OXTMIDOSULPHONATES OR SULPHAZ( JTATES. 45 



perature has risen In l.Si^-3° when it sudden! v decomposes into a loose 

 unfiised residue, vapours depositing- a very small sublimate, and gases. 

 The residue is neutral or slightly alkaline and consists of sodium 

 sulphate witli a very little thiosulphate. The very small sublimate 

 consists ofsulphiu- and ammoniacal salt which when acidified yields a 

 solution milky from sulphur and smelling fain tlv of sulphur dioxide. 

 The gases are sulphur dioxide and nitrogen in nearly eipial volumes. 



Neglecting the very small <|uantities of sulphur, thiosulphatt;. 

 and ammonia, all due to water retained by the salt, the decomposition 

 may be written : — 



2Xa,NS,0, = 3Na,S0,+ SO.+K,. 



The anhydrous disodium salt liegins to give off gas in a ^'^^cuum, 

 but exceedingly slowly, at about I4<P, and continues to do so nearly 

 as slowly while the temperature is rising to about 170°, or while it is 

 maintained steadily at any intermediate j^oint. When the tem}3erature 

 is allowed to rise continuously though slowly the full decomposition 

 of the salt occurs suddenly at 171°, whilst when it is kept steady for 

 an hour or more at about 165° and then slightly raised, full decom- 

 position occurs suddenly at 1(37-8°. At the moment of active decom- 

 position the salt fuses and effervesce« and, like the trisodium salt, 

 yields a small sublimate as well as gases. The i-esidue is exceedingly 

 acid and consists of sodium acid-sul])hate with a not inconsiderable 

 quantity of ammonium acid-sulphate or more probably the correspond- 

 ing pyrosulphates. The sublimate is a compound of ammonia and 

 sulphur dioxide while the gases consist of nitrogen and sulphur 

 dioxide, the former in somewhat greater volume than the latter. 

 Nitrous oxide could not be detected by us ; liut in one experiment the 

 sulphur dioxide constituted more thiin half the total gas, a result only 

 to be explained as due to some undetected error ov to the presence of 



