AMIDOSULPHOXIC ACID. 249 



phonic acid which has been extracted from the original precipitate 

 (along with some barium) is then to be estimated by concentrating the 

 second filtrate and washings and heating at 150° in sealed tube, to 

 convert the amidosul phonic acid into sulphuric acid, which is, lastly, 

 weighed as barium salt. This represents half the sulphur present in 

 the original precipitate as imidosulphonate ; when, therefore, its weight 

 is deducted from that of the sulphate got from that precipitate by the 

 treatment with hydrochloric acid, the difference is the sulphate present 

 in the vitreous mass. We made use of this method, with sufficient 

 success, in the earlier work done upon it. 



The extent to which the acid is decomposed by heating it to 

 about 220° or to 26*5°, for twenty to thirty minutes, hardly varies from 

 93 per cent, (corrected, probably «)0 per cent.), as the following com- 

 parison shows. 



Calc. 220° 265° 265° 



Sulphate sulphui 



"".01 23.04 23.02 



a.)l 23 - ( 



(inch that by hyd.) 



Sulphate sulphur ^ 



, \ l5 ' U 15 ' 53 



(by heat alone) j 



Ammonia nitrogen, 10.0G 10.00 10.15 



Residual acidity, 76.75 70.73 77.00 



But as the acid used had always with it at least one per cent, water, 

 partly as moisture, partly combined as ammonium hydrogen sulphate, 

 it is probable that the decomposition of the thoroughly dry acid would 

 extend to less than 90 per cent, of it. This is, however, hardly, a 

 point of consequence. 



On heating the acid much above 2(50°, the products first formed 

 enter into decomposition. A portion of six or eight grams melted and 

 further heated, over a small flame, in an open platinum crucible, forms 

 Inrge tenacious bubbles, until somewhat more than a tenth has boiled 



