NITRILOSULPHATES. 7 



("52.2 grams carbonate crystals). Sulphur dioxide is passed rapidly 

 into the solution in a flask continuously shaken. When, after a 

 time, the solution grows hot the flask is immersed in cold water, 

 and when it thickens, through temporary separation of acid car- 

 bonate, vigorous shaking of the flask is to be maintained without 

 intermission. As the quantity of the acid carbonate suspended 

 in the warm solution (50°-C>0°) lessens, the rate of current of the 

 sulphur dioxide should be reduced and the action of the solution 

 upon litmus paper closely watched. At the moment the solution 

 reddens the litmus, the entrance of more sulphur dioxide must be 

 stopped, for should acidity to lacmoid paper also be reached through 

 the addition of much more sulphur dioxide, the nitrilosulphate 

 will at once hydrolyse into imidosulphate. During the final slow 

 sulphonation, the solution will generally grow cold enough to begin 

 to deposit small crystals of the nitrilosulphate, recognisable by their 

 brilliant lustre ; these will increase largely in quantity at the 

 temperature of the air. Without waiting too long, it is safer to 

 add two or three drops of concentrated solution of sodium hydrox- 

 ide, sufficient to render the solution faintly alkaline to litmus. 

 It is possible to get more of the salt by evaporating the mother- 

 liquor over sulphuric acid. 



That the reaction proceeds sharply in accordance with the 

 following equation is known from the quantity of imidosulphate 

 which such a solution can be made to furnish : — 



2NaN0 2 + 3Na 2 C0 3 + 8S0 2 =2N(S0 3 Na) 3 +Na 2 S 2 5 + 3C0 2 . 

 In consequence, however, of the great solubility of the nitrilosul- 

 phate the crystals obtained amount to barely more than one-fifth 

 of the total quantity ; still, even that is 120 per cent, of the 

 weight of nitrite taken. The crystals hold 21.8 per cent, of 

 water, or 5011,. Of this quantity it has twice been possible to 



