AMIDOSULPHOXIC ACID. 229 



phuric acid, 3 — 3.^ times the weight, of nitrite taken, and set aside for 

 a day in a cool place. Most of the amidosul phonic acid separates im- 

 mediately, — what of the rest can he secured, crystallises out during the 

 cooling and standing. It is well drained on porous tiles, and washed 

 with a little ice-cold water. 



The yield of acid by this process is atfected by the tendency of 

 the acid to form crystals with sodium hydrogen sulphate (see the 

 account of the salts), and, therefore, sodium sulphate should be 

 separated as much as possible, before adding the sulphuric acid. 

 But a yield of 75 per cent, of the calculated quantity may be counted 

 on. while much more can be obtained. 



To get the acid pure and in good crystals, it must be recrystallised. 

 This can be done, without considerable waste, by grinding it fine, 

 adding it to 2| times its weight of boiling-hot water, and stirring 

 diligently on a, water bath until it is all dissolved. The solution 

 set aside yields up about three-fifths of it, and the mother- 

 liquor by cold evaporation will yield nearly all the rest in fine 

 crystals, in spite of the hydrolysis which the hot water will have 

 caused. Mother-liquors may also be worked up by precipitating the 

 acid by means of strong sulphuric acid, or by alcohol.* 



Properties of the acid. 



Amidosulphonic acid is- without odour or colour and has a sharp, 

 purely acid taste (Berglund). From its aqueous solution it crystallises 

 readily, and better than most of its salts (Berglund). Its crystals are 

 orthorhombic plates ; Fock (see Raschig's memoir) has examined it 

 crystallographically, and shown it to be isomorphous with its 

 potassium salt. 



* For another, sometimes useful, way of preparing the acid, see p. 236. 



