OXlMIDOÖULi'UUXATEc; OK .SULi'HAZuTA'J'ES. 95 



peamncc (if the precipitated siilpliite. lîy efïeeliui^- iieutralisation very 

 slowly at the last until acidity to lacinoïd paper i« jii.st readied, the 

 finish i){ the process may be so hit nÛ' that tlie s(jlution is left free not 

 only from nitrite bnt also from more tlian traces of sulphite. In 

 practice we tind it better to enter the i^'as quickly up to distinct acidity 

 and then at once to stop its flow, for although the solution is then 

 found in contain a not inconsiderable (luantitv of sulphite and to o-ive 

 off a small quantity of nitrous fumes, this hardly affects the vield of 

 oximide, and there is great saving of time and attenticjn. When the 

 method of slow finishing has been followed it is usuallv necessary to 

 add a drop of dilute sulphuric acid at last, to destroy nitrile. 



In the solution, either way prepared, the nitrile present now 

 suffers hydrolysis into imidosulphonate and acid sulphate. To make 

 sure of the disappearance of every trace of this very unstable and 

 therefore injurious salt, the solution is well cooled after the rapidly 

 occurring hydrolysis, and left in its' acid condition for ten or fifteen 

 minutes, while in the case of its containing sulphur dioxide a free 

 stream of air is blown through it to carry this awa3\ For fifteen 

 minutes or so in such a solution, the oximidosulphonate proves able 

 to resist the hych-olysing action of a little sulphuric acid. To the 

 solution deprived of ail nitrile and almost all sulphur dioxide, con- 

 centrated solution of sodium carbonate is added until alkalinity is 

 reached. For this ])urpose about 10 grams of the cai-bonate will be 

 wanted Ijut moiv. sliould be at hand to at once arrest liydrolvsis sliould 

 it happen to have set up in the oximide. 



The liquor is now a solution (jf about ioO grams oximidosul- 

 phonate in about 220 grams of water, along with 15 grams of diso 

 dium imidosulphonate, and 22 of hydrated sodium sulphate. After 

 filtration from any impurities derived from the nitrite it has to be 

 evaporated and this cannot be safelv effected at a steam-lieat. It has 



