228 



EDWARD DIVERS AND TAMEMASA HAGA 



due to the interaction of the acid sulphate and sodium metasulphite, 



the latter salt having- had to be produced in order to secure the sharp 

 sulphonation of the nitrite (This Journal, 6, 66). Much of the loss 

 of the sulphur dioxide, and of the inconvenience caused by its escape, 

 can be easily avoided by distributing, at first, the nitrite solution in 

 several flasks for separate sulphonation, and then allowing the sulphur 

 dioxide regenerated by the hydrolysis of one portion to help in sul- 

 phonating another ; in doing so, the sulphur dioxide may be driven 

 out by heating the hydrolysed solution, without detriment to it, if 

 the heating is not too prolonged. 



In any case, either a short heating is requisite, in order to hasten 

 the second stage in the hydrolysis, (that of imidosulphonate into 

 amidosulphonate and acid sulphate), or else a setting aside of the 

 solution for a few hours (after expelling its sulphur dioxide by 

 a current of air), in order to allow this hydrolysis to complete itself. 

 The solution is next neutralised by adding one mol. sodium carbonate, 

 that is, a third as much as the quantity taken at first, and the solution 

 evaporated, by boiling or otherwise, until it again weighs only 18 

 times as much as the nitrite taken. Exposure of it then in an open 

 vessel for a night, where it may fall to 0° or below, will make nearly 

 all the sulphate present in it separate in large crystals, from which the 

 mother-liquor can be well drained. With less evaporation or less cool- 

 ing, further evaporation of the mother-liquor is needed to separate more 

 sulphate, which seldom crystallises in so good form for draining. It is 

 worth while to dissolve again the sodium sulphate in a third of its 

 weight of water by heat and recrystallise it, to evaporate its mother-liquor 

 to one-fifth and separate sulphate from it by cold, and then add it to 

 the main quantity of mother-liquor. 



The solution of sodium amidosulphonate, filtered from some 

 turbidity usually present in it, is now mixed with concentrated sul- 



