POTASSIUM HYPOSULPHITE NOT FOKMED. 497 



The variations are wider when we pass to powders in which 

 the proportion of nitre is different, such as sporting and blast- 

 ing powders, but we suppress these data in order not to unduly 

 extend our explanations. 



10. These analyses give rise to various remarks. It should 

 in the first place be noted that the sulphur observed is not free 

 in reality, but combined, partly in the form of potassium poly- 

 sulphide, and partly as iron sulphide (or rather of double 

 sulphide of iron and potassium), resulting from the action on 

 the walls of the vessels. This phenomenon manifested itself to 

 the greatest extent in Noble and Abel's experiments, but it is 

 far less appreciable in firearms owing to the rapidity with 

 which the products are cooled by expansion and expelled. 



11. For a long time potassium hyposulphite, which appears 

 in the analyses of Bunsen, Linck, Federow, and in the early 

 publications of Noble and Abel, as representing an amount 

 sometimes very considerable, had been admitted among the 

 products of the combustion of powder. The author had called 

 attention some years since to the fact that this compound could 

 not be an initial product of the combustion of powder, since it 

 is completely decomposed by heat towards 450 into sulphate 

 and poly sulphide (see p. 487). At the very most the presence 

 of some trace of it might be admitted, due to the secondary 

 reactions taking place during cooling. But the considerable 

 amounts observed by writers on the subject appeared attributable 

 to the alteration of the products produced both by contact with 

 the air and during the analytical manipulations. 



Shortly afterwards Debus confirmed this opinion, and dis- 

 covered that the hyposulphite found was attributable chiefly to 

 the reactions of the potassium polysulphides on the copper oxide 

 employed in the analysis to separate the sulphur from the 

 alkaline sulphide. Thus at the present day hyposulphite has 

 disappeared from the list of the essential products formed 

 during the combustion of powder. 



12. It will further be remarked that in exceptional cases 

 a small quantity of charcoal escapes combustion. A small 

 quantity of nitre up to three thousandth parts is almost always 

 found. 



Lastly, some powders would yield free potash up to three per 

 cent. ; a sign of some dissociation of which the suddenness of 

 cooling or of solidification has preserved a trace; this potash 

 not having had time to unite with the carbonic acid of the 

 superposed atmosphere. 



The free oxygen which would result from some analyses may 

 be attributed either to particles of nitrate remaining isolated in 

 the mass and decomposed by the high temperature of the explo- 

 sion, or more probably to the dissociation of the carbonic acid 

 (see p. 504), and the sudden cooling of the mass, which did not 



2 K 



