484: POWDEKS WITH A NITEATE BASE. 



Hence we see how the more or less homogeneous character 

 of the initial mixture, the greater or less duration of combustion, 

 and the varying rapidity of cooling may cause the nature of the 

 final products to vary within very wide limits. There will be 

 occasion to return to these problems, which have a great im- 

 portance in practice. 



20. Hitherto we have examined the final products of reactions 

 taking place at a red heat. In these reactions neither sulphite 

 nor hyposulphite is found, because both these classes of salts 

 are decomposed below this temperature. 



3. DECOMPOSITION OF THE ALKALINE SULPHITES BY HEAT. 



1. We shall distinguish between the neutral sulphites and 

 the metasulphites formerly called anhydrous bisulphites. 



The neutral potassium sulphite may be decomposed into 

 sulphate and sulphide, according to theory 

 4S0 3 K 2 = 3S0 4 K 2 + K 2 S. 



2. A special study was made of this decomposition, which 

 forms one of the most striking distinctions between normal 

 sulphites and metasulphites. 



It was found that the accurate analysis of the products 

 verifies the above equation in the most precise manner, when 

 dry sulphite is brought to a dull red heat in an atmosphere of 

 nitrogen. 1 Several estimations by iodine, made with the 

 requisite precautions, absorbed, for instance, 31'5 c.c., 32'5 c.c., 

 30*8 c.c. of the iodine solution ; while the original salt took up 

 126 c.c. The quarter of the latter figure is just 31/5. 



No sulphurous acid is liberated, contrary to an assertion 

 made by Muspratt, which would require an inexplicable setting 

 free of potash. 



The decomposition of the sulphite does not commence at 

 450, the salt remaining intact till towards a dull red heat, and 

 even at that temperature needing a certain time to be completely 

 transformed. 



3. It is well known that two series of sulphites are dis- 

 tinguished: the neutral, and the acid sulphites, supposed to 

 correspond to the composition of a dibasic acid ; viz. S0 2 K 2 O, 

 and S0 2 KHO, salts which have been studied by Muspratt, 

 Rammelsberg, and De Marignac. 



These investigators have further discovered an anhydrous 

 bisulphite: (S0 2 ) 2 K 2 0. 



In following up his researches on the products of the explo- 

 sion of powder, the author has been led to measure the heat of 



1 Only the sulphite contains, as is always the case, some small amount of 

 a red poly sulphide, a compound which is met with under all the conditions 

 in which the monosulphide alone should be formed. 



