 a little air to the sulphides before or during the method of treatment. 



Having confirmed the validity of Dr. Debus' objection to Bunsen 

 and Schischkoff's method, and established the trustworthiness of a 

 modification of that method (zinc chloride being substituted for copper 

 oxide), we proceeded to submit to precisely similar treatment with 

 these two reagents portions of solutions obtained by dissolving, with 

 total exclusion of air (in the manner described in our last memoir 



