HYDBOXYAMIDOSULPHATES BY COrPER SULPHATE. 505 



connected with a tube receiver holding bromine water kept 

 cold, was heated, sometimes quickly, sometimes slowly, either by 

 a spirit lamp or in a bath of sulphuric acid, the solution being 

 finally boiled for some minutes, so as to drive all sulphur dioxide 

 into the bromine water. Before heating, air was removed from 

 the apparatus by a current of carbon dioxide. In one experiment 

 the apparatus was made entirely of glass. The oxidised sulphur, 

 dioxide was weighed as barium sulphate. 



The boiled-out copper solution was titrated with X/10 soda 

 (free from sulphate), using lacmoid paper as indicator. The 

 imperfection of this operation was proved beyond doubt on cal- 

 culating out the nature of the changes which had occurred, but 

 it was serviceable and the best available under the circumstances. 



To the boiling hot solution and precipitate of barium sul- 

 phate, barium chloride was added in excess, the total precipitate 

 collected, well washed, and transferred to a pressure tube in 

 which it was heated with hydrochloric acid for three hours at 

 150°. The barium sulphate was again washed on the filter, then 

 ignited and weighed. The second filtrate and washings contained 

 sulphuric acid, the quantity of which was estimated as barium 

 salt. To make this part of the analytical process intelligible, it 

 must be explained that barium amidosulphate, although itself 

 quite soluble in water, is partially precipitated along with barium 

 sulphate, even in presence of hydrochloric acid (this Journ., g, 

 283). At 150°, the precipitated amidosulphate hydrolyses, yielding 

 barium sulphate and ammonium sulphate in molecular proportions. 



The copper filtrate from the crude barium precipitate was 

 evaporated to a small volume, heated with hydrochloric acid for 

 some hours at 150°, and mixed with barium chloride. The 

 precipitated barium sulphate represented the principal quantity 



